High-precision measurements of the triple oxygen isotope ratios (δ¹⁸O and Δ‘¹⁷O) in terrestrial waters, rocks and minerals opened new and exciting applications in the field of stable oxygen isotope geochemistry. After giving a short overview over measurement techniques and various applications, it will be emphasized on tracing the atmospheric composition in rocks and minerals.

Atmospheric samples from ice cores only date back ~1 Myrs. To obtain information about the atmosphere for the 99.98% of Earth history that is not covered by ice cores, we need to look for rocks. The oxygen isotope composition of the atmosphere younger than 2.4 Gyrs is dominated by molecular oxygen (O₂). Molecular O₂ is one of few components on Earth that has a mass-independent oxygen isotope signature. The anomaly in ¹⁷O provides information about the presence of an ozone layer, the global biosphere primary production, or the atmospheric CO₂ mixing ratio. A few rocks and fossils provide information about the ¹⁷O anomaly of air O₂. Sedimentary sulfates may form by precipitation from SO₄^2- that formed by subaerial oxidation of pyrite. In that process, a part of the oxygen in the sulfate originates from air O₂. Mobilizing of the sulfate oxygen can carry this anomaly over to other minerals like Fe oxides. The isotope signature of fossil tooth enamel also provides information about the atmospheric composition. Air O₂ is inhaled and used to oxidize carbohydrates and fat to (mainly) CO₂ and H₂O, which equilibrate with body water. Tooth apatite then precipitates from body water and inherits an anomaly in ¹⁷O from the inhaled air O₂. Manganese oxides are known to form by oxidation of Mn under participation of O₂. If the isotope composition of dissolved O₂ in the aqueous environment, in which the manganese oxides form is controlled by air, manganese oxides can be used to trace the composition of air O₂. It has been shown that some meteorite impact melts (tektites) have exchanged with ambient air O₂. As result of that exchange, they carry a ¹⁷O anomaly that may be used to trace the composition of air O₂. Also, I-type cosmic spherules have been shown to be indicators for the isotope anomaly of air O₂. These spherules form by aerial oxidation of asteroidal metallic Fe,Ni particles and thus can carry the anomaly of air O₂. Such recent discoveries open insights into the composition of the Earth atmosphere beyond the 1 Myrs limit from the ice core record.

How to cite: Pack, A., Fischer, M., Stübler, C., Peters, S., and Feng, D.: Tracing the triple isotope composition of air by high-precision analyses of meteorites, rocks and fossils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18899, https://doi.org/10.5194/egusphere-egu2020-18899, 2020.

Oxygen isotopes are a widely used tracer in the field of paleoceanography and provide unique information on mineral formation and environmental conditions. Carbonate sediments record a shift in δ¹⁸O of 10 to 15‰ from the Archean towards higher values in the Phanerozoic. Three different scenarios are suggested to explain this observation: (I) hot Archean oceans, (II) depletion of ¹⁸O in Archean oceans compared to present day and (III) diagenetic alteration of the primary isotopic signature [1]. Recent advances in high-resolution gas source isotope ratio mass spectrometry provide a new tool that may allow to decipher the origin of this isotopic shift observed in the early rock record. We performed high-precision ¹⁸O/¹⁶O and ¹⁷O/¹⁶O measurements on oxygen ion fragments (¹⁶O⁺, ¹⁷O⁺, ¹⁸O⁺) generated in the ion source from CO₂ gas [2]. Isobaric interferences on m/z=17 (¹⁶OH⁺) and m/z=18 (H₂¹⁶O⁺) are separated by means of high mass resolution. The CO₂ gas is first liberated from carbonate samples by orthophosphoric acid digestion and then analyzed on a Thermo Scientific Ultra dual-inlet gas source isotope ratio mass spectrometer [3]. By adding the dimension of ¹⁷O/¹⁶O to the classical ¹⁸O/¹⁶O system, equilibrium trajectories of carbonates that are defined by the equilibrium fractionation factor (¹⁸a_eq) and the triple isotope fractionation exponent (θ) can be predicted as a function of temperature. Minerals that were altered by or formed in meteoric water can be distinguished from those that precipitated in equilibrium with ambient sea water. Therefore, triple oxygen isotope analysis of carbonates does not only hold the potential for a new single-phase paleothermometer, but may also be used to trace the origin of carbonates. Here, we present high-precision triple oxygen isotope data for carbonates from the Pilbara and the Kaapvaal cratons that cover nearly one billion years from the Paleoarchean to the Paleoproterozoic. Marine carbonates from the Phanerozoic complement the dataset. The carbonates were formed in different marine settings, from shallow marine stromatolites to carbonates grown in the interstitial space of basaltic pillows. Phanerozoic carbonates record equilibrium conditions with modern sea water at moderate temperatures. The majority of Precambrian carbonates plot below the predicted equilibrium curve in the δ’¹⁸O-Δ‘¹⁷O space and do not reflect equilibrium conditions with modern sea water at elevated temperatures that were proposed for the Archean oceans. Modeling the triple oxygen isotope composition of carbonates in equilibrium with sea water, that is depleted in ¹⁸O also cannot explain the observed isotopic shift. Further modeling of post-depositional alteration suggests that most carbonates interacted and re-equilibrated with meteoric waters at variable water-rock ratios and temperatures.

[1] Shields and Veizer, 2002, Geochem., Geophy., Geosyst., 10.1029/2001GC000266
[2] Getachew et al., 2019, Rapid Commun. Mass. Spectrom., 10.1002/rcm.847
[3] Eiler et al., 2013, Int. J. Mass. Spectrom., 335, 45-56.

How to cite: Jäger, O., Surma, J., Albrecht, N., Marien, C. S., Xiang, W., Schier, K., Bau, M., Reitner, J., and Pack, A.: High-precision triple oxygen isotope analysis of Archean and Proterozoic carbonates , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17881, https://doi.org/10.5194/egusphere-egu2020-17881, 2020.

Hydrothermal circulation of seawater at mid-ocean ridges cools the oceanic crust and modulates the oceanic chemistry over multimillion-year time scales. Recent research on mass-dependent fractionation of triple oxygen isotopes allows us to gain a new insight into the seawater-basalt exchange reactions that occur within the oceanic crust. To understand the systematics of triple oxygen isotope exchange, we present a novel combined dataset for Δ¹⁷O and ⁸⁷Sr/⁸⁶Sr isotope values measured in modern seawater-derived vent fluids at the Axial Seamount volcano located on the Juan de Fuca Ridge and oceanic epidotes extracted from altered mid-ocean ridge basalts. Upon reaction with fresh oceanic crust, seawater evolves towards the low Mg compositions characteristic of fluids in equilibrium with basalt. In concert with decreasing Mg content and with decreasing ⁸⁷Sr/⁸⁶Sr, the vent fluids at Axial Seamount shift towards values that are 0.04 ‰ lower in Δ¹⁷O and 2 ‰ higher in δ¹⁸O compared to initial seawater. The ⁸⁷Sr/⁸⁶Sr and Δ¹⁷O values of epidotes extracted from modern hydrothermally altered basalts reveal a trend of isotope exchange similar to the one defined by the fluids. We suggest that epidotes record isotope shifts that were experienced by fluids in the areas of focused flow within the oceanic crust. Both fluids and epidotes display similar trajectories of Δ¹⁷O and ⁸⁷Sr/⁸⁶Sr shifts which are modeled using a Monte-Carlo simulation of reactive transport in dual-porosity medium. These trajectories provide important constraints on the physical complexity of reactive circulation of seawater within the oceanic crust. We show how the contribution of hydrothermal circulation to the isotope budget of seawater can be changed during geologic history and evaluated based on the studies of fragments of ancient oceanic crust.

How to cite: Zakharov, D., Tanaka, R., Lundstrom, C., Butterfield, D., Reed, M., and Bindeman, I.: Hydrothermal seawater-basalt exchange reactions traced by triple oxygen and strontium isotope values of fluids and epidotes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21469, https://doi.org/10.5194/egusphere-egu2020-21469, 2020.

Water isotopic composition is a key proxy for past climate reconstructions using deep ice cores from Antarctica. As precipitation forms, the local temperature is imprinted in the snowfalls δ¹⁸O. However, this climatic signal can be erased after snow deposition when snow is exposed to the atmosphere for a long time in regions with extremely low accumulation. Understanding this effect is crucial for the interpretation of ice core records from the extremely dry East Antarctic Plateau, where post-deposition processes such as blowing snow or metamorphism affect the physical and chemical properties of snow during the long periods of snow exposure to the atmosphere. Despite the importance of these processes for the reliable reconstruction of temperature from water isotopic composition in ice cores, the tools required to quantify their impacts are still missing. Here, we present a first year-long comparison between (a) time series of surface snow isotopic composition including d-excess and ¹⁷O-excess at Dome C and (b) satellite observations providing information on snow grain size, a marker of surface metamorphism. Long summer periods without precipitation tend to produce a surface snow metamorphism signature erasing the climatic signal in the surface snow δ¹⁸O. Using a simple model, we demonstrate that d-excess and ¹⁷O-excess allow the identification of the latent fluxes induced by metamorphism, and their impact on surface snow isotopic composition. In turn, their measurements can help improve climate reconstructions based on δ¹⁸O records ice by removing the influence of snow metamorphism.

How to cite: Casado, M., Landais, A., Picard, G., Arnaud, L., Dreossi, G., Stenni, B., and Prie, F.: Using triple water isotopes signatures of surface snow to gauge metamorphism in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-44, https://doi.org/10.5194/egusphere-egu2020-44, 2020.

The oxygen isotope signature of leaf water is used to trace several processes at the soil-plant-atmosphere interface. During photosynthesis, it is transferred to the oxygen isotope signature of atmospheric CO₂ and O₂, which can be used for reconstructing past changes in gross primary production. The oxygen isotope signature of leaf water additionally imprints leaf organic and mineral compounds, such as phytoliths, used as paleoclimate and paleovegetation proxies when extracted from sedimentary materials.

Numerous experimental and modelling studies were dedicated to constrain the main parameters responsible for changes in the δ¹⁸O of leaf water. Although these models usually correctly depict the main trends of ¹⁸O-enrichment of the leaf water when relative humidity decreases, the calculated absolute values often depart from the observed ones by several ‰. Moreover, the δ¹⁸O of leaf water absorbed by plants is dependent on the δ¹⁸O value of meteoric and soil waters that can vary by several ‰ at different space and time scales. These added uncertainties make our knowledge of the parameters responsible for changes in the δ¹⁸O of leaf water and phytoliths flawed.

Changes in the triple oxygen isotope composition of leaf water, expressed by the ¹⁷O-excess, are controlled by fewer variables than changes in δ¹⁸O. In meteoric water the ¹⁷O-excess varies slightly as it is weakly affected by temperature or phase changes during air mass transport. This makes the soil water fed by meteoric water and the atmospheric vapour in equilibrium with meteoric water changing little from a place to another. Hence the ¹⁷O-excess of leaf water is essentially controlled by the evaporative fractionation. The latest depends on the ratio of vapor pressure in the air to vapor pressure in the stomata intercellular space, close to relative humidity. Leaf water evaporative fractionation can lead to ¹⁷O-excess negative values that can exceed most of surficial water ones.

Here we present the outcomes of several recent growth chamber and field studies, for the purpose of i) refining the grass leaf water and phytoliths δ¹⁸O and ¹⁷O-excess modelling, ii) assessing whether the δ¹⁸O and ¹⁷O-excess of grass leaf water can be reconstructed from phytoliths, and iii) examining the precision of the ¹⁷O-excess of phytoliths as a new proxy for past changes in continental atmospheric relative humidity. Atmospheric continental relative humidity is an important climate parameter poorly constrained in global climate models. A model-data comparison approach, applicable beyond the instrumental period, is essential to progress on this issue. However, there is currently a lack of proxies allowing quantitative reconstruction of past continental relative humidity. The ¹⁷O-excess signature of phytoliths could fill this gap.

How to cite: Alexandre, A., Outrequin, C., Vallet-Coulomb, C., Landais, A., Piel, C., Devidal, S., Peugeot, C., Ouani, T., Afouda, S., Couapel, M., Sonzogni, C., Mazur, J.-C., Prié, F., and Webb, E.: Factors controlling the triple oxygen isotope composition of grass leaf water and phytoliths: insights for paleo-environmental reconstructions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6641, https://doi.org/10.5194/egusphere-egu2020-6641, 2020.

The carbonate ¹⁷O anomaly (Δ¹⁷O) has recently been developed as a geochemical proxy for estimating the relative humidity of moisture at the source point of evaporation, which can be a vital tool in paleoclimate research. Speleothem Δ¹⁷O variability in particular may provide a quantitative constraint on moisture regimes at millennial and orbital timescales—far longer than can be addressed by analyzing ¹⁷O in other materials, such as tree rings. Modern observations and calibration studies have established a robust negative correlation between the Δ¹⁷O (¹⁷O excess) of rainfall and relative humidity, so that Δ¹⁷O is enhanced during arid conditions at the moisture source. Herein, we report novel triple oxygen isotope data across the Last Glacial in speleothems collected from Cherrapunji Cave, northeastern India. Triple oxygen isotope measurements were obtained by an O₂-CO₂ Pt-catalyzed oxygen-isotope equilibration method. Preliminary results suggest lower Δ¹⁷O in speleothems during cold periods (e.g. Heinrich Events), which would imply higher relative humidity over the oceanic moisture source. Importantly, higher source relative humidity does not necessarily imply changes in precipitation amount at the cave site. While it is possible that a substantial geographic shift in the moisture source region (or additional contributions from secondary sources) could obfuscate the Δ¹⁷O signal, we argue that this explanation is unlikely for our study site. Alternatively, we cannot exclude the effects of excessive moisture recycling in the tropical ocean, which can enhance the ¹⁷O anomaly in cloud vapor (particularly if combined with large temperature swings) and thereby alter speleothem Δ¹⁷O. To refine our interpretation of the Δ¹⁷O signal in Cerrapunji Cave samples, we investigate multiple cold periods, as well as coeval samples from the Asian Summer Monsoon region. Finally, we compare our results with novel data from westernmost Asia, where temperature variations during cold events are more likely to be accompanied by large shifts in predominant moisture source, due to the migration of wintertime westerlies.

How to cite: Mahata, S., Duan, P., Sha, L., Baker, J., Kathayat, G., Dong, X., Zong, B., Ning, Y., Zhang, H., and Cheng, H.: Control on millennial scale events (H-events) inferred from triple oxygen isotope ratios of speleothems from a Northeast Indian cave, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7701, https://doi.org/10.5194/egusphere-egu2020-7701, 2020.

Recent studies showed that the ¹⁷O-excess of plant leaf biogenic silicates (phytoliths) can be used to quantify the atmospheric relative humidity occurring during leaf water transpiration. The ¹⁷O-excess vs ∂¹⁸O signature of phytoliths can also be used to trace back to the signature of leaf water. In a similar way, the signature of lacustrine diatoms is expected to record the signature of the lake water in which they formed. Therefore, the triple oxygen isotope composition of biogenic silicates extracted from well-dated sedimentary cores may bring new insights for past climate and hydrological reconstructions. However, for high time-resolution reconstructions, we need to be able to measure microsamples (300 to 800 µg) of biogenic silica. In another context, the triple oxygen isotope composition of micro-meteorites constitutes an efficient tool to determine their parent-body. In this case too, micro-samples need to be handled.

Here we report the results of new ∂¹⁸O and ∂¹⁷O measurements of macro- and micro-samples of international and laboratory silicate standards (e.g. NBS28 quartz, San Carlos Olivine, Boulangé quartz, MSG phytoliths and PS diatoms). Molecular O₂ is extracted from silica and purified in a laser-fluorination line, passed through a 114°C slush to condense potential interfering gasses and sent to the dual-inlet Isotope Ratio Mass Spectrometer (IRMS) Thermo-Scientific Delta V. In order to get sufficient 34/32 and 33/32 signals for microsamples the O₂ gas is concentrated within the IRMS in an additional auto-cooled 800 ml microvolume tube filled with silica gel. Accuracy and reproducibility of the ∂¹⁸O, ∂¹⁷O and ¹⁷O excess measurements are assessed. Attention is payed to determine the concentration from which O₂ gas yields offsets in ∂¹⁸O, ∂¹⁷O and ¹⁷O-excess are measured and whether these offsets are reproducible and can be corrected for.

How to cite: Couapel, M., Sonzogni, C., Alexandre, A., and Sylvestre, F.: Accuracy and reproducibility of the triple oxygen isotope measurement of silicate micro-samples by laser-fluorination-IRMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14088, https://doi.org/10.5194/egusphere-egu2020-14088, 2020.

Oxygen isotopes are powerful proxies that are commonly used to decipher the formation of terrestrial and extraterrestrial rocks. Most of modern scientific approaches imply the determination of the oxygen isotopic composition at the mineral scale, thus requiring instruments enable to perform in situ, multi-collection, isotopic analyses in complex mineralogical assemblages and zoned minerals. Among them, large-geometry secondary ion mass spectrometer (LG-SIMS) is the most versatile with unique advantages such as (i) high spatial resolution (10–20 μm beam diameter and 1–2 μm depth); (ii) high sensitivity (detection limits below the ppm level for most elements) and (iii) high mass-resolution analysis allowing to remove most isobaric interferences (Villeneuve et al., 2019). Thanks to these capabilities, analytical uncertainties were significantly reduced for oxygen isotopes and reproducibilities much better that 1 ‰ on d¹⁷O and d¹⁸O are commonly obtained (e.g., Vacher et al. 2016; Marrocchi et al., 2018). Reaching such precisions is, however, linked to the use of 10¹¹ Ω Faraday Cups (FCs) that require minimum count rates of > 10⁶ cp/s for reaching permil precisions. This implies performing measurements with relatively large primary beam (i.e., 15-20 μm) that limits the minerals that can be targeted, especially in extraterrestrial samples (e.g., chondrule olivine crystals, Marrocchi et al., 2019).

Latest generation LG-SIMS instruments have been recently equipped with 10¹² Ω FCs that enable isotopic measurements to be performed at count rates significantly lower (i.e., 3 × 10⁵ cp/s) while maintaining good precision. This implies that high-precision oxygen isotopic measurements can be now performed with a less intense and smaller primary beam (~1 nA; 5 μm), In this contribution, we will report the specific characteristics of measurements using 10¹² Ω FCs and the reproducibilities obtained for oxygen isotope measurements. Few scientific examples where the use of 10¹² Ω FCs can represent a significant beakthrough will also be presented.

Marrocchi Y., Bekaert D.V. & Piani L. (2018). Origin and abundance of water in carbonaceous asteroids. Earth and Planetary Science Letters 482, 23-32.

Marrocchi Y., Euverte R., Villeneuve J., Batanova V., Welsch B., Ferrière L. & Jacquet E. (2019) Formation of CV chondrules by recycling of amoeboid olivine aggregate-like precursors. Geochimica et Cosmochimica Acta 247C, 121-141.

Villeneuve J., Chaussidon M., Marrocchi Y., Deng Z. & Watson B.E. (2019). High-precision silicon isotopic analyses by MC-SIMS in olivine and low-Ca pyroxene. Rapid Communication in Mass Spectrometry 33, 1589-1597.

Vacher L.G., Marrocchi Y., Verdier-Paoletti M., Villeneuve J. & Gounelle M. (2016) Inward radial mixing of interstellar water ices in the solar protoplanetary disk. The Astrophysical Journal Letters, 826, 1-6.

How to cite: Marrocchi, Y., Villeneuve, J., Peres, P., and Fernandes, F.: Recent developments and applications of triple oxygen isotope measurements by secondary ion mass spectrometry , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5798, https://doi.org/10.5194/egusphere-egu2020-5798, 2020.

Triple oxygen isotope data (denoted as ¹⁷O-excess) have been used to constrain meteorological processes, plant fractionation processes, animal metabolism, and a variety of other physical and chemical processes. Measurement precision is key in order to successfully apply this promising new tracer to a range of scientific questions. Up to date, the highest measurement precision for ¹⁷O-excess on water was achieved by converting water to O₂ and subsequent mass spectrometric analysis of O₂ (Barkan and Luz, 2005). This approach allows to reach a measurement precision of about 5-6permeg. However, it is very difficut to setup and only a few laboratories worldwide succesfully use this methodology. A far simpler approach is to use Cavity Ring-Down Spectroscopy (CRDS), i.e. the Picarro L2140-i analyzer that measures δ¹⁸O, δ¹⁷O, δD and determines ¹⁷O-excess. To date, the ¹⁷O-excess measurement precision of CRDS was limited to 10-15permeg. Here, we will present a new metholodology that allows to reach a similar or even better precision compared to the mass spectrometric approach. The improved methodology does not require any hardware changes but is solely based on modifications of the injection procedure. 

How to cite: Hofmann, M. E. G., Lin, Z., Doherty, T., Bent, J. D., and Lucic, G.: Improved precision and throughput for 17O-excess measurements on water with Cavity Ring-Down Spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20088, https://doi.org/10.5194/egusphere-egu2020-20088, 2020.

Can we not use the Δ value to measure a triple isotope system?

Huiming Bao^{1 ,2, 3} and Xiaobin Cao^{1 ,2}

¹ International Center for Isotope Effects Research, Nanjing University, Nanjing 210023, P. R. China

² School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, PR China

³ Department of Geology and Geophysics, Louisiana State University, E235 Howe Russell Kniffen, Baton Rouge, LA 70803

In a triple isotope system, taking oxygen for example, the deviation of the δ¹⁷O (or δ’) from a defined δ¹⁷O-δ¹⁸O relationship is measured by the term Δ, defined as the value of δ¹⁷O - C×δ¹⁸O, in which “C” is a reference slope number. The use of Δ has generated two problems. First, there is a spectrum of C values currently being adopted in the community, for reasons of end-member cases (e.g. 0.5305 at high-temperature limit), legacy (0.52), or compound-specificity (e.g. 0.528 for water cycle or 0.524 for silicates). These practices have brought confusions especially when we deal with small Δ values and when we must compare Δ values among different compounds. A second, more serious problem is the lack of appreciation that a Δ value scales with its corresponding δ¹⁸O value. That means even for the same process we may get different Δ values depending on the magnitude of fractionation and/or laboratory references used.

A pair of radial-angular parameters in a polar coordinate system or a pair of δ¹⁸O and δ¹⁷O in Cartesian space uniquely describe a triple isotope data point in 2D space. Either of the two ways would thaw any debates on the choice of reference slope value C necessary for calculating the Δ. In addition, a polar coordinate system is usually preferred when studying behaviors centering around an origin, in this case, isotope composition deviating from a reference point (0, 0). The angular coordinate φ of a triple isotope composition stays the same for the same fractionation process regardless of its radial coordinate r which is determined by δ¹⁸O and δ¹⁷O values. Thus, the use of a polar coordinate (r, φ) to describe a triple isotope composition in 2D space would avoid the δ¹⁸O scaling issue for Δ values of the same process. Unfortunately, polar coordinate does not offer straightforward representation of process-specific δs or fractionation factors. Using just a pair of δ¹⁸O and δ¹⁷O values to describe a triple isotope system also eliminates additional symbols. Unfortunately, the direct use of the δ¹⁸O and δ¹⁷O presents an apparently larger uncertainty for a data point than the other approaches. And it could not take advantage of the use of an accurate Δ value in case when the analytical yield is not 100%.

The limitations of a polar coordinate system or a pair of δ¹⁸O and δ¹⁷O in Cartesian space outweigh their advantages and we are left with no better alternative than the use of Δ. Therefore, when reporting small Δ values, we must report their corresponding δ¹⁸O values as well to avoid scaling bias when dealing with small Δ values.

How to cite: Bao, H. and Cao, X.: Can we not use the Δ value to measure a triple isotope system?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6191, https://doi.org/10.5194/egusphere-egu2020-6191, 2020.

Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. We have shown, through theoretical calculation and examining published data, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ¹⁷O) in olivine samples are not affected by crystallization and partial melting. This unique feature allows olivine Δ¹⁷O values to identify and quantify the fractions of subducted ocean sediments and hydrothermally altered oceanic crusts in OIB’s mantle source. In this work, new Δ¹⁷O measurements for OIB will be presented, and the implications will be discussed. 

How to cite: Cao, X., Bao, H., and Peng, Y.: Triple oxygen isotope constraints on the origin of ocean island basalts , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17738, https://doi.org/10.5194/egusphere-egu2020-17738, 2020.

Tracing the sources of pollutants in Ganga river water using conventional and non-conventional isotope analysis in nitrates

Abhayanand S. Maurya¹, Amzad H. Laskar², Nityanand S. Maurya³, Mao-Chang Liang⁴,

¹Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India

²Geosciences Division, Physical Research Laboratory, Ahmedabad 380009, Gujarat, India

³Department of Civil Engineering, National Institute of Technology Patna, India

⁴Institute of Earth Sciences, Academia Sinica, Taiwan

Ganga is the largest river in India providing fresh water to ~40 % of India’s population which is more than any other river in the world. It is also one of the most polluted rivers in the world. Pollution, mainly from human and industrial wastes in the Ganga poses significant threats to human health and environment. This is an attempt to identify and quantify the contribution of different sources in the river water pollution using stable isotopes in nitrate (NO₃^-). We measured non-conventional triple oxygen isotopes (∆¹⁷O_NO3=δ¹⁷O_NO3-λδ¹⁸O_NO3) along with the conventional isotopes (δ¹⁵N and δ¹⁸O) in NO₃^- and concentrations of major ions and metals (both heavy and trace ones) in Ganga river water to understand the sources and contribution from different pollution sectors. We also measured stable water isotopes (δD and δ¹⁸O) to understand the secondary processes such as in stream evaporation and inflow over the course of the river.  Water samples were collected from multiple locations starting from the clean water in the upstream region to all the way to the estuaries before the onset of monsoon, to best capture anthropogenic signals. ∆¹⁷O in NO₃^- is used to partition the atmospheric depositions from other sources such as human and industrial wastes and δ¹⁵N and δ¹⁸O values are used to partition the contribution of pollutants from different land sources such as municipal wastes and agricultural fertilizers. ∆¹⁷O in NO₃^- is also used to understand reaction processes which affect the isotopic composition such as nitrification, denitrification, volatilization, assimilation and mineralization as those processes mostly follow mass dependent fractionation without affecting ∆¹⁷O but influence the conventional isotopic compositions. We will present the results along with some recommendations for reducing the pollution level of the Ganga water.

How to cite: Maurya, A. S.: Tracing the sources of pollutants in Ganga river water using conventional and non-conventional isotope analysis in nitrates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2854, https://doi.org/10.5194/egusphere-egu2020-2854, 2020.

    High precision triple oxygen isotope measurement of meteoric water is a newly added tracer in hydrological and paleoclimate research. However, it is prerequisite to study the controls on precipitation ¹⁷O-excess for proper application of it. Here we report two years highly precise precipitation data from Nanjing, a southeast China station dominated by Asian monsoon. All the water isotopes (δ¹⁷O, δ¹⁸O and δD) reported here are based on mass spectrometer measurements and optical measurements (cavity ring-down spectroscopy). Nanjing receives moisture from different vapor sources and experiences different rainout mechanisms during various monsoonal sessions. Combined use of above parameters can help us to delineate processes occurring during evaporation, transport, condensation and re-evaporation. Year to year ¹⁷O-excess variability is observed in the obtained dataset and no notable seasonal variation is observed. However, the ¹⁷O-excess seasonal amplitude is little larger in the first year than the subsequent year. So far, it is known that the precipitation ¹⁷O-excess depends on three values: ¹⁷O-excess of the source water bodies, amount of ¹⁷O-excess gain during evaporation and ¹⁷O-excess loss during raindrops evaporation. During dry months ¹⁷O-excess gain is balanced by ¹⁷O-excess loss, which might lead to the near absence of seasonal cycle at Nanjing. From the comparison of observed data and model simulation, the amount of re-evaporation on falling raindrop is estimated to be about 10% at Nanjing. In addition, correlation with available meteorological parameters has been discussed. Except temperature no significant correlation has been found with other metrological variables (relative humidity and rainfall amount). This study will serve as a baseline to understand some of issues in paleoclimate that have puzzled the scientific community for years.

How to cite: Duan, P., Mahata, S., Sha, L., and Cheng, H.: Triple oxygen isotope variations in precipitation from southeast China and its hydrological significance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6734, https://doi.org/10.5194/egusphere-egu2020-6734, 2020.

Gypsum (CaSO₄∙2H₂O) speleothems (i.e. stalactites, stalagmites, etc.) in caves form frequently through dissolution of the gypsum host-rock by seepage water and subsequent secondary mineral re-precipitation from gypsum-saturated solutions [1]. Gypsum takes its structurally-bound hydration water (GHW) from the liquid; the isotopic composition (δ¹⁷O, δ¹⁸O and δ²H) of GHW reflects that of cave dripwater at the time of mineral crystallization, with insignificant effect of temperature on the liquid-GHW isotope fractionation factors [2]; therefore, GHW may be used to reconstruct the isotopic composition of paleo-dripwater in caves. Here we investigate the triple oxygen and hydrogen isotopic composition of GHW in speleothems from circum-Mediterranean gypsum caves, including the gypsum karsts of Emilia Romagna (NE Italy), Sorbas (SE Spain), Sicily and Mesaoria (Cyprus), all of them hosted in gypsum of Messinian age (ca. 5.5 Ma). The climatic settings of the studied caves range from semiarid (i.e. Sorbas and Mesaoria, <300 mm·yr^-1) to relatively wet (i.e. Emilia Romagna and Sicily >600 mm·yr^-1).

Our results reveal that most gypsum speleothems in these caves precipitated from unevaporated solutions (e.g. d-excess >8‰ and ¹⁷O_excess >10 per meg), with isotopic compositions similar to those of local meteoric/seepage waters and close to the local meteoric water lines (LMWL) of each region. Gypsum crystallization in absence of evaporation can be explained by the mechanism known as Ostwald ripening [3], a solution-mediated recrystallization under constant temperature by which older crystals (i.e. Messinian gypsum) dissolve to feed new crystals (i.e. gypsum speleothems). Only GHW in speleothems from the Sorbas caves show evidence for solution evaporation prior mineral precipitation. Gypsum speleothems in several caves of Emilia Romagna crystallized from unevaporated waters with significantly different triple oxygen and hydrogen isotopic compositions (e.g. Ca´ Castellina cave: δ¹⁸O=-8.3±0.3‰, δ²H=-55.2±1.7‰, ¹⁷O_excess=33±9 per meg; Abisso Bentini cave: δ¹⁸O=-10.6±0.3‰, δ²H=-73.4±1.8‰, ¹⁷O_excess=47±13 per meg). In absence of chronological data, this can be interpreted as (1) gypsum speleothems formed in different climatic periods or (2) do at present from waters that seepage into the epikarst during different times of the year. Either way, gypsum records the mean isotopic composition of seepage water under distinct environmental conditions in this region.

The δ¹⁸O and ¹⁷O_excess values across the entire dataset are negatively correlated, unlike δ¹⁸O and d-excess values that are, positively correlated for δ¹⁸O<-6‰ and negatively correlated for δ¹⁸O>-6‰. We suggest that the different behaviors of ¹⁷O_excess and d-excess derive from their distinct sensitivities to environmental parameters (i.e. RH and temperature) during formation of water vapor at the moisture source of rain and local effects during rainfall events in each area. We conclude that gypsum speleothems of known ages may be useful as archives for triple oxygen and hydrogen isotope reconstructions of paleo-rainfall.

[1] Gázquez et al. 2017. Chemical Geology, v. 452, p. 34–46; [2] Gázquez et al. 2017. Geochimica et Cosmochimica Acta, v. 198, p. 259–270; [3] Kahlweit, 1975. Advances in Colloid and Interface Science, v. 5, p. 1–35.

How to cite: Gazquez, F., Chiarini, V., Columbu, A., De Waele, J., Audra, P., Cailhol, D., Vattano, M., Madonia, G., Giesche, A., Calaforra, J.-M., and Hodell, D. A.: Gypsum speleothems record the triple oxygen (δ17O and δ18O) and hydrogen (δ2H) isotopic composition of cave dripwater: potential paleoenvironmental implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6938, https://doi.org/10.5194/egusphere-egu2020-6938, 2020.

Triple oxygen isotope compositions have become one of critical proxies in characterizing a wide range of geochemical and hydroclimate processes. However, Δ¹⁷O (carbonate ¹⁷O anomaly) has only been barely used in the last decade because it is difficult to measure δ¹⁷O of natural samples to a sufficient precision in order to resolve small natural variability. In this study, we present triple oxygen isotope data from speleothems obtained by an O₂-CO₂ Pt-catalyzed oxygen-isotope equilibration method. The high precision (9 per meg or better, 1σ SD) of our new speleothem Δ¹⁷O data is sufficient to resolve subtle hydroclimatic signals. Based on this method, we established triple-oxygen-isotope records of TON cave in westerly region since the last 135ka, providing the evolution history of water vapor source and water vapor cycle in the orbit-millennium scale atmospheric precipitation in the Central Asia. In addition, the triple-oxygen-isotope records of speleothem from Asian and South American monsoonal regions were established in the key periods, such as glacial and interglacial periods. Our speleothem Δ¹⁷O data indicate a 20 per meg difference between Marine Isotope Stage 5d and 5e in samples from Central Asia, suggesting a shift in moisture source and/or fractionation history. Unexpectedly, there were no measurable Δ¹⁷O differences between glacial and interglacial samples from both the South American (western Amazon) and Asian (southern China) monsoon domains, implying consistent moisture-source conditions across glacial and interglacial cycles, at least in terms of relative humidity. Speleothem Δ¹⁷O data may thus provide new and important constraints for understanding regional and global hydroclimate dynamics.

How to cite: sha, L., Mahata, S., Duan, P., Luz, B., Zhang, P., Baker, J., Zong, B., Ning, Y., Ait Brahim, Y., Zhang, H., Edwards, R. L., and Cheng, H.: A novel application of triple oxygen isotope ratios of speleothems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6791, https://doi.org/10.5194/egusphere-egu2020-6791, 2020.

Here, we describe a system for measuring triple oxygen and hydrogen isotopic ratios of both the liquid and vapour during evaporation of water in a dry gas stream (N2 or dry air) at constant temperature and relative humidity (RH).  The hardware consists of a polymer glove box (COY), peristaltic pump (Ismatec), and Picarro L2140-i cavity ring-down laser spectrometer (CRDS) with Standard Delivery Module (SDM). Liquid water from the evaporation pan is sampled via a closed recirculating loop and syringe pump that delivers a constant rate of water to the vaporizer, maintaining a constant concentration of water vapour in the cell (20,000 ±103, 1 s.d.) over an injection cycle. Liquid measurements alternate with vapour from the glove box which is introduced to the CRDS using a diaphragm gas pump. Important for high-precision measurements, both cavity pressure and outlet valve stability are maintained throughout the liquid injection and subsequent vapour phase. Experiments are bookended by two in-house standards which are calibrated to the SMOW-SLAP scales. An additional drift corrector is introduced periodically.

To test the precision and stability of the liquid injections, we sampled from an isotopically homogeneous volume of water and introduced it to the cavity over a period of ~48h. To minimise the standard deviation derived from noise, we chose an optimum integration time of ~2000s (~33 minutes) based on σ_Allan minimisation. Therefore, for combined liquid-vapour experiments we use an injection/vapour sampling window of 40-minutes (140ug water is consumed per injection), which provides a data collection period of 33-minutes after a 7-min waiting time for equilibration.

Across a single liquid injection, the mean standard error for d¹⁷O, d¹⁸O, and dD is 0.008‰, 0.007‰, and 0.02‰, respectively. For the vapour phase equivalent, the mean standard error for d¹⁷O, d¹⁸O, and dD is 0.01‰, 0.009‰, 0.03‰ respectively. For the d-excess in the liquid and the vapour across one 33-minute cycle, the standard error is 0.07‰ and 0.08‰, respectively. For the O17-excess in the liquid and the vapour across one 33-minute cycle, the standard error is 6 per meg and 8 per meg, respectively.

A single evaporation experiment produces in excess of 100,000 measurements each of d¹⁷O, d¹⁸O, and dD for both the evaporating liquid and resulting vapour. These measurements result in 95% confidence limits for the slope of ln(d¹⁷O+1) vs ln(d¹⁸O+1) of ±0.0002 and ±0.0003 for the liquid and vapour, respectively.  For the slope of ln(dD+1) vs ln(d¹⁸O+1) we obtain a 95% confidence interval of ±0.001 and ±0.002 for the liquid and vapour, respectively. The experimental method permits measurement of fractionation of triple oxygen and hydrogen isotopes of water under varying experimental conditions (e.g., RH, temperature, turbulence) at very high precision. It will be useful for testing numerical models of evaporation and conducting experiments to simulate evaporation and isotopic equilibration in natural systems. An application to closed-basin lakes will be presented.

How to cite: Brady, M. and Hodell, D.: Continuous and simultaneous measurement of triple oxygen and hydrogen isotopes of liquid and vapour during evaporation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16872, https://doi.org/10.5194/egusphere-egu2020-16872, 2020.

The Thar Desert (NW India) has numerous evaporative saline playa lakes. Some are still active and others are dry and preserve up to several meters of sedimentary deposits. These deposits feature a variety of evaporite minerals, including the hydrated mineral gypsum (CaSO₄ 2H₂O). Assuming no secondary exchange, the isotopic composition of the gypsum hydration water preserves the δ¹⁸O, δ¹⁷O and δ D of palaeolake water at the time of gypsum formation. This method provides a way to understand the hydrologic balance in a part of the world where it is typically very difficult to obtain palaeoclimate records. Our 36-hour pan evaporation experiment on site shows that triple oxygen isotopes track changes in evaporative conditions, which vary diurnally due to fluctuating temperature and relative humidity, and appear to reflect night-time condensation. We present new palaeohydrological records from two dry playas (Karsandi, Khajuwala) and one active playa (Lunkaransar) in the Thar Desert using the triple oxygen and hydrogen isotopic composition of gypsum hydration water. Results show that a source of water maintained active playa lake basins in the central Thar Desert for much of the Holocene, either by enhanced direct precipitation and/or fluvial sources. The derived ¹⁷O-excess and d-excess data potentially enable modelling of past changes in relative humidity, once other parameters (windiness, evaporation/inflow, etc.) are set.

How to cite: Giesche, A., Dixit, Y., Gázquez, F., Bauska, T., Brady, M., Singh, V. K., Singh, R. N., Petrie, C. A., and Hodell, D. A.: A paleoclimatic perspective of triple oxygen isotopes from gypsum in Holocene Thar Desert playa lakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21681, https://doi.org/10.5194/egusphere-egu2020-21681, 2020.

This study reports on measurements of Δ¹⁷O (derived from the triple oxygen isotopes) in sulphate from black crust sampled in Sicily. Atmospheric oxidants, such as O₃, H₂O₂, OH and O₂ carry specific ¹⁷O-anomalies, which are partly transferred to the sulphate during sulphur gas (e.g. SO₂) oxidation. Hence, the Δ¹⁷O in sulphate can be used as a tracer of sulphur oxidation pathways. So far, this method has been mostly applied on sulphate from aerosols, rainwaters, volcanic deposits and ice cores. Here we propose a new approach, that aims to investigate the dominant oxidants of gaseous sulphur precursors into sulphate extracted from black crust material. Black crusts are mostly found on building/monument/sculpture and are the result of the reaction between sulphur compounds (SO₂, H₂SO₄) and carbonate (CaCO₃) from the substrate, which leads to the formation of gypsum (CaSO₄, 2H₂O). Sicilian black crust from sites under different emission influences (anthropogenic, marine and volcanic) were collected. Multi oxygen and sulphur isotope analyses were performed to better assess the origins of black crust sulphate in these different environments. This is crucial for both a better understanding of the sulphur cycle and the preservation of historical monument.

Multi sulphur isotopes show mostly negative values ranging from -0.4 ‰ to 0.02 ‰ ± 0.01 and from -0.59 ‰ to 0.41‰ ± 0.3 for Δ³³S and Δ³⁶S respectively. This is unique for natural samples and different from sulphate aerosols measured around the world (Δ³³S > 0‰). This tends to indicate that sulphate from black crust is not generated by the same processes as sulphate aerosols in the atmosphere. Instead of SO₂ oxidation in the atmosphere, dry deposition of SO₂ and its oxidation on the substratum is preferred. The multi oxygen isotopes show a clear dependence with the geographical repartition of the samples. Indeed, black crusts from Palermo (the biggest Sicilian city) show small ¹⁷O-anomalies ranging between -0.16 ‰ to 1.02 ‰ with an average value of 0.45 ‰ ± 0.26 (n=12; 2σ). This is consistent with Δ¹⁷O values measured in black crust from the Parisian Basin (Genot et al., 2020), which are also formed in an environment influenced by anthropogenic and marine emissions. On the other hand, samples from the eastern part of the Mount Etna region, which are downwind of the volcanic emissions, show the highest ¹⁷O-anomalies ranging from 0.48 ‰ to 3.87 ‰ with an average value of 2.7 ‰ ± 0.6 (n=11; 2σ).

These results indicate that volcanic emissions influence the oxygen isotopic signature of black crust sulphate. In standard urban areas, SO₂ deposited on the substratum is mostly oxidised by O₂-TMI and H₂O₂ to generate the black crust. Yet, under the influence of volcanic emissions, O₃ may play the main role in the SO₂ oxidation.

How to cite: Aroskay, A., Martin, E., Bekki, S., Montana, G., Randazzo, L., and Cartigny, P.: The multi oxygen isotope analyses on black crust from Sicily highlight the volcanic emission influence from Mount Etna on urban areas , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20136, https://doi.org/10.5194/egusphere-egu2020-20136, 2020.

The earliest known physical records of Mars and Earth lie in microscopic grains of zirconium-rich geochronology minerals such as zircon and baddeleyite. The reconstruction of the pressure and temperature histories of these phases is one of the few ways in which we can bracket the onset of conditions permissive of microbiota survival, and requires an integration of several nanoscale measurement techniques. This presentation will overview a recent, detailed investigation of zircons and baddeleyite from Mars [1], the earliest known from planets to date, as well as comparator studies of thermally and/or shock metamorphosed samples from the Earth and Moon. The approach is to spatially correlate measurements of the chemical and orientation microstructure of individual grains in order to characterize thermal, shock and diffusion history and better interpret U-Pb geochronology data. Also revealed are proxies for high temperature metamorphism such as nanoclusters of Pb and trace elements and nanoveins of impact melt as well as trace elements introduced through subsequent lower-temperature hydrothermal metamorphism. The techniques required include electron microscopy and cathodoluminescence (CL), Electron Backscatter Diffraction (EBSD), Transmission Kikuchi diffraction (TKD), mass spectrometry, and Atom Probe Tomography (APT). The Mars records were collected from a population of zircon and baddeleyite grains within five meteoritic fragments of polymict breccia (e.g. NWA 7034, NWA 7475). These data were compared to those from analogue sites of heavily bombarded Archean crust such as the central uplift of the Vredefort structure of South Africa, the Earth’s largest and oldest recognized impact crater, the Sudbury impact structure in Canada, and Apollo samples of the lunar regolith. The Mars population of grains reveals little evidence of the nanofeatures of heavily bombarded and heated crust, and no exposure to life-limiting pressures or temperature since crystallization 4.48 billion years ago. The conclusion is that global, planet-shaping bombardment effects on Mars, such as those which created its distinctive hemispheric dichotomy, had ceased by the time these grains and their associated crust crystallized. It follows that Mars entered a window of habitable conditions very early in solar system history, a pathway likely mirrored by the Earth. In this way nanoscale measurements, required to investigate microscopic mineral grains, serve as important tools for reconstructing important time periods in planetary evolution and abiogenesis.

Reference:

[1] DE Moser, GA Arcuri, DA Reinhard, LF White, JR Darling, IR Barker, DJ Larson, AJ Irving, FM McCubbin, KT Tait, J Roszjar, A Wittmann, C Davis (2019) Decline of giant impacts on Mars by 4.48 billion years ago and an early opportunity for habitability. Nature Geoscience 12,  522–527.

How to cite: Moser, D.: Dating habitability with nanoscale measurements of Early Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11454, https://doi.org/10.5194/egusphere-egu2020-11454, 2020.

The field of planetary mineralogy has greatly benefited from recent studies of accessory minerals that utilise µm- and nm-scale analytical techniques such as EBSD, APT, TEM and SIMS. Apatite and merrillite have been of particular interest, as they record vital information on the volatile content, U-Pb ages and trace-element composition of various planetary materials. However, the extent to which shock-deformation, pervasive among all planetary materials, affects the distribution of these valuable geochemical tracers is still poorly understood. Here we focus on exploring the U-Pb and Pb-Pb ages of apatite and merrillite in a set of variably shocked lunar rocks, building on previous nanostructural analyses of the phosphates.

We carried out U-Pb and Pb-Pb analyses of phosphates in Apollo 17 samples of the Mg-suite rocks (76535, 76335, 76255, 72255, 78235 and 78236) using the CAMECA 1280 ion microprobe at the NordSIMS facility (Stockholm). In addition, we applied a recently developed approach of conducting high-precision U-Pb and Pb-Pb analyses by ID-TIMS of extracted phosphate grains (Jack Satterly Lab, University of Toronto). For this purpose, individual ~50x50x30 µm crystals of apatite and merrillite were extracted directly from thin sections using a Xe⁺ plasma FIB.

As determined by SIMS, ²⁰⁷Pb/²⁰⁶Pb systematics of the unshocked or weakly shocked apatite in 76535 and 76335 is undisturbed, implying cooling of the rock below the closure temperature of Pb diffusion in apatite (~450°C) at ~4.2 Ga, ~100 Ma younger than what is interpreted as the rock’s crystallization age. Phosphates that experienced similar levels of deformation but were in proximity or in direct contact with the impact melt in samples 76255 and 72255 show almost complete age resetting (~3.92 Ga). The SIMS determined age of 16 phosphates in sample 76255 is 3922.2 ± 6.7 Ma (2σ) and agrees with the previously published ²⁰⁷Pb/²⁰⁶Pb phosphate ages of impact melt breccias found within the same boulder and was interpreted as the timing of the Imbrium impact. These recrystallized phosphates yield comparable TIMS Pb-Pb ages (3917.8 ± 1.8 Ma and 3921.0 ± 1.3 Ma, 2σ) with significantly lower internal uncertainties than that of the individual SIMS measurements and may represent multiple impact-events close to the Imbrium event.

SIMS U-Pb analyses of highly shocked phosphates (78235 and 78236) reveal a discordia line with an upper intercept of ~4.2 Ga and a lower intercept of ~0.5 Ga. We interpret this new, younger age as a minor thermal event that reactivated existing shock-induced nm-scale grain boundaries, as visualised by APT, within the apatite population to allow for Pb-loss at ~0.5 Ga. We propose a small crater located near the Apollo 17 landing site as a possible source of this sample.

By correlating micro- to nanostructural characterization with in-situ age systematics we show that apatite and merrillite are powerful thermochronometers that provide a new approach to dating which has the potential to discriminate between temporally similar events. This can greatly aid in unravelling the bombardment record of solar system and be helpful when dealing with samples of limited availability (e.g. space return missions).

How to cite: Cernok, A., White, L., Tait, K., Anand, M., Kamo, S., Whitehouse, M., and Darling, J.: Lunar Phosphates Record Impact Cratering Events at Micro to Nano Scales , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1169, https://doi.org/10.5194/egusphere-egu2020-1169, 2020.

Clinopyroxenes (Na,Mn,Ca,Fe²⁺)_1-2(Mg,Al,Cr,Fe³⁺)_1-2[(Al,Si)₂O₆] are common inclusions in natural diamonds of either peridotitic or eclogitic paragenesis. The variety of the composition of pyroxene inclusions in diamonds records the chemical and the physical conditions of the mantle. New approach based on Raman spectroscopy data on 43 pyroxene inclusions in diamonds from Yakutian province (the Siberian craton) and their chemical analyses are provided in this study.

Raman spectroscopy is a high-resolution and non-destructive method used to detect the compositional and the structural characteristics of materials and minerals including high-pressure crystal inclusions in diamonds. Raman spectra of clinopyroxene inclusions in diamonds were collected by Horiba LabRAM HR800 Raman spectrometer with 532-nm laser. In addition, the compositional analyses were obtained by EPMA (JEOL JXA-8100) to correlate chemical variations with specific spectral features and Raman shifts.

Clinopyroxene inclusions show variations of chemical content in the wide ranges: SiO₂ 54.1-55.9 wt.%, Al₂O₃ 0.31-4.11 wt.%,  Cr₂O₃ 0.32-5.73 wt.%, FeO 1.81-3.49 wt.%, MgO 13.4-18.3 wt.%, CaO 16.1-22.9 wt.%, Na₂O 0.28-3.82 wt.% for peridotitic type and SiO₂ 52.4-56.8 wt.%, Al₂O₃ 4.46-17.8 wt.%,  Cr₂O₃ <0.29 wt.%, FeO 2.22-11.4 wt.%, MgO 5.65-15.1 wt.%, CaO 9.81-17.1 wt.%, Na₂O 3.118-8.121 wt.% for eclogitic type.

Generally, the inclusions yield Raman spectra with four high-intense modes (ν₃, ν_3’, ν₄, ν₁₁, ν₁₇). Observed relative intense of most of these modes (except ν₁₁) depend on changing of crystal orientation. The ν₁₁-mode belongs to the Si-O stretching vibrations of bridging oxygen atoms (Si-O_br). The recorded position of this mode varies in the ranges 665.6-675.1 cm^-1 for peridotitic type inclusions and 673.7-688.2 cm^-1 for eclogitic type inclusions. One of the factors controlling the shifts of position frequencies of n11-mode is composition.

Peridotitic clinopyroxenes display strong linear correlations between the shifts of position of the ν₁₁-mode and contents of Al₂O₃ (correlation coefficient r = 0.94), FeO (correlation coefficient r = 0.68), MgO (correlation coefficient r = -0.52), CaO (correlation coefficient r = -0.69), Na₂O (correlation coefficient r = 0.92). Eclogitic clinopyroxenes show linear correlations between the shifts of position of the n₁₁-mode and contents of Al₂O₃ (correlation coefficient r = 0.95), FeO (correlation coefficient r = -0.64), MgO (correlation coefficient r = -0.85), CaO (correlation coefficient r = -0.59), Na₂O (correlation coefficient r = 0.84). The most expressed correlations can be used for estimation of composition of inclusions in diamonds only by Raman spectroscopy data without destruction of diamond-host and for identification of clinopyroxenes from potentially diamondiferous mantle rocks.

Acknowledgments: Russian Science Foundation (16-17-10067) supported this work.

How to cite: Kalugina, A. and Zedgenizov, D.: The Raman Estimation of the Composition of Clinopyroxene Inclusions in Natural Diamonds , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-826, https://doi.org/10.5194/egusphere-egu2020-826, 2020.

Indium-bearing sphalerites from the Hämmerlein skarn deposit, located in the western Erzgebirge (Germany), show complex distribution patterns of major and minor elements on a micrometer to sub-micrometer scale. However, with the spatial resolution of traditional analytical methods, such as SEM-based image analysis and field emission electron probe microanalysis (FE-EPMA), many features in these spalerites cannot be resolved. It remains unclear whether Cu, In and Fe are in solid solution in the sphalerite, are concentrated in nanoparticles or form discrete phases.

Atom probe tomography combined with transmission kikuchi diffraction has been used to resolve both the compositional heterogeneity and the nanostructure of these complex In-Cu-Fe-sphalerites. The obtained data indicate a complex structure with micro- to nanometer sized, plate-shaped inclusions of chalcopyrite in the sphalerite. In addition, a nanometer scale In-Cu-sulfide phase forms plate-like segregations in the sphalerite. All types of segregations have similar crystal structure and record the same crystal orientation indicating that they likely formed by exsolution.

The results indicate that complex sulfides containing cations of more than one element as minor or major constituents may represent discrete, exsolved phases, rather than solid solutions or being concentrated in nanoparticles. This heterogeneous nature will affect the nanoscale properties of the sphalerite, which may have implications for the economic extraction of precious elements such as In, when processing these minerals for beneficiation. Furthermore these nanoscale properties will open up new perspectives on formation processes of In-Cu-Fe-sphalerites, which might be relevant for other chemically complex minerals as well.

How to cite: Krause, J., Reddy, S. M., Rickard, W. D. A., Saxey, D. W., Fougerouse, D., and Bauer, M. E.: Nanoscale compositional segregation in complex In-bearing sulfides: Results from atom probe tomography and transmission kikuchi diffraction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3473, https://doi.org/10.5194/egusphere-egu2020-3473, 2020.

Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS), operating in multicollection mode, allows high precision light isotope ratio measurements at high lateral resolution (tens of μm down to sub-μm range). For some challenging applications involving fine scale analysis of low abundance isotopes (i.e. ¹⁷O or ³⁶S) or low-concentration elements (i.e. nitrogen in diamonds) measurement of low signal intensities is required. Traditionally, count rates between the upper level of pulse counting systems ~10⁵ c/s and the lower level of Faraday Cup (FC) measurements ~10⁶ c/s are considered to be in a “gap area” where neither detection protocol can achieve performance better than the 1‰ level.

Faraday Cup detectors (FC) offer high precision with no need for gain monitoring, however the uncertainty of FC measurements depends on the signal to noise ratio. One approach for measuring low signal intensities is to use FCs coupled to electrometers with high ohmic resistors. CAMECA LG-SIMS can now be equipped with low noise 10¹² Ω resistor FC preamplifier boards for measuring signal intensities down to the ~ 3 x 10⁵ c/s range with precision better than the 0.5‰ level (1SD).

For measurement of low-abundance isotopes, a complementary approach consists of using discrete-dynode pulse counting electron multiplier (EM) detectors, for which drift and aging effects are minimized using a fast automated EM high voltage adjustment routine.

During this PICO presentation, we will discuss the relevance of the detector choice (FC 10¹² Ω vs EM) for few examples of innovative applications.

Example of mass independent fractionation:

In addition to classical isotopic ratio measurements (e.g. δ¹³C, δ¹⁵N, δ¹⁸O or δ³⁴S), for which the instrumental mass fractionation (IMF) correction is mostly limited by the natural heterogeneity (chemical and isotopic) of the reference material, SIMS is particularly well suited for the measurement of mass independent fractionation (MIF, e.g. ∆³³S, ∆³⁶S and ∆¹⁷O). Along with classical geochemical processes, the degree of isotopic fractionation scales with the difference in mass of the isotopes involved (i.e. δ³³S ≈ 0.515 * δ³⁴S). MIF refers to non-conventional ratios that depart from these mass dependent rules. As instrumental mass fractionation has been shown to be strictly mass dependent, MIF measurements are not subject to IMF correction and are therefore measured directly. The use of SIMS in this specific case is particularly well suited and allows to fully explore the rich phenomenology of MIF source processes. We will discuss the advantages and disadvantages of using FC 10¹² Ω for the minor Sulphur isotope (³⁶S) measurement.

Carbon and Nitrogen in diamond:

We will also show a recent analytical development aiming to measure δ¹³C in diamonds at mass resolution of ~5000 (allowing the full separation of ¹³C- and ¹²CH-) as well as N-content and N-isotopes in diamonds at a mass resolution of ~9000 (full separation of ¹²C¹⁴N- and ¹³C¹³C-).  For this purpose, the use of FC 10¹² Ω greatly improves the data quality and allows the simultaneous measurement of N-content and δ¹⁵N.

How to cite: Peres, P., Thomassot, E., Deloule, E., Bouden, N., and Fernandes, F.: Innovative Detection Strategies on Large Geometry SIMS open new challenging applications for light isotope ratio analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20427, https://doi.org/10.5194/egusphere-egu2020-20427, 2020.

Natural and synthetic iron oxides and iron hydroxides are important minerals for many industrial sectors (e.g. steel making, colors, pigment for coating, electronics, catalysis, soil, waste water and gas treatments, and medicine). In natural environments, such as iron ore mines or iron rich soils (laterites or bauxites), iron oxy-hydroxide associations are complex and evolve related to varying physico-chemical conditions, including. biological interactions. For efficient resource use, unambiguous multiscale characterization is indispensable. Synthetic iron oxides, produced for medical and electronic sector, needs to be failure-free pure phases, thus a continuous quality control is required. Complex iron oxy-hydroxide association can be related to various processes, topotactic transition, pseudomorphosis by substitution and alteration paramorphosis, and corrosions, leading to massive, porous, fibrous and acicular textures or poorly crystalline crusts.

We present examples from iron ore deposits, where coupling of X-Ray diffraction (XRD) with scanning electron microscopy (SEM) and micro-Raman spectroscopy is a powerful tool to distinguish hematite, maghemite and magnetite at grain scale. Oxygen analyses by electron microprobe at (EMPA) fixed carbon coating thickness help to distinguish magnetite and hematite, and contribute with quantitative trace element analyses to chemically differentiate both oxides. At micro- and nano-scale, Transmission Electron Microprobe analyses coupled to X-Ray Diffraction (XRD) and Electron Energy Loss Spectroscopy (EELS) on nanometric inclusions can unambiguously identify various iron oxy-hydroxide phases. In Nickel-laterite and bauxite profiles, iron oxy-hydroxides (e.g. lepidocrocite, ferrihydrite, goethite…) are abundant and may form complex intergrowth with various types of phyllosilicates. Part of it host valuable metals such as Nickel. Combined XRF-XRD and Raman spectroscopy allow phase mapping and differentiation at micron scale of these phases, and even detect solid solutions (e.g. Ni-rich and Ni-poor goethite; El Mendili et al., 2019). Results from coupled laboratory analyses are necessary for building up data bases. They allow calibrating recently developed combined XRF-XRD-Raman benchtop systems. For industrial applications coupled and combined analyses will increase resource efficiency, and ensure a quality control for natural and synthetic iron oxide products. Such systems are recently developed by EU projects, such as SOLSA (www.solsa-mining.com).

El Mendili, Y., Chateigner, D., Orberger, B., Gascoin, S, Bardeau, JF., Petit, S., Le Guen, M., Pillière, H. (2019). Combined XRF, XRD, SEM-EDS, and Raman analyses on serpentinized harzburgite (Nickel Laterite Mine, New Caledonia): Implications for Exploration and Geometallurgy. ACS Earth and Space Chemistry. 3, 10, 2237-2249; DOI: 10.1021/acsearthspacechem.9b00014

How to cite: Orberger, B., Wagner, C., El Mendili, Y., Chateigner, D., Gascoin, S., Pillière, H., Fialin, M., Rividi, N., Boudouma, O., and Wirth, R.: Coupled and combined analyses for unambiguous iron-oxy hydroxides characterization: from laboratory to industrial use , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2019, https://doi.org/10.5194/egusphere-egu2020-2019, 2020.

Quantitative modal analysis of rock thin sections or liberation analysis of minerals processing plant materials can be very complex as grain sizes can vary by more than 7 orders of magnitude: Thin sections of rocks may contain extremely coarse grains (mm-sized crystals) down to glassy material with no long-range order (ordered domains <1 nm).

Material characterisation and modal analysis have traditionally been carried out with a combination of solid-state, microscopic and spectroscopic techniques (e.g., optical / scanning electron microscopy, powder X-ray diffraction, X-ray fluorescence spectroscopy). These techniques require different sample preparation routines, data acquisition and evaluation - a time-consuming process that may be considered too complex to implement in mineral processing plants despite requiring the relevant sample preparation equipment. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS provides an opportunity to carry out this characterisation in a more rigorous and, in certain cases, automated way. This process includes image thresholding (setting of grey levels of present phases by the analyst) and X-ray data collection with EDS. EDS is an ideal analytical technique for this work as it offers high acquisition speeds and the collection of the whole energy spectrum with a single detector, not requiring the selection of a fixed element list prior to data acquisition. Characterisation of coarse-grained rocks requires larger areas to be scanned in order to ensure representativity.

The analytical workflow can be further optimised by combining SEM-based analytical techniques for in situ, non-destructive, and potentially simultaneous bulk analysis. Electron backscatter diffraction (EBSD) is an SEM-based technique which can be used to determine the crystallographic properties and orientation of mineral grains, as well as to perform fabric analyses on polycrystalline materials. EBSD allows for crystallographic data to be collected simultaneously with chemical data and does not require powdered samples. As a result, the texture of the material can be fully preserved. The sample preparation requirements of the technique are similar to those for standard SEM-EDS, with an additional final polishing step, essential for the removal of surface imperfections, as the EBSD signal is generated on the sample surface. The coupling of EDS and EBSD datasets permits the enhanced interpretation of feature analysis data, allowing for a deeper understanding of the compositional, structural and textural properties of the sample. This, highly-efficient, in-situ, bulk material characterisation, is key for the mining industry, as it provides insights for optimising downstream procedures thereby saving time and resources and bolstering throughput and efficiency.

How to cite: Stavropoulou, A., Hiscock, M., Kamber, B., and Rodriguez-Blanco, J.-D.: Combining SEM, EDS & EBSD: Challenges and considerations in the micro-analysis of rock thin sections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3941, https://doi.org/10.5194/egusphere-egu2020-3941, 2020.

The laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) is a unique method for local analysis that allows studying mineral grains in situ. The aims of these geochemical researches are to estimate concentrations and distributions of REE, Hf, U, Th, Y, Ti, PGE and other elements in accessory and ore minerals from complex deposits in the Arctic region (Fennoscandian Shield), using the LA-ICP-MS local analysis of trace elements. Accessory minerals of zircon and baddeleyite are much valued to study distributions of rare and rare earth elements (REE). Besides, pyrite, pentlandite, pyrrhotite and other sulfides are important for determining platinum-group elements (PGE), REE, etc.

The electron (LEO-1415) and optic (LEICA OM 2500 P, camera DFC 290) spectroscopy have been applied to study the morphology of the samples. Analytical points have been selected on baddeleyite, zircon crystals and sulfide minerals based on analyses of their BSE, CL and optical images. REE, PGE and other elements have been estimated in situ by ICP-MS, using an ELAN 9000 DRC-e (Perkin Elmer) quadrupole mass spectrometer equipped with UP-266 MAСRO laser (New Wave Research).

More than 19 elements were profiled during each measurement in zircon or baddeleyite. For the first time, LA-ICP-MS techniques have been applied to estimate PGE, REE and other (S, Cr, Fe, Cu, Ni, Co, As, Se, Mo, Cd, Sn, Sb, Re, Te, Tl, Hf, W, Bi, Pb, Th, U) elements in sulfide minerals. NIST 610, NIST 612 and tandem graduation (using solutions), considering sensitivity coefficients of isotopes have been used to check the accuracy of estimations. Fe, Ni and Cu have been used as internal standards, being most evenly distributed elements in minerals, when concentrations of elements in sulphides were calculated. The estimates have been carried out, using inter-laboratory standards of chalcopyrite, pentlandite and pyrrhotite, which had been preliminarily prepared and studied using micro probe analysis (Cameca MS-46).

These techniques had been used to estimate elements in zircon extracted from basic and acidic rocks of the Lapland belt (1.9 Ga), the Keivy zone (2.7 Ga), the Kandalaksha and Kolvitsa zone (2.45 Ga) and from the Cu-Ni deposit (Terrace, Mt. Nyud, 2.5 Ga). Novel techniques have been used to analyze baddeleyite from rocks of layered PGE intrusions of the Monchegorsk ore area (2.5 Ga) and carbonatites of Kovdor and Vuoriyarvi (380 Ma). Elaborated LA-ICP-MS techniques have been applied to provide in situ measurements of PGE, Au, Ag, siderophile and chalcophile elements in sulphide minerals from the Pechenga and Allarechka Cu-Ni deposits (1.98 Ga), Fedorova Tundra and Severny Kamennik PGE deposits (2.5 Ga).

The scientific researches are supported by RFBR Grant No 18-05-70082, scientific themes 0226-2019-0032 and 0226-2019-0053.

How to cite: Drogobuzhskaya, S., Bayanova, T., and Novikov, A.: Geochemical researches in situ (LA-ICP-MS) of accessory and ore minerals from multimetal (PGE, Cu-Ni) deposits in the Arctic zone (Fennoscandian Shield) of the Russian Federation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13123, https://doi.org/10.5194/egusphere-egu2020-13123, 2020.

The Scanning Electron Microscope (SEM) is the most prolific piece of analytical equipment in the Earth Sciences, therefore quantitative mineral chemistry obtained directly from the SEM has the potential to streamline many geological fields. Mineral chemistry provides direct constraints on geological processes that are used in a wide variety of Earth Science disciplines. As a result, major element analysis of rock forming minerals have been one of the major contributors to geochemistry for decades. Electron beam techniques have been the most widely used method of obtaining in situ major element chemistry, dominated by the quantitative Wavelength Dispersive Spectroscopy (WDS) employed by the Electron Probe Micro Analyser (EMPA). More rapid, and typically more qualitative Energy Dispersive Spectroscopy (EDS) major element measurements are often obtained on a standard SEM instrument.

The relative simplicity of the EDS technique saw the growth of automated mineralogy systems beginning in the 1980’s. The peaks of EDS spectra are characteristic of the major elements present, and therefore lookup tables can be used to match the spectra to known mineral compositions and provide a likely mineralogy in both grain mounts and mapped thin sections. The automated mineral analysis technique remained essentially unchanged for decades, with an experienced operator required for many of the analytical tasks, such as creating the files for matching spectra to known minerals, processing the data, and interpreting complex phases and solid solutions (e.g. Fe/Mg-bearing silicates).

The ZEISS Mineralogic automated quantitative mineralogy (AQM) takes a new approach, using EDS detectors, but following an analytical protocol more closely aligned with EPMA. A combination of matrix corrections, peak deconvolution, and standard calibration means that peak intensities are converted directly into wt% element directly at the time of analysis. The result is a data output that can be immediately interpreted, even for minerals not previously analysed, by both new and experienced users.

Here we demonstrate the use of the ZEISS Mineralogic system for mapping thin sections from high grade metamorphic rocks. The bulk chemistry of the entire thin section, as well as individual mineral compositions can be used to constrain P-T conditions directly from the SEM, without the need for an additional step of obtaining mineral chemistry from an EPMA. With quantitative analysis at every pixel, major element profiles can be obtained at any point in the thin section, and P-T can therefore be determined from any domain within the mapped section. This approach makes the use of P-T pseudosections possible with greater speed and flexibility than has previously been possible.

How to cite: Taylor, R., Hill, E., Lanari, P., Clark, C., and Johnson, T.: Quantitative automated mineralogy to constrain metamorphic processes using ZEISS Mineralogic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14000, https://doi.org/10.5194/egusphere-egu2020-14000, 2020.

Over the past two decades, laser ablation coupled with the mass spectrometer has become a major analytical tool for the measurement of isotopic ratios and the determination of trace elements. The improvement of the sensitivity has provided new perspectives and permits to study new types of targets. For example, many questions remain open about the formation of supergene mineralization such as: what is exact timing for their deposition? What are the required associated physico-chemical conditions? To answer these questions, we focused on two copper deposits located in Chile (Mina Sur) and Burkina Faso (Gaoua) to develop U-Pb analysis and trace element profiles in pseudomalachite and chrysocolla. The analyses were carried out at the GET Laboratory (Toulouse). Different couplings between a femtosecond laser (fs-LA) or a nanosecond laser (ns-LA) and a HR-ICPMS or a MC-ICPMS were used. Trace elements determination and in situ U-Pb analysis present different challenges. For U-Pb analyses, matrix effects must be taken into account and the contribution of common lead (²⁰⁴Pb) must be subtracted. As there is no chrysocolla or pseudomalachite reference materials, zircon and apatite were used as the primary external standards and fs-LA was used as a matrix independent sampling method. No significant U-Pb fractionation was observed, whatever the structure of the ablated matrix (silicate, phosphate). The bias linked to common lead was calculated from fs-LA-MC-ICPMS measurements. The ²⁰⁶Pb / ²⁰⁴Pb intensity ratio gives a first approximation on the possibility to determine the U-Pb age. Three cases have been distinguished: 1) If ²⁰⁴Pb is low (²⁰⁶Pb / ²⁰⁴Pb ≥ 500) the U-Pb age obtained by this first analyze can be used. 2) If ²⁰⁴Pb is significant and the intensity ratio of ²⁰⁶Pb / ²⁰⁴Pb range between 500 and 5, a second step is necessary. In such a case, ²⁰⁴Pb must be determined more precisely using a MC-ICPMS to retrieve the common lead corrected U-Pb age. 3) If ²⁰⁴Pb is high (²⁰⁶Pb / ²⁰⁴Pb <5), then it is not possible to determine the U-Pb age of the sample. Trace element profiles were also performed on the same chrysocolla and pseudomalachite samples. These analyses have been carried out using a ns-LA coupled to HR-ICPMS and NIST SRM 610 was used as primary standard. The reproducibility and accuracy of the analyses were verified by the ablation of secondary standards (91500 zircon and Durango apatite) and comparison with EMPA analyses. In this study we demonstrate that supergene mineralization can be directly dated and the trace elements in pseudomalachite and chrysocolla can be determined. The combination of these methods provides a new tool to understand the physico-chemical and geological conditions that are required for the formation of supergene mineralization.

How to cite: Leisen, M., Kahou, Z. S., Brichau, S., Duchêne, S., d’Abzac, F.-X., and Choy, S.: U-Pb in situ dating and trace elements profiles in chrysocolla and pseudomalachite : Application to supergene copper mineralization. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20802, https://doi.org/10.5194/egusphere-egu2020-20802, 2020.

Phosphorus removal from wastewaters is a great interest to avoid eutrophication of natural waters (i.e. rivers, lakes). Additionally phosphorus recovery is also important due to increasingly limited nutrient resources. Struvite (MgNH₄PO₄*6H₂O) is of current interest as it is considered an alternative way for water remediation and potential use as a renewable fertilizer. Towards environmental sustainability, phosphorus and nitrogen removal and recovery from domestic, industrial, and/ or agricultural inputs, in the form of struvite may be an attractive alternative for the valorization of wastewaters (Mpountas et al., 2017).

Direct observations of crystal dissolution and growth process at the nano- level are possible through the use of Atomic Force Microscopy (AFM). A considerable number of studies have investigated mineral dissolution and growth by in-situ AFM imaging in a fluid-cell (Vavouraki et al., 2008; 2010). These direct observations and measurements allow the investigation of possible process mechanisms at the mineral-solution interface. Previous study on AFM imaging indicated struvite micro- to nanocrystal morphology. Hövelmann & Putnis (2016) investigated the interactions of ammonium-phosphate solutions with brucite (Mg(OH)₂) cleavage surfaces by AFM suggesting coupled brucite dissolution and struvite precipitation at the mineral-fluid interface. To the best of our knowledge, there are no records of nanoscale observations of dissolution and/ or growth of struvite surfaces. The aim of this study is to perform in situ AFM experiments using freshly cleaved struvite surfaces at flow conditions. Step retreat and/ or etch pit spreading were observed. Dissolution rates of struvite using doubly deionized water at different pH values were determined  whereas growth rates at different saturation values and pH using magnesium and ammonium-phosphate bearing solutions were also measured . Raman and SEM analyses were carried out to assess chemical structure and morphology of the obtained struvite crystals before and after AFM experiments.

Acknowledgments: The work has been supported by IKY-DAAD (2018-4) and KRHPIS II (Action PERAN).                                                                                

References: Hövelmann & Putnis, 2016. Env. Sci. Technol. 50, 13032−13041; Mpountas et al., 2017. J. Chem. Technol. Biotechnol. 92, 2075–2082; Vavouraki et al., 2008. Chem. Geol. 253, 243–251; Vavouraki et al., 2010. Cryst. Growth Des. 10, 60–69.

How to cite: Vavouraki, A., King, H., Putnis, C., and Koutsoukos, P.: In situ AFM imaging of dissolution and growth of struvite surface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21866, https://doi.org/10.5194/egusphere-egu2020-21866, 2020.

The marine Fe-Mn polymetallic nodules contain relatively high concentrations of Mn, Cu, Ni, Zn, Co and rare earth elements plus yttrium (REY), with a growing economic potential interest in their exploitation. To determinate the metallogenic processes and occurrence phases of the economic metals in the Fe-Mn nodules, we have undertaken high resolution mineralogical and geochemical studies of Fe-Mn nodules collected from the South China Sea (SCS).
The whole-rock mineralogical and chemical compositions of the SCS Fe-Mn nodules indicate hydrogenetic origin. The Mn mineral phases mainly are composed of nanocrystalline vernadite with interlayered 10 Å and 7 Å phyllomanganates, such as todorokite, birnessite, and buserite. Fe(-Ti) oxides/hydroxides are intergrown and essentially X-ray amorphous feroxyhyte and goethite. But we recognize two main types of internal microlayers in the SCS Fe-Mn nodules: Layer type A of suboxic diagenetic precipitates with extremely high Mn/Fe ratio and concentrations of Cu, Ni, Zn, Ba, Li and Mg; Layer type B of oxic hydrogenetic accretions with low fractionation of Mn and Fe and high contents of Co, REY, Ti, Sr and Pb. Furthermore, the elemental mapping indicates that the enrichment of Co and REY mainly associated with Fe mineral phases rather than Mn mineral phases, which are enriched in Mg, Cu, Ni, Zn, Li and Ba. Two mineralization processes and distributions of metals in the individual microlayers respectively are controlled and occurred by the different mineral phases. The increasing occurrence of 10 Å and 7 Å phyllomanganates present in the Layer type A are typically enriched in trace metals such as Ni, Cu, Zn, Li, Ba, and Mg, whereas the metals associated with the Layer type B include Co, Ti, Pb, Sr, REY, which might be carried by the intergrown of Fe(-Ti) oxyhydroxides and vernadite. Thus, hydrogenesis is more beneficial to the enrichment of Fe, Co, Ti, Sr, Pb and REY, while diagenesis is more favorable for the enrichment of Mn, Ni, Zn, Cu, Li, Ba and Mg during the metallogenic processes of the SCS nodules.

How to cite: Guan, Y.: Fine scale study of major and trace elements in the Fe-Mn nodules from the South China Sea and constraints on their formation processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21817, https://doi.org/10.5194/egusphere-egu2020-21817, 2020.

Kimberlites are the deepest melts that reach Earth’s surface and, therefore, can provide unique insights into the composition and evolution of the convective mantle through time. Application of isotope geochemistry to trace the composition of kimberlite sources has thus far been hindered by the ubiquitous alteration and incorporation of xenocrystic material in kimberlite rocks. Bulk-kimberlite analyses are typically considered reliable for Nd and Hf isotopes due to their overwhelmingly higher concentrations in kimberlite melts compared to common mantle and crustal contaminants. Conversely, Sr and Pb isotope compositions of bulk kimberlite samples are seldom considered representative of their parental melts thus requiring analysis of robust magmatic phases, primarily perovskite. Addressing the primary (i.e. magmatic) isotopic composition of volatile elements, such as N and noble gases, requires analyses of volatile-rich phases, and fluid inclusions in olivine represent a typical primary target in mantle-derived magmas. However, fluid inclusions in kimberlitic olivine are dominantly secondary in origin. Secondary inclusions can form at any time after crystallisation of their mineral host, which requires assessment of the origin of trapped fluids (i.e. pristine magmatic fluids, crustal fluids of external derivation, or combination thereof) before their isotopic composition can be used to make inferences about kimberlite mantle sources.

Here we present trace-element and Sr-Nd-Pb-He-N isotopic compositions of multiple olivine aliquots representing two different magmatic units of the ~88 Ma Wesselton kimberlite (Kimberley, South Africa). The Sr and Nd isotopic composition of olivine analysed by isotope-dilution (ID) TIMS are within the narrow range of perovskite ⁸⁷Sr/⁸⁶Sr (0.7043-0.7046) and whole-rock ¹⁴³Nd/¹⁴⁴Nd (eNd_i = 0.4–2.2) for the Kimberley kimberlites. These results indicate that the secondary fluid inclusions, which dominate the incompatible trace-element budget of olivine separates, have a pristine magmatic origin devoid of crustal contribution.

Helium isotope compositions were measured by laser heating of 1.6 to 9.8 mg of olivine using an ultrahigh-sensitivity compressor-source noble gas mass spectrometer. ³He/⁴He ratios are between 1.6 R_A and 3.7 R_A (where R_A indicates the atmospheric ³He/⁴He ratio), values more radiogenic than MORBs but comparable to HIMU OIBs. These results indicate a high time-integrated (U+Th)/He ratio in the source of the Kimberley kimberlites, which is consistent with the moderately high (i.e. HIMU-like) time-integrated U/Pb ratio implied by elevated initial ²⁰⁶Pb/²⁰⁴Pb in Wesselton olivine (19.1-19.5), Kimberley kimberlites (up to 19.9) and megacrysts in southern African Cretaceous kimberlites (up to 20.5). The combination of low ³He/⁴He, moderately radiogenic ⁸⁷Sr/⁸⁶Sr, and negative d³⁴S values (-2.6‰ to -5.7‰) require a contribution from subducted recycled material in the source of the Kimberley kimberlites. Conversely, a preliminary N isotope analysis of Wesselton olivine by in-vacuo crushing using a noble gas mass spectrometer returned a mantle-like d¹⁵N of -2.9‰, which might suggest limited recycling of surface N (d¹⁵N >0‰) in the source of these kimberlites. We conclude that the combination of Sr-Nd-Pb and He-N isotope tracing of fluid inclusions in olivine can provide a robust new approach to address the composition of kimberlite sources and, therefore, the evolution of the deep mantle through time.

How to cite: Giuliani, A., Koornneef, J. M., Barry, P., Will, P., Busemann, H., Maden, C., Maas, R., Greig, A., and Davies, G. R.: A preliminary assessment of the application of Sr, Nd, Pb, He and N isotope analysis to fluid inclusions in kimberlite olivine: A new approach to trace deep-mantle sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5267, https://doi.org/10.5194/egusphere-egu2020-5267, 2020.

The petrologic study of olivine-hosted melt inclusions (MIs) from alkaline primary Cenozoic basalts of Northern Victoria Land (Antarctica) provide new insights on the role of volatiles in the onset of rift-related magmatism. The concentration of volatile species (H₂O, CO₂, F, Cl) have been determined by Secondary Ion Mass Spectrometry (SIMS) on a selection of MIs which have been previously re-homogenized at high pressure and temperature conditions in order to avoid any heterogeneity and reducing the H diffusion. The least differentiated MIs vary in composition from basanitic to alkaline basalts, analogously to what is found in McMurdo volcanics, while their volatile concentrations reach up to 2.64 wt% H₂O, 3900 ppm CO₂, 1377 ppm F and 1336 Cl. Taking into account the most undegassed MIs a H₂O/(H₂O+CO₂) ratio equal to 0.88 was determined, which in turn brings the CO₂ content in the basanitic melt with the highest water content up to 8800 ppm.

Major and trace element melting modelling indicate that basanite and alkali basalt composition can be reproduced by 3 and 7% of partial melting of an amphibole-bearing spinel lherzolite respectively. Assuming a perfect incompatible behavior for H₂O and CO₂ these melting proportions allow to constrain the water and CO₂ contents in the mantle source in the range 780-840 and 264-273 ppm respectively. The resulting CO₂/Nb, CO₂/Ba and H₂O/Ce ratio are lower than those estimated for Depleted MORB Mantle (DMM), suggesting that the NVL Cenozoic alkaline magmatism could be originated by an enriched mantle source composed by a range from 70% to 60% of Enriched Mantle (EM) and from 30% to 40% of Depleted Morb Mantle (DMM).

A global comparison of fluid-related, highly incompatible and immobile/low incompatible elements such as Li, K, Cl, Ba, Nb, Dy and Yb allow to put forward that the prolonged (~500 to 100 Ma) Ross subduction event played a fundamental role in  providing the volatile budget into the lithospheric mantle before the onset of the Cenozoic continental rifting.

How to cite: Giacomoni, P. P., Ferlito, C., Bonadiman, C., Casetta, F., Ottolini, L., Zanetti, A., and Coltorti, M.: Geochemistry of basic magmatism of Western Antarctic Rift: implications for volatiles storage and recycling in the mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16794, https://doi.org/10.5194/egusphere-egu2020-16794, 2020.

Magnetoplumbite (yimengite-hawthorneite, HAWYIM), crichtonite (lindsleyite-mathiasite, LIMA) and hollandite (priderite) minerals are exotic titanate phases, which formed during metasomatism at the conditions of high alkali activity, especially K, in the fluids in the upper mantle peridotites. The paper presents data on experiments on formation of K-end-members priderite, yimengite and mathiasite, as the result of the interaction of chromite, chromite+rutile and chromite+ilmenite assemblages in the presence of a small amount of silicate material with H₂O-CO₂-K₂CO₃ fluids at 3.5 and 5 GPa and 1200°C. The experiments demonstrated the principal possibility of the formation of the titanates in the reactions of chromite with alkaline aqueous-carbonic fluids and melts. However, the formation of these phases does not proceed directly on chromite, but requires additional titanium source. The relationship between titanates is found to be a function of the activity of the potassium component in the fluid/melt. Priderite is an indicator of the highest potassium activity in the mineral-forming medium. Titanates in the run products are constantly associated with phlogopite. Experiments prove that the formation of titanates manifests the most advanced or repeated stages of metasomatism in mantle peridotites. Association of titanates with phlogopite characterizes a higher activity of the potassium component in the fluid/melt than the formation of phlogopite alone. The examples from natural associations, reviewed in the paper, well illustrate these conclusions. Experiments revealed the following features of crystallization of these phases and allowed interpretation of the titanate associations in metasomatized mantle peridotites.

(1) The principal possibility of the formation of minerals of crichtonite and magnetoplumbite groups and priderite in the reactions of chromite with alkaline aqueous-carbonic fluids and melts is confirmed. Such substances are considered as main agents of potassium metasomatism, leading to the formation of titanates in the upper mantle (Konzett et al., 2013; Rezvukhin et al., 2018).

(2) The formation of these phases does not proceed directly on chromite (e.g. Haggerty et al. 1983; Haggerty, 1983; Nixon, Condliffe, 1989), and requires additional titanium source. They are rutile and ilmenite, which are themselves usually are products of modal metasomatism of peridotites. This experimental fact demonstrates that the formation of titanates marks probably the most advanced or repeated stages of metasomatism in mantle peridotites.

(3) This is also proved by the relationships of titanates with phlogopite. Association of titanates with phlogopite characterized by a higher activity of the potassium component in the fluid/melt than the formation of phlogopite alone. Such conditions can again be created at the most advanced or repeated stages of mantle metasomatism.

(4) The relationship between titanates is also a function of the activity of the potassium component in the fluid/melt. Priderite is an indicator of the highest potassium activity in the mineral-forming medium. The above examples from natural associations (Zhou, 1986; Konzett et al., 2013; Almeida et al., 2014) well illustrate this conclusion.

How to cite: Vorobey, S., Butvina, V., and Safonov, O.: Syntheses of rare K-titanates (yimengite, mathiasite and priderite) at high TP conditions: application to modal mantle metasomatism., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-203, https://doi.org/10.5194/egusphere-egu2020-203, 2020.

Subducted metapelites are more prone to re-equilibrate during exhumation than mafic or ultramafic rocks to the point that recognizing high-pressure (HP) relicts is often very challenging. Geologic evidence from the Cima Lunga Unit (Central Alps) show this apparent discrepancy between high to ultra-high pressure metamorphism (28 kbar and 780 °C) recorded in mafic/ultramafic lenses, and Barrovian metamorphism (<10 kbar, 650°C) in the adjacent metapelitic rocks. We collected a white mica – garnet – biotite – plagioclase – kyanite (+ quartz, + zircon, + rutile) bearing metapelite adjacent to the garnet metaperidotite lens that displays an apparently well equilibrated Barrovian mineral assemblage (garnet + plagioclase + biotite), with no macroscopic or microtextural indication of a HP and/or HT metamorphic event (e.g. omphacite crystals; migmatitic texture; polyphase inclusions). Nevertheless, microstructures like atoll-like garnet or large white mica flakes surrounded by biotite and ilmenite replacing rutile suggest incomplete re-equilibration. We investigated garnet and phengite crystals by electron probe and laser ablation-ICP-MS mapping. Major and trace element mapping reveals very complex mineral zoning in both minerals. In particular, high Ti content in phengite and increasing P and Zr contents in pyrope-rich garnet indicate that the studied rock underwent a HP-HT event. This is also supported by Zr in rutile thermometry that indicates temperatures well above the Barrovian metamorphism (T > 700 °C). We combined detailed textural analysis with petrological-geochemical data and thermodynamic modelling to reconstruct the metamorphic evolution of the studied rock. We show that, thank to incomplete re-equilibration, the rock documents an evolution from prograde to UHP-HT peak (27 kbar and 800 °C) to retrograde (Barrovian) conditions (10 kbar and 620 °C). Noteworthy, peak metamorphic conditions of metapelite coincide with peak metamorphic conditions of the garnet metaperidotite. Lastly, geochemical evidence for minor wet melting of the studied metapelite at HP-HT conditions was recognized and is likely linked to the dehydration of chlorite to form garnet peridotite in the adjacent ultramafic body. We propose that metapelites and ultramafic rocks were coupled before subduction or at least in its early stage. This finding opens new scenarios for the geodynamic interpretation of the Cima Lunga unit. We propose that the ultramafic lenses at Cima di Gagnone were parts of the exhumed and serpentinised mantle emplaced at the hyper-extended European continental margin of the Piemont-Ligurian ocean. Slices of the margin were detached and tectonically mixed in the subduction channel. These new constraints call for re-evaluation of the paleogeographic position of the Adula-Cima Lunga nappe.

How to cite: Piccoli, F., Lanari, P., Hermann, J., and Pettke, T.: How to disclose local equilibrium in subducted metapelites from the Cima Lunga Unit (Central Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2674, https://doi.org/10.5194/egusphere-egu2020-2674, 2020.

Small portions of pristine melt with diameters of 2 to 50µm are increasingly recognized as a rather common occurrence in high grade metamorphic terranes which experienced melting. Their study delivers crucial chemical information on partial melts at depth. But they are also unique "natural experimental charges" where the behaviour of the silicate melt can be investigated, directly in the natural rocks, under P-T-t conditions which cannot be completely reproduced in the laboratory.

Each nanogranitoid case study has consistently shown H₂O-bearing, silica and alkali-rich melt. However, rather than a classic granitoid assemblage consisting mainly of quartz and feldspar(s), on cooling these isolated melt droplets produce a plethora of mineral phases identified via microRaman spectroscopy that are rarely –or never- observed as rock-forming minerals. Cristobalite (tetragonal) and tridymite (orthorhombic) are often present as SiO₂ polymorphs, and hexagonal kokchetavite as a polymorph of KAlSi₃O₈. NaAlSi₃O₈ occurs as orthorhombic kumdykolite, whereas CaAl₂Si₂O₈ may occur either as monoclinic svyatoslavite or trigonal dmisteinbergite. Two presently unidentified phases have been also recognized via Raman and analysed via electron microprobe. One has the main peak at 426-430 cm^-1 and has the composition of a granitic glass, whereas the second has a main peak at 412 cm^-1 and a variable composition depending on the inclusion in which it occurs. As their main peaks occur in the same region of most tectosilicates, it is likely that they are two new polymorphs of feldspar, to the best of our knowledge never reported before. These polymorphs have been so far identified in inclusions mainly hosted in garnet, zircon and, in one case, sapphirine and trapped under an extremely variable range of metamorphic conditions (from low P migmatites to UHP eclogites) in very different rock types (metagranitoids, metasediments, mafic and ultramafic rocks).

Microstructures confirm that all of these phases crystallize directly from the trapped melt on cooling, independently of the internal P of the inclusions or the original conditions of melt entrapment. They appear to be the result of metastability in the inclusions, possibly during rapid crystallization of a melt, not caused by rapid cooling but by the peculiar undercooled and supersaturated conditions achieved on cooling by a melt confined in a small cavity (Ferrero & Angel, 2018). According to this possibility, these polymorphs can be regarded as kinetically stabilized, yet possibly thermodynamically metastable, phases as recently proposed by Zolotarev et al. (2019) for dmisteinbergite. A preliminary crystallization experiment on a haplogranitic melt at undercooled conditions however failed to reproduce such phases. Another possibility is that under natural cooling the confined inclusions experience underpressurization, and the system (i.e. the trapped melt) reacts crystallizing phases, i.e. the polymorphs, less dense than their common counterparts. This would result in the decreasing of the P gradient between inclusions and surrounding rock, equivalent to reducing the free energy of the system.

References

Ferrero, S. & Angel, R. 2018. JPet 59, 1671–1700.

Zolotarev, A.A. et al. 2019. Minerals  9, 570.

How to cite: Ferrero, S., Angel, R. J., Borghini, A., Wannhoff, I., Fuchs, R., Tedeschi, M., Gianola, O., O'Brien, P. J., Wunder, B., and Ziemann, M. A.: Strange polymorphs and where to find them: a melt inclusion story , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9085, https://doi.org/10.5194/egusphere-egu2020-9085, 2020.

Over the recent years, Raman elastic barometry has been developed as an additional method to calculate metamorphic conditions in natural systems. A major advantage of Raman elastic barometry is that it does not depend on thermodynamic databases and classic geobarometry methods but relies on mechanical calculations. As a consequence, Raman elastic barometry offers an independent method for estimating the pressure conditions that prevailed at the time of entrapment of minerals during growth of their hosts.

The difference between the pressure calculated using elastic geobarometry and that calculated by phase equilibria methods has recently been employed to estimate the extent of metamorphic reaction overstepping in natural systems. Quantification of the latter however implicitly assumes that the rheology of the inclusion-host system is perfectly elastic. This assumption may not hold at high temperatures, where viscous creep of minerals takes place.

The amount of viscous relaxation of a host-inclusion system is a path-dependent quantity which mostly depends on the temperature-time (T-t) path followed. Here, we present examples of visco-elastic relaxation of mineral inclusions and calculate the apparent reaction overstepping which results by assuming that the mechanical system is purely elastic. Our modelling shows that host-inclusion systems that experienced large peak temperatures for long periods of time will retain inclusion residual pressures that cannot be simply related to the growth of their hosts and should therefore not be used for reaction overstepping calculations.

How to cite: Moulas, E., Zhong, X., and Tajcmanova, L.: Viscous relaxation of mineral Inclusions and its implications for reaction overstepping calculations in metamorphic rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7568, https://doi.org/10.5194/egusphere-egu2020-7568, 2020.

Trapped and sheltered inside other crystals, mineral inclusions preserve fundamental and otherwise lost information on the geological history of our planet. In the last decade, quartz inclusions in garnet have become a fundamental tool to estimate pressure and temperature of metamorphic rocks at the time of inclusion entrapment. In these approaches, as well as in all other applications, inclusions are regarded as immutable objects and the possibility of a change in their shape has never been considered.

With a detailed characterization of samples from greenschist and granulite facies, performed by optical and electron microscopy, EBSD, X-ray tomographic microscopy, laser Raman spectroscopy and FIB serial slicing, we show that after being trapped with irregular (“scalloped”) shape in low-temperature rocks, quartz inclusions in garnet from granulites formed at 750-900 °C and various pressures acquired a polyhedral “negative crystal” shape imposed by the host garnet, and almost exclusively defined by the facets of dodecahedron and icositetrahedron. A similar behaviour is also observed in biotite inclusions. The 3-fold and 4-fold morphological symmetry axes of the polyhedral negative crystals are parallel to corresponding crystallographic axes in the host garnet.

The systematic presence of a fluid film at the quartz-garnet boundary is not supported by Raman and FIB investigation.

Strengthened by microstructures indicating the process of “necking down” of polycrystalline quartz inclusions, our data support that - like in fluid inclusions changing shape to negative crystals - shape maturation of mineral inclusions occurs by temperature-assisted dissolution-precipitation via grain boundary diffusion. This process tends to minimize the surface free energy of the host-inclusion system by forming energetically favored facets and by decreasing the inclusion surface/volume and aspect ratios.

Optical investigation of numerous samples of worldwide provenance suggests that the negative crystal shape of quartz inclusions in garnet from granulites is a widespread microstructure that underpins a systematic phenomenon so far overlooked.

How to cite: Cesare, B., Parisatto, M., Mancini, L., Peruzzo, L., Franceschi, M., Tacchetto, T., Reddy, S. M., Spiess, R., and Marone Welford, F.: Quartz inclusions in garnet from high-temperature metamorphic rocks change their shape, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4143, https://doi.org/10.5194/egusphere-egu2020-4143, 2020.

With excellent outcrop, the eclogite-blueschist belt exposed in the Cycladic archipelago in the Aegean Sea, Greece, offers a spectacular natural laboratory in which to decipher the structural geology of a highly extended orogenic belt and to ascertain the history of the different fabrics and microstructures that can be observed. Using phengitic white mica we demonstrate a robust correlation of age with microstructure, once again dispelling the myth that ⁴⁰Ar/³⁹Ar geochronology using this mineral, produces cooling ages alone.

Further, we show that high-definition ultra-high-vacuum (UHV) ³⁹Ar diffusion experiments using phengitic white mica routinely allow the extraction of muscovite sub-spectra in the first 10-30% of ³⁹Ar gas release during ⁴⁰Ar/³⁹Ar geochronology. The muscovite sub-spectrum is distinct and separate to the main spectrum which is dominated by mixing of gas released from phengite as well as muscovite. The muscovite sub-spectra allow consistent estimates of the timing of the formation of microstructural shear bands in various mylonites, as well as allowing quantitative estimates of temperature variation with time during the cooling history of the eclogite-blueschist belt. Our new data reveals hitherto unsuspected variation in the timing of exhumation of individual slices of the eclogite-blueschist belt, caused by Eocene and Miocene detachment-related shear zones.

This study thus illustrates a new method for the quantitative determination of the timing of movement in mylonites and/or in strongly stretched metamorphic tectonites. Shear bands formed in such structures are rarely coarsely crystalline enough to allow mineral grains that can be individually dated using laser spot analysis. Where phengitic white mica is involved, interlaying is usually so fine as to preclude the application of laser methods. In any case, laser methods do not have the capability of extracting exact and detailed age-temperature spectra, and can never achieve the definition of the multitudinous steps of the age spectrum evident from our high-definition UHV diffusion experiments.

Previous work in the Cycladic eclogite-blueschist belt has incorrectly assumed that the diffusion parameters for phengitic white mica were the same as for muscovite. Arrhenius data suggest this is not the case, and that phengitic white mica is considerably more retentive of argon than muscovite. Previous workers have also erred in dismissing microstructural variation in age as an artefact, supposedly as the result of the incorporation of excess argon. This has led to inconsistencies in interpretation, because phengite is able to retain argon at temperatures that exceed those estimated using metamorphic mineral parageneses. In consequence, we discover a robust correlation between microstructure and age, even down to the detail present in complex tectonic sequence diagrams produced during fabric and microstructural analysis of individual thin-sections.

A critical factor is that the recognition of muscovite sub-spectra requires Arrhenius data in order to recognise the steps dominated by release of ³⁹Ar from muscovite. In turn this requires precise measurement of temperature during each heating step. To apply percentage-release formula for the estimation of diffusivity, there must be a sharp rise to the temperature in question, then that temperature must be maintained at a constant value, then dropped sharply to relatively low values.

How to cite: Forster, M., Nie, R., Yeung, S., and Lister, G.: Microstructural shear bands in mylonites dated using muscovite sub-spectra from high-definition ultra-high-vacuum (UHV) argon diffusion experiments with phengitic white mica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1813, https://doi.org/10.5194/egusphere-egu2020-1813, 2020.

Microstructures and the different thermoelastic properties of minerals ensure that no rock is ever under perfect hydrostatic stress at the grain level. If deviatoric stresses and strains significantly modify thermodynamic properties of minerals so that the equilibrium assemblage and compositions are different from that predicted from hydrostatic conditions, it is crucial to be able to measure the stress state of minerals in-situ in rocks. Forty years ago it was considered that ‘Analysis of residual stresses at the scale of mineral grains within a polycrystalline aggregate such as a rock is virtually intractable’ [1]. This is no longer true.

Confocal Raman spectroscopy allows spectra to be collected from small volumes of mineral grains within a section. The positions of Raman peaks depends on the elastic strains in the minerals through the phonon-mode Grüneisen tensors [2]. The development of precise DFT simulations of crystal structures and their Raman spectra now allows the components of the phonon-mode Grüneisen tensors to be calculated [3]. With these tensors it is possible to determine the strains from measured Raman peak positions, to thereby map the strain, and hence the stress state, of individual mineral grains. We have now extended the DFT simulations to show that the Raman shifts of crystals subject to symmetry-breaking stresses (e.g. around inclusions) are, as expected, not solely determined by the phonon-mode Grüneisen tensors of the ideal crystal. We have also recently developed the measurement of the change in peak intensities in cross-polarised Raman spectra to determine the stress [4] in these cases. For minerals such as garnets, this effect is stronger and therefore more sensitive to stress than the shifts in peak positions and offers at the moment the possibility to quickly visualise stress and strain fields in minerals in-situ in rocks. Quantitative stress values from this method await the determination of the piezo-phonon tensors for garnets, but comparison of peak positions and intensities show that the two methods return consistent results.

This work was supported by ERC-StG TRUE DEPTHS grant (number 714936) to M. Alvaro. N. Campomenosi was also supported by the University of Genova.

[1] Holzhausen & Johnson (1979) Tectonophysics 58, 237.

[2] Angel et al. (2019) Zeitschrift für Kristallographie, 234, 129.

[3] Murri et al. (2018) American Mineralogist, 103, 1869.

[4] Campomenosi et al. (2020) Contributions to Mineralogy and Petrology, accepted.

How to cite: Angel, R., Murri, M., Campomenosi, N., Mihailova, B., Prencipe, M., and Alvaro, M.: Measuring stress and strain in rocks by spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2869, https://doi.org/10.5194/egusphere-egu2020-2869, 2020.

Amphibole is one of the most abundant ’water’-bearing minerals in the Earth’s upper mantle. Amphiboles occur as interstitial grains, lamellae within pyroxenes or as daughter minerals within fluid inclusions.  Most commonly amphibole formation is related to mantle metasomatism, where the agent has a subducted slab (e.g. Manning 2004) or an asthenospheric origin (e.g. Berkesi et al. 2019).  After the formation of fluid inclusions, a subsolidus interaction can take place where the H₂O content of fluid inclusions may crystallize pargasite (e.g. Plank et al. 2016).

Here we present amphibole lamellae formation in mantle xenoliths from the Persani Mountains Volcanic Field that is interrelated to a reaction between fluid inclusions and host clinopyroxene.  Newly formed amphibole lamellae occur only in the surroundings of the fluid inclusions and grow within the host clinopyroxene in a preferred crystallographic direction.  Studied lamellae do not reach the rim of the host mineral implying that components needed for formation of amphibole lamellae in clinopyroxene could have only originated from the fluid inclusion itself.  We measured the major element composition of amphibole lamellae and host clinopyroxene (1) and used Raman spectroscopy and FIB-SEM on fluid inclusion study situated next to the lamellae (2).  Results support the hypothesis that chemical components (dominantly H⁺) migrated sub-solidus from the fluid inclusion into the host mineral after fluid entrapment via subsolidus interaction.  Beyond the clinopyroxene-hosted fluid inclusions, fluid inclusions in orthopyroxenes were also studied as a reference.  Our study shows that post-entrapment diffusion from a fluid inclusion into the host mineral changes the solid/fluid ratio of the mantle  which could modify the rheology of the lithospheric mantle.

Berkesi, M. et al. 2019. Chemical Geology, 508, 182-196.

Kovács et al. (2017) Acta Geodaetica et Geophysica, 52(2), 183-204.

Manning C. E. 2004. Earth and Planetary Science Letters, 223, 1-16.

Plank, T. A. et al. 2016. In AGU Fall Meeting Abstracts.

How to cite: Lange, T. P., Pálos, Z., Patkó, L., Berkesi, M., Liptai, N., Aradi, L. E., Szabó, Á., Szabó, C., and Kovács, I. J.: Amphibole lamellae formation in the upper mantle due to interaction of fluid inclusions and host minerals: a case study from Persani Mountains Volcanic Field, Transylvania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1192, https://doi.org/10.5194/egusphere-egu2020-1192, 2020.

Naturally, olivine reacts with CO₂-rich fluids, producing carbonates and silica. If in completion, this reaction will cause a large increase in the solid volume (~85%), which can generate a significant stress/force when it occurs in a confined space. This may be used to fracture the surrounding rocks in the context of the injection of industrially captured CO₂ into peridotites for permanent sequestration. Contrarily, this volume-increasing reaction may also clog transport paths and thus inhibit CO₂ access, leading to little or no volumetric increase at industrial time scales. Although observations from natural systems suggest that reaction-induced fracturing during peridotite carbonation can occur, the fracturing mechanism has not been experimentally reproduced under in-situ stress-temperature-chemical conditions. Here, we report 9 flow-through experiments performed on pre-compacted Åheim dunite (containing ~85% olivine) powders (grain size 36-50 µm) during carbonation reaction under controlled σ-P-T conditions. This was done using a purpose-built apparatus, consisting of a flow-through system accommodated with a uniaxial servo-controlled loading system. Before experiments, the dunite powders were compacted stepwise up to 250MPa to form a disc-shape sample with starting porosity of ~25%. The sample was covered by a thin Teflon sleeve plus Vaseline to reduce the friction against the vessel wall. The experiments were performed at a constant temperature of 150℃ and constant (Terzaghi) effective stress of 1, 5, 15MPa, respectively. The sample was first exposed to deionized (DI) water at a pore fluid pressure of 10MPa, and then the DI water was replaced, maintaining constant pore pressure of 10MPa, by flow-through of a certain chemical fluid, such as CO₂ saturated brine (containing 1M NaCl plus 0.64M NaHCO₃, pH~3), CO₂ saturated water (pH~3), NaHCO₃ saturated solution (pH~9) and NaHSO₄ solution (pH~3). The permeability was measured for all experiments using the flow-through system by means of the steady-state method, and each experiment took 2-4 weeks. The experiments show that the samples exhibited 0-0.37% compaction strain when CO₂ saturated brine, CO₂ saturated water, and NaHCO₃ saturated solution flow through, independently of poroelastic effects, and the sample permeability drops in the order from 10^-17 to 10^-20 m². By contrast, for the NaHSO₄ flow-through experiment where no carbonation reaction occurred, the sample permeability increased from 2*10^-17 to 7*10^-17 m², associated with 0.05% compaction. The sample mass after the NaHSO₄ flow-through experiment reduced ~5%, suggesting that magnesium and silica may be partly leached out from the sample. Microstructure observations and XRD analysis on these samples demonstrate a drastic reduction in porosity of the reaction zone where CO₂ was integrated into the crystal structure of the product carbonates by means of carbonation reactions. The mechanism responsible for the observed behavior seems to be that the dissolution of olivine that occurred first at the grain contact surface leads to compaction, followed by precipitation of carbonates at porous that clogs the transport paths and thus reduces the permeability, though the detailed chemical analysis is still performing. As a result, our current findings suggest that the volume-increasing precipitation produced via the carbonation reaction under in-situ subsurface conditions will clog transport paths.

How to cite: Liu, J., Wolterbeek, T., and Spiers, C.: Volumetric response of crushed dunite during carbonation reaction under controlled σ-P-T conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3047, https://doi.org/10.5194/egusphere-egu2020-3047, 2020.

In the eclogite facies shear zone of Bottarello, Monte Rosa, Western Alps [1], fault recrystallization around 600 °C gives concordant Lu-Hf (garnet) and ³⁹Ar-⁴⁰Ar (white mica, WM) 47 Ma ages whereas <100 m from the fault the unsheared rock at the same T preserves Mesozoic inheritance. The Ar retentivity of WM is not accurately predicted by hydrothermal laboratory experiments, because the latter are plagued by massive dissolution artefacts [2]. Independent field observations confirm that WM only starts losing Ar in dry rocks above 600 °C [3-8], but when retrograde reactions occur, WM can recrystallize and be totally reset below 230 °C [9]. The Bottarello fault obliterated all relict WM from the protolith; the neoformed WM records its own formation age.

The island of Naxos (Cyclades, Greece) is the classic example of multiple, coexisting WM generations [10]: relict pre-eclogitic basement WM, and eclogitic phengite retrograded to muscovite. Electron microprobe element maps demonstrate intergrowths at a scale <5 µm, which makes laser microprobe dating useless. Bulk mica dissolution for Rb-Sr gives Eocene ages [11], which agree with bulk K-Ar ages. This is paradoxical, as Ar diffusivity is c. 4 orders of magnitude higher than that of Sr [12]; the only explanation is that both chronometric systems record formation ages around 500-600 °C. The WM generations can be unravelled by their Ca/Cl/K signatures; coarse and fine sieve fractions are never isomineralic. Ages of pure mica generations are obtained by extrapolating Ca/Cl/K-vs-age trends.

The in-sequence thrusts of the Garhwal Himalaya add one complication: thrusting was long-lived. Microstructures combined with chemical microanalysis distinguish three monazite generations (dated by U-Pb) and three WM generations: relicts in microlithons, foliation-defining mica, and static coronas. As in the previous examples, intergrowths are <<10 µm and only combining Ca/Cl/K systematics with the observed differences in structural breakdown temperatures can assign the different WM ages in the same sample to chemically distinct generations [13]. WM formation ages overlap with Mnz ages and date the onset of faulting, the kinematic peak, and the post-faulting corona formation.

There is no free lunch: dating deformation is extremely labor-intensive and requires, always, establishing the context between microtextural, microchemical, petrological and multichronometric analyses. Whenever one of these four is missing, the tectonic reconstruction is invariably faulty [14].

[1] Villa &al, J Petrol 55 (2014) 803-830

[2] Villa, Geol Soc London Spec Pub 332 (2010) 1-15

[3] Di Vincenzo &al, J Petrol 45 (2004) 1013-1043

[4] Itaya &al, Island Arc 18 (2009) 293-305

[5] Heri &al, Geol Soc London Spec Pub 378 (2014) 69-78

[6] Laurent &al, Lithos, 272-273 (2017) 315-335

[7] Airaghi &al, J Metam Geol 36 (2018) 933-958

[8] Imayama &al, Geol Soc London Spec Pub 481 (2019) 147-173

[9] Maineri &al, Mineralium Deposita 38 (2003) 67-86

[10 Wijbrans & McDougall, Contrib Min Petr 93 (1986) 187-194

[11] Peillod &al, J Metam Geol 35 (2017) 805-830

[12] Cherniak & Watson, EPSL 113 (1992) 411-425

[13] Montemagni &al, Geol Soc London Spec Pub 481 (2019) 127-146

[14] Bosse & Villa, Gondwana Res 71 (2019) 76-90

How to cite: Villa, I. M.: Dating deformation: multichronometric examples from the Western Alps, Naxos, and the Garhwal Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4133, https://doi.org/10.5194/egusphere-egu2020-4133, 2020.

Bedding-parallel, fibrous calcite veins (commonly referred to as “beefs”) are widely developed within Eocene, lacustrine, laminated organic-rich source rocks in the Dongying Depression, Bohai Bay Basin, East China. Based on the study of vein petrography and fluid inclusions features, we demonstrate the vein was the product of hydrocarbon generation and expulsion from organic-rich shales. Consequently, the primary inclusions in the fibrous calcites recorded the fluid conditions during maturation of these source rocks. In most cases, the calcite-hosted primary inclusion assemblages are composed of the two-phase (oil + gas) hydrocarbon inclusions, with or without coexisting aqueous inclusions. Less commonly, the assemblages are made up of inclusions with only liquid hydrocarbon (i.e., monophase, high-density petroleum inclusions). In addition, many bitumen-bearing oil inclusions could also be observed in the fibrous calcite veins. By modelling the isochores of two-phase oil inclusions and coexisting aqueous inclusions, in light of the burial history for the basin, we conclude the fluid overpressure up to approximately twice (2x) the hydrostatic value (i.e., ~0.5–0.6x lithostatic) are the most common during the hydrocarbon generation and primary migration. The highest degrees of overpressure are recorded by the rare monophase petroleum inclusions. The resulting isochores of these highest density inclusions project to pressures that overlap with the lithostatic gradient. Thus, the monophase inclusions indicate pressures approaching and in some cases exceeding lithostatic. Our results indicate that fluids present during hydrocarbon generation and expulsion in organic-rich shales were indeed overpressured, but that lithostatic pressures were not the norm and evidently not a prerequisite for vein dilation, which means the fluid pressures during dilation of horizontal veins are not necessarily equal to the overburden throughout the history of the opening. This suggests that at least some of the vein dilation is accommodated and offset by concomitant narrowing of the adjacent wall rock laminae, likely by scavenging (dissolution/reprecipitation) of CaCO₃ from the adjacent wall rock, owing to the positive pressure dependence of calcite solubility, and presence of organic acids as byproducts of hydrocarbon generation.

How to cite: Wang, M., Chen, Y., and Steele-MacInnis, M.: Beef veins record fluid overpressure during oil primary migration in source rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5045, https://doi.org/10.5194/egusphere-egu2020-5045, 2020.

Thermal signatures as well as timing of fault motions can be constrained by thermochronological analyses of fault-zone rocks (e.g., Tagami, 2012, 2019).  Fault-zone materials suitable for such analyses are produced by tectocic and geochemical processes, such as (1) mechanical fragmentation of host rocks, grain-size reduction of fragments and recrystallization of grains to form mica and clay minerals, (2) secondary heating/melting of host rocks by frictional fault motions, and (3) mineral vein formation as a consequence of fluid advection associated with fault motions.  The geothermal structure of fault zones are primarily controlled by the following three factors: (a) regional geothermal structure around the fault zone that reflect background thermo-tectonic history of studied province, (b) frictional heating of wall rocks by fault motions and resultant heat transfer into surrounding rocks, and (c) thermal influences by hot fluid advection in and around the fault zone.  Geochronological/thermochronological methods widely applied in fault zones are K-Ar (⁴⁰Ar/³⁹Ar), fission-track (FT), and U-Th methods.  In addition, (U-Th)/He, OSL, TL and ESR methods are applied in some fault zones, in order to extract temporal information related to low temperature and/or recent fault activities.  Here I briefly review the thermal sensitivity of individual thermochronological systems, which basically controls the response of each method against faulting processes.  Then, the thermal sensitivity of FTs is highlighted, with a particular focus on the thermal processes characteristic to fault zones, i.e., flash and hydrothermal heating.  On these basis, representative examples as well as key issues, including sampling strategy, are presented to make thermochronological analysis of fault-zone materials, such as fault gouges, pseudotachylytes and mylonites, along with geological, geomorphological and seismological implications.  Finally, the thermochronological analyses of the Nojima fault are overviewed, as an example of multidisciplinary investigations of an active seismogenic fault system.

References:

1. Tagami, 2012. Thermochronological investigation of fault zones. Tectonophys., 538-540, 67-85, doi:10.1016/j.tecto.2012.01.032.
2. Tagami, 2019. Application of fission track thermochronology to analyze fault zone activity. Eds. M. G. Malusa, P. G. Fitzgerald, Fission track thermochronology and its application to geology, 393pp, 221-233, doi: 10.1007/978-3-319-89421-8_12.

How to cite: Tagami, T.: Low-temperature thermochronology of fault zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6060, https://doi.org/10.5194/egusphere-egu2020-6060, 2020.

Absolute dating of rock deformation is often hampered by the observation that the affected minerals are only partly re-equilibrated with respect to their isotopic composition.

Generally, three different processes enable mineral grains to adjust isotopically during the deformation event, i.e. volume diffusion, recrystallisation as well as dissolution and reprecipitation.

The degree to which the crystal structure is affected by these processes is different and thus the extent of isotopic equilibration during these processes generally differs in a way that diffusive element exchange is believed to be the most ineffective and slowest process, whereas re- and neo-crystallization seem to be fast and thorough.

Fluid-induced dissolution and reprecipitation is a very common mineral reaction mechanism in the solid Earth and as the crystal lattice is intensively reworked during this process, elemental and isotopic exchange between matrix and the newly formed crystal should be facilitated.   

Commonly, element and isotopic exchange during such mineral reactions is thought to occur via aqueous solutions, but new experimental as well as natural data show that the element transfer during mineral dissolution and reprecipitation can also occur in an amorphous material that forms directly by depolymerization of the crystal lattice.

Furthermore, precipitation of product minerals occurs directly by repolymerization of the amorphous material at the product surface, hence the entire element and isotopic transfer between reactant and product mineral might not involve equilibration with the intercrystalline transport medium with important consequences for the interpretation of age data from re- and neo-crystallized grains.

How to cite: Konrad-Schmolke, M. and Halama, R.: How trustworthy are absolute age data from reprecipitated mineral grains?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7963, https://doi.org/10.5194/egusphere-egu2020-7963, 2020.

Investigation of mantle xenoliths can provide information on the architecture and evolution of subcontinental lithospheric mantle through time. These reconstructions rely also on correct estimates of the pressures and temperatures (P-T) experienced by these rocks over time. Unlike chemical geothermobarometers, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on over-stepping of reaction boundaries and to identify other examples of non-equilibrium behaviour in rocks. Here we introduce a method that exploits the elastic anisotropy of minerals to determine the unique P and T of equilibration from a measurements of single-crystal mineral inclusions trapped in a crystalline host from an eclogite xenolith [1]. We apply it to perfectly preserved quartz inclusions in garnet from eclogite xenoliths in kimberlites. We show that the elastic strains of inclusions calculated from in-house Raman spectroscopy measurements of the inclusions are in perfect agreement with those determined from in-situ X-ray diffraction measurements performed both in-house and at the synchrotron. Calculations based on these measured strains demonstrate that quartz trapped in garnet can be preserved even when the rock passes into the stability field of coesite (high pressure and temperature polymorph of quartz). This supports a metamorphic origin for these xenoliths that provides constraints on mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that some key inclusion minerals do not always indicate the P and T attained during subduction and metamorphism.

This project has received funding from the European Research Council under the H2020 research and innovation programme (N. 714936 TRUE DEPTHS to M. Alvaro)

[1] M Alvaro, ML Mazzucchelli, RJ Angel, M Murri, N Campomenosi, M Scambelluri, F Nestola, A Korsakov, AA Tomilenko, F Marone, M Morana (2020) Fossil subduction recorded by quartz from the coesite stability field, Geology, 48, 24-28

How to cite: Alvaro, M., Mazzucchelli, M. L., Angel, R. J., Murri, M., Campomenosi, N., Scambelluri, M., Nestola, F., Korsakov, A., Tomilenko, A., Marone, F., Morana, M., and Alabarse, F.: Fossil Subduction Recorded By Quartz From The Coesite Stability Field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10711, https://doi.org/10.5194/egusphere-egu2020-10711, 2020.

The study of fluid inclusions (FI) composition (He, Ne, Ar, CO₂) integrated with the petrography and mineral chemistry of mantle xenoliths representative of the Sub Continental Lithospheric Mantle (SCLM) is a unique opportunity for constraining its geochemical features and evaluating the processes and the evolution that modified its original composition. An additional benefit of this type of studies is the possibility of better constraining the composition of fluids rising through the crust and used for volcanic or seismic monitoring.  

In this respect, the volcanic areas of Eifel and Siebengebirge in Germany represent a great opportunity to test this scientific approach for three main reasons. First, these volcanic centers developed in the core of the Central European Volcanic Province where it is debated whether the continental rift was triggered by a plume (Ritter, 2007 and references therein). Second, Eifel and Siebengebirge formed in Quaternary (0.5-0.01 Ma) and Tertiary (30-6 Ma), respectively, thus spanning a wide range of age. Third, Eifel is characterized by the presence of CO₂-dominated gas emissions and weak earthquakes that testify that local magmatic activity is nowadays dormant, but not ended (e.g., Bräuer et al., 2013). It is thus important to better constrain the noble gas signature expected in surface gases in case of magmatic unrest.

This work focuses on the petrological and geochemical study of mantle xenoliths sampled in the West Eifel and Siebengebirge volcanic areas (Germany) and aims at enlarging the knowledge of the local SCLM. Gautheron et al. (2005) carried out the first characterization of noble gases in FI of crystals analyzed by crushing technique (as in our study) but limited to olivines and to West Eifel eruptive centers. Here, we integrate that study by analyzing olivines, orthopyroxenes and clinopyroxenes from a new suite of samples and by including two eruptive centers from Siebengebirge volcanic field (Siebengebirge and Eulenberg quarries).

Xenoliths from the Siebengebirge localities are characterized by the highest Mg# for olivine, clinopyroxene and Cr# for spinel, together with the lowest Al₂O₃ contents for both pyroxenes, suggesting  that the mantle beneath Siebengebirge experienced high degree of melt extraction (up to 30%) while metasomatic/refertilization events were more efficient in the mantle beneath West Eifel.

In terms of CO₂ and noble gas concentration, clinopyroxene and most of the orthopyroxene show the highest gas content, while olivine are gas-poor. The ³He/⁴He varies between 5.5 and 6.9 Ra. These values are comparable to previous measurements in West Eifel, mostly within the range proposed for European SCLM (6.3±0.4 Ra), and slightly below that of MORB (Mid-Ocean Ridge Basalts; 8±1Ra). The Ne and Ar isotope ratios fall along a binary mixing trend between air and MORB-like mantle. He/Ar* in FI and Mg# and Al₂O₃ content in minerals confirm that the mantle beneath Siebengebirge experienced the highest degree of melting, while the metasomatic/refertilization events largely affected the Eifel area.

References

Bräuer, K., et al. 2013. Chem. Geol. 356, 193–208.

Gautheron, C., et al. 2005. Chem. Geol. 217, 97–112.

Ritter, J.R.R., 2007. In: Ritter, J.R.R., Christensen, U.R. (Eds.), Mantle Plumes: A Multidisciplinary Approach. Springer-Verlag, Berlin Heidelberg, pp. 379–404.

How to cite: Rizzo, A. L., Coltorti, M., Faccini, B., Casetta, F., Ntaflos, T., and Italiano, F.: Geochemistry of noble gas and CO2 in fluid inclusions from lithospheric mantle beneath Eifel and Siebengebirge (Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14005, https://doi.org/10.5194/egusphere-egu2020-14005, 2020.

We present various examples of age variations in Potassium-bearing minerals of tectonites obtained by ⁴⁰Ar/³⁹Ar in situ dating. Age variations in pre-kinematic clasts and syn-kinematic blasts both span large age ranges of significantly different ages values at the cores compared to the rims, calling for petrologic interpretation. Some of the synkinematic grains are overgrown by late- to post-kinematic blast that show consequently the youngest ages values within the samples. The concurrence of textural relation and age value in the case of late- to post-kinematic growth seem to be a robust tool to date the termination of deformation.  

Additional examples where break down reactions lead to dissolution of the prekinematic texture and crystallization of new minerals as coronas, within fractures of strain shadows also yield partly reset age values with larger scatter. The interpretation of those age values is more challenging and might be obscured by the 3D textural geometry of the analysed volume as well as disequilibrium between reactants and products.      

Commonly based on the percentage errors age values are interpreted as being geological significantly different, when errors do not overlap, or as natural geologic scatter, in the case errors overlap. This interpretation is biased by the absolute age value itself and might lead to over- and underestimations of geological events in geologic history. There is a strong need of error calculation that enables geological interpretation of tectonic event independent from their absolute age.

How to cite: Schneider, S.: Inter- and Intragranular age variations: Diffusion or mineral growth? – And what is wrong with the error? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21192, https://doi.org/10.5194/egusphere-egu2020-21192, 2020.

Ar/Ar-in-situ geochronology by laser ablation NGMS (noble gas mass spectrometry) provides a powerful tool to determine inter- and intra-granular age variations of potassium-bearing minerals while maintaining the structural integrity of a sample. This makes it an excellent method in targeting the understanding of the post-collisional evolution of an orogen by dating different mica generations. In order to investigate the timing of exhumation related to extensional deformation in the Internal Dinarides, we sampled paragneisses from the upper greenschist- to amphibolite-grade mylonitic detachment zones of two metamorphic core complexes (MCC’s). The MCC’s are located at the distal Adriatic passive margin (Cer MCC, central western Serbia) and within the Late Cretaceous suturing accretionary wedge complex (Motajica MCC, northern Bosnia and Herzegovina) that separates Adria-derived units from blocks of European affinity.

Mica grains were assigned to either pre-kinematic or syn-kinematic growth, according to their structural context, texture and grainsize. Pre-kinematic growth is characterized by large, deformed minerals of up to 3.5 mm in size, while rather fine-grained, recrystallized mineral aggregates that usually formed in the strain shadow of larger clasts represent syn-kinematic growth.

The ages of pre-kinematic white mica from paragneisses of the Motajica detachment range from approx. 80 to 25 Ma. They partly show a large intra-granular age spread characterized by significantly older core ages becoming progressively younger towards the rim. This pattern likely suggests diffusive loss of radiogenic Ar. Ages between 80-55 Ma in the central parts of the grains, associated with a top-W transport direction, are interpreted as the time interval of mineral growth and subsequent deformation in an accretionary wedge during E-ward subduction of the Adriatic passive margin underneath European units.

Syn-kinematic white mica from Motajica yielded ages between 22 and 16 Ma, which are interpreted as the time of peak activity of extension. This also corresponds with the time of crustal extension in the Pannonian Basin to the north. At Cer MCC, located roughly 150 km ENE of Motajica MCC and structurally below the accretionary wedge complex, ages of deformed white mica indicate exhumation between 19 and 15 Ma with a top-N directed transport.  

Our results suggest that the opening of the Pannonian Basin in response to slab-retreat underneath the Carpathian orogen resulted in the extensional reactivation of suturing thrusts that separated Adriatic from European units, leading to exhumation of parts of the accretionary wedge (Motajica MCC). This event was followed by the progressive exhumation of the passive Adriatic margin (Cer MCC) that occupied a structural position below the suturing accretionary wedge.

How to cite: Löwe, G., Schneider, S., Pfänder, J. A., and Ustaszewski, K.: Dating extensional deformation to unravel exhumation patterns in the Internal Dinarides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21425, https://doi.org/10.5194/egusphere-egu2020-21425, 2020.

Over the last few decades, monitoring of soil CO₂ efflux has been widely used in different scientific disciplines like volcanic and seismic hazard assessment, carbon capture and sequestration, geothermal well integrity, and others. We installed a comprehensive LICOR LI-8150 monitoring system on the Los Humeros normal fault, one of the major structures in the geothermal production field. Over a five-months period, seven accumulation chambers measured CO₂ efflux every hour in combination with an on-site meteorological station recording air temperature, air humidity, barometric pressure, precipitation, wind speed, and wind direction. Seismic activity was recorded simultaneously by a seismic array of 42 stations distributed across the volcanic complex, which identified both, high frequency, volcano tectonic (>10 Hz) and low frequency, long-period events (1-8 Hz). Furthermore, monthly geothermal production and re-injection data are available. Our study aims to (1) characterize significant temporal variations of soil CO₂ efflux, (2) assess the effect of environmental parameters, (3) analyze the possible influence of natural seismicity and geothermal exploitation (production/re-injection) on CO₂ degassing rates. The latter aspect plays an important role to better understand the hydraulic connection and communication between subsurface and surface along structural discontinuities in the volcanic-geothermal system.

How to cite: Jentsch, A., Düsing, W., and Jolie, E.: Continuous monitoring of fault-controlled CO2 degassing in the Los Humeros Volcanic Complex, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21937, https://doi.org/10.5194/egusphere-egu2020-21937, 2020.

The Ciomadul volcano is the youngest volcano (32 ka) built by the Neogene volcanism in the Carpathian-Pannonian Region. This volcanic area is characterized by intense gas emissions (Kis et al., 2017) (CO₂, CH₄, H₂S) in the form of bubbling pools, mofettes and mineral water springs. The isotopic compositions of carbon, ¹³C_CO2 up to -3‰ VPDB and helium up to 3.1 Ra suggest magmatic origin of the gas up to 80% (Kis et al., 2019).

Although the volcano seems to be inactive, several features, petrologic and geophysical studies suggest that melt-bearing magmatic body could still exist beneath the volcano (Harangi et al., 2015). Moreover the geodynamic system is characterized by frequent earthquakes with magnitude up to 7 at Vrancea area, close to the CO₂-rich gas emissions of Ciomadul and the neighbouring areas.

In 2015 we started the monitoring of the helium isotopic ratios of Ciomadul to chech the possible relationship with seismicity. Our results show that in several cases the helium isotopic ratios increase at a seismic event with magnitude between 4 and 5.8 suggesting a relationship between the two phenomena.

Harangi, Sz., Lukács, R., Schmitt, A.K., Dunkl, I., Molnár, K., Kiss, B., Seghedi, I., Á. Novothny, Molnár, M. 2015, Constraints on the timing of Quaternary volcanism and duration of magma residence at Ciomadul volcano, east-central Europe, from combined U-Th/He and U-Th zircon geochronology, Journal of Volcanology and Geothermal Research, 301, 66-80

Kis, B.M., Ionescu, A., Cardellini, C., Harangi, Sz., Baciu, C., Caracausi, A; Viveiros, F. 2017, Quantification of carbon dioxide emissions of Ciomadul, the youngest volcano of the Carpathian-Pannonian Region (Eastern-Central Europe, Romania), Journal of Volcanology and Geothermal Research, 341, 119–130

Kis, B.M., Caracausi, A., Palcsu, L., Baciu, C., Ionescu, A., Futó, I., Sciarra, A., Harangi, Sz. 2019, Noble gas and carbon isotope systematic at the seemingly inactive Ciomadul volcano (Eastern-Central Europe, Romania, Geochemistry, Geophysics, Geosystems, 20, 6, 3019–3043

This research belongs to the scientific project supported by the OTKA, K116528 (Hungarian National Research Fund), the EU and Hungary, co-financed by the European Regional Development Fund in the project GINOP-2.3.2-15-2016-00009 ‘ICER’ and the Deep Carbon Observatory.

How to cite: Kis, B.-M., Harangi, S., Palcsu, L., and Hegyeli, B.: Noble gas monitoring at the seemingly inactive Ciomadul volcano, Eastern Carpathians, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-869, https://doi.org/10.5194/egusphere-egu2020-869, 2020.

Tenerife (2034 km²), the largest island of the Canarian archipelago, is characterized by three volcanic rifts oriented NW-SE, NE-SW and N-S with a central volcanic complex, Las Cañadas Caldera, hosting Teide-Pico Viejo volcanoes. The North West volcanic Rift Zone (NWRZ, 72 km²) of Tenerife is one of the youngest and most active volcanic systems of the island, where two historical eruptions have occurred: Arenas Negras in 1706 and Chinyero in 1909. Diffuse degassing studies has become an important volcanic surveillance tool at those volcanic areas where visible manifestations of volcanic gases are absent, as in the case of NWRZ. Mapping soil gas emission along volcanic structures can provide a better understanding of the processes occurring at depth and allows monitoring the spatial distribution, magnitude and temporal evolution of the surface gas emissions. The geochemical properties of He, minimize the interaction of this noble gas on its movement toward the earth’s surface, and make this gas an almost ideal geochemical indicator of changes occurring in the magmatic plumbing system of the volcano (Padrón et al., 2013, Geology 41(5):539–542). Since 2014, surface He emission surveys have been performed once a year as an additional geochemical tool to monitor the volcanic activity of NWRZ. At 345 sampling sites soil gas samples were collected at 40 cm depth and analyzed for He concentration within 24 hours by means of QMS, model Pfeiffer Omnistar 422. The soil helium concentration data were used to estimate the diffusive helium flux at each point, to construct spatial distribution maps by sequential Gaussian simulation and then to estimate the total helium emission in the NWRZ. Helium emission ranged between non-detected values up to 7.2 mgm^-2d^-1, and the emission rate of the entire area was in the range ~1 – 45 kg d^-1. An increasing trend was observed in the period 2016-2018, showing a good temporal coincidence with a significant increase in seismic activity recorded in Tenerife. The promising results observed in the NWRZ and in other volcanic systems (Padrón et al., 2013) indicate that soil helium emission monitoring could be an excellent early warning geochemical precursory signal for future volcanic unrest.

How to cite: Recio, G., Dunn, E., McInally, Y., Pérez, N. M., Amonte, C., Alonso, M., Padrón, E., Asensio-Ramos, M., and Morales, F. A.: Diffuse He degassing monitoring of the Tenerife North-western Rift Zone (NWRZ) volcano, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11646, https://doi.org/10.5194/egusphere-egu2020-11646, 2020.

Some active volcanoes host thermal springs with ultra- (1<pH<2) and even hyper- (pH < 1) acidic waters with composition corresponding to a mixture of HCl and H2SO4 acids and with cations where Al and Fe are often the major components. Such springs sometimes are known as inferred drainages from active crater lakes (e.g., Rios Agrio at Poas and Copahue volcanoes). However, there are a number of acidic volcano-hydrothermal systems of Cl-SO4 composition at volcanoes without crater lakes.  At least ten groups of manifestation of this type are known for Kuril Islands. Several groups of acid volcanic springs including the famous Tamagawa springs are described in Japan.  Most of the acid Cl-SO4 volcano-hydrothermal systems are characteristic for island volcanoes, probably due to specific hydrological conditions of small volcanic islands. Maybe most known are coastal acid springs at Satsuma Iwojima volcano, Ryukyu arc, Japan. The accepted idea about the origin of such systems is scrubbing (dissolution) of magmatic HCl, HF and SO2 by groundwaters above magmatic conduits.  If so, the composition of acid springs must reflect the state of activity of a volcano. This review describes case histories that are known from the literature and from authors’ studies. Most of the volcanoes hosting acid systems show frequent phreatic activity. We show that  in contrast to crater lakes (Poas, Ruapehu, Copahue, White Island), acid springs on slopes of active volcanoes generally do not response on the preparing or ongoing volcanic eruptions. The aquifers and flow paths of the acid waters in volcanic edifices can be not associated with active conduits but with other degassing magmatic bodies and/or with deeper aquifers. One of the examples of such a complicated system is Ebeko volcano with Yuryevskye springs in Kuril Islands. These springs have a hydrochemical record since 1950s, and during this period Ebeko volcano had at least 10 strong phreatic eruptions.

How to cite: Taran, Y. and Kalacheva, E.: Ultra-acid volcanic waters: origin and response on volcanic activity. A review, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12242, https://doi.org/10.5194/egusphere-egu2020-12242, 2020.

Taal Volcano produces powerful eruptions and is the largest volcanic threat to the Phillipines. Six of the 24 known eruptions since 1572 have resulted in fatalities, and today several million people live with a 20-km radius. Since 2008, our volcano research group has conducted a collaborative research program with Phillipine scientists on applied geochemistry for volcano monitoring. One of the outcomes of this collaborative research was to observed precursor signals to the January 2020 eruptive activity.

Significant temporal variations in diffuse CO₂ emission at the Taal Crater Lake (TLC) was observed across the ~12 years. Two periods are especially noteworthy. From March 2010 to March 2011 the diffuse CO₂ emission rate increased from 763 ± 18  to 4.670 ± 159 tons per day. This anomalous increase coincided with the occurrence of a volcano-seismic unrest characterized mainly by a significant increase in the frequency of volcanic earthquakes, which was interpreted as indicating a new magma intrusion (Arpa et al., 2013; Hernández et al., 2017). A second anomalous diffuse CO₂ degassing at the TCL, from 860 ± 42 to 3.858 ± 584 tons per day during the period October 2016 to November 2017, was observed.

In addition to the geochemical surveys of diffuse CO₂ emission from the TCL, an automatic geochemical station for continuous monitoring of soil CO₂ efflux at the northern sector of the Taal Volcano Island crater rim was installed on January 2016. Although short-temp fluctuations in the diffuse CO₂ emission time series have been partially driven by meteorological parameters, the major CO₂ efflux changes were not driven by such external fluctuations. The major long-term variation of the CO₂ emission was an increase trend of the moving average of soil CO₂ efflux measurements (168 values) in 2017. Since 14 March, 2017, the station measured a sharp increase of CO₂ emission from ~0.1 up to 1.1 kg m^-2 d^-1 in 9 hours and continued to show a sustained increase in time up to 2.9 kg m^-2 d^-1 in November 2017. These combined geochemical and geophysical observations are most simply explained by magma recharge to the system, and represent precursor signals to the January 2020 eruptive activity.

Taal Volcano Background
Taal Volcano is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Located on the southwestern part of Luzon Island, Taal consists of a 15-22-km prehistoric caldera, occupied by the Taal Lake and the active vent complex of Taal Volcano Island with its Crater Lake (TCL).

Arpa M. C. et al (2013). Geochemical evidence of magma intrusion inferred from diffuse CO₂ emissions and fumarole plume chemistry: the 2010–2011 volcanic unrest at Taal Volcano, Philippines. Bulletin of Volcanology,  DOI: 10.1007/s00445-013-0747-9.

Hernández P. A. et al (2017). The acid crater lake of Taal Volcano, Philippines: hydrogeochemical and hydroacoustic data related to the 2010–11 volcanic unrest. Geological Society, London, Special Publications, 437, DOI:10.1144/SP437.17

How to cite: Pérez, N. M., Melián, G. V., Hernández, P. A., Padrón, E., Padilla, G. D., Baldago, Ma. C., Barrancos, J., Rodríguez, F., Asensio-Ramos, M., Alonso, M., Arcilla, C., Lagmay, A. M., Rodríguez-Pérez, C., Amonte, C., Pankhurst, M. J., Calvo, D., and Solidum, R. U.: Diffuse CO2 degassing precursors of the January 2020 eruption of Taal volcano, Philippines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19374, https://doi.org/10.5194/egusphere-egu2020-19374, 2020.

The southern margin of the Siberian craton, which experienced severe tectonic deformations in the Neoproterozoic-Cambrian and Jurassic, is currently a part of the Baikal seismic belt. In groundwater budget of the area, the main contribution is provided by the homogeneous South Baikal reservoir (SBR) with ²³⁴U/²³⁸U activity ratio (AR) 1.95–1.99 and U concentration 0.44–0.46 µg/L. Lateral penetration of the SBR water from the hydrostatically loaded deeper part of the lake (1000 m and more) to the adjacent Siberian craton area is promoted by gentle ruptures of the Angara thrust fault and sub-vertical shear fissures of the Main Sayan suture zone. In order to predict the time and place of a strong earthquake, AR are determined in groundwater from craton basement and sedimentary cover in an area from Lake Baikal to Irkutsk. AR values associated with deformational (Cherdyntsev–Chalov) effect vary from 1.0 to 3.5. Chemical impacts in evaporates result in AR values as high as 16. Data of a 7-year monitoring show key points in AR variations that might be used for prediction of a future strong earthquake.

This work is supported by the RSF grant 18-77-10027.

How to cite: Rasskazov, S., Chebykin, E., Ilyasova, A., and Chuvashova, I.: Hydro-isotopic (234U/238U) zoning of groundwaters in the seismically active southern margin of the Siberian craton, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12963, https://doi.org/10.5194/egusphere-egu2020-12963, 2020.

The 2017 M_W 5.5 Pohang earthquakes, which were known as triggered by enhanced geothermal system (EGS) stimulations, had significant effects on the groundwater system. This study aimed to identify the hydrogeochemical anomalies and to understand the response mechanisms of groundwater system to the earthquake. For this, the environmental isotopes (²²²Rn, Sr, ²H, and ¹⁸O), major ions, and time-series data (groundwater level, temperature, and electrical conductivity) were analyzed. Principal component analysis (PCA) was also employed. The results from time-series data showed the anomalies in the groundwater wells located near the epicenter. The hydrochemical parameters including stable isotopes data of ²H and ¹⁸O showed the different change patterns among groundwater wells before/after the earthquakes, which were related to the distance from epicenter, faults, and seawater. The environmental isotopes, radon and strontium, suggested the possible mechanisms underlying the effects of earthquakes by spatial distributions, such as seawater intrusion, water-rock interactions, shallow and deep aquifer mixing, deep fluid upwelling, and bedrock fracture opening. With this, the main cluster of PCA results was also distributed along these isotope concentration gradients.

Our findings proved the usefulness of environmental isotopes and hydrogeochemical parameters to understand the earthquake-related changes in groundwater system. These studied parameters and the adopted methods would be positively applied for other earthquake zones.

How to cite: Kim, J. and Lee, K.-K.: Hydrogeochemical anomalies associated with the 2017 MW 5.5 Pohang earthquake in South Korea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2786, https://doi.org/10.5194/egusphere-egu2020-2786, 2020.

The Dilatancy Diffusion model of Scholz et al (1973) is a model describing saturated rocks behaviour under differential tectonic stress in time domain, and one of the first trial of earthquake precursory phenomena listing and explanation. After around 50 years, improvements, outline and structure of this however successful model are still a reference point of many researcher. The role of water has been explained only as a pressure transducer, acting on host rocks, during the various stages of dilatancy diffusion, acting as a pressure cycle.

Theme of present model is the water active chemical role in DD.

A temperature pressure diagram of water aggregation state could be drawn as a section of the earth crust. Assuming that the brittle ductile transition line could be localised even close to 500 °C isotherm, most hypocentre are surely localised in liquid phase area, while some main shock localisation may fall even in water supercritical region.

I modelled the water isothermal behaviour in relation of most relevant variable acting on water in dilatancy diffusion: pressure. Pressure acting on water could drop drastically as soon as microcraks open. Then, water flow into newly created fractures, and, since tectonic load continues, pressure rise again, before main shock. In this pressure cycle, water chemical response, could be splitted into two diverse fields: liquid and supercritical, resulting however in a rock weakening.

• 1) Liquid. The entity of depressurisation makes the difference. According to Scholz et al (1973), and Brace et al (1966), the entity is high. It is a matter of water quantities and of volumetric geometry of microcracks. Ionic solubility depends slightly from pressure. Going into vapour phase is equal to a distillation process: when pressures rise again, this kind of water is extremely aggressive toward newly opened rock surfaces. If not, water could maintain most, not all, solute in. In every case, molecules like CO₂ and H₂ migrates away from water and, thanks to their characteristics (radius and electrostatic field), following the path of extremely little fissurations, normally secluded to water. Resulting water changes its chemical content.
• 2) Supercritical. Molecular structure of this aggregation state makes this fluid compressible. That is, its density varies highly with pressure. Solvent capability varies highly with density: supercritical water acquires polar solvent power with growing density. Solubility depends highly from pressure, with all consequences.

Subcritical crack growth. It is a common point of 1) and 2), and it could be a function of dissociation grade of water too. In an environment, with freshly created surfaces, quartz and silicates are subjected to a further weakening due to high dissociated water.

The integration of water chemistry in dilatation diffusion model is a needed upgrade and depict a situation in which, as soon as new crack creates, the chemical action of water can trigger a near irreversible process of rock weakening accelerating the main shock, since rock resistance could be lowered well below original breaking load.

How to cite: Calcara, M.: The Chemistry of Earthquakes: Chemical role of Water in Dilatancy Diffusion model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5482, https://doi.org/10.5194/egusphere-egu2020-5482, 2020.

Earthquakes are the main natural processes which are able to cause the strongest crustal perturbations in the world. Seismic events change crustal stress, both static and dynamic, in the co-seismic and post-seismic phases. In particular, hydrogeological and hydrogeochemical responses include: changes in water level, temperature, chemical composition, stream flow, and gas geochemistry. Among these parameters water level changes is the most recorded signal because of its fast acquisition and easy instrumentation. Depending on the involved mechanism, groundwater level variation is different. In particular, previous studies have highlighted permanent and transient signals which are characterized by step and spike changes both upward and/or downward. Only few studies have reported groundwater level variations induced by earthquakes that are very far away from the observation point and they are known as “teleseism”. In order to investigate relationship between groundwater properties and seismic cycle, since July 2014 we installed a multiparameter probe in a 100 m deep groundwater well (PF60.3) in Central Apennines (Central Italy). This monitoring well is part of a more complex monitored test site developed for this aim and it has recorded already hydrogeochemical anomalies related to Amatrice-Norcia 2016-2017 seismic sequence. The occurrence of the strongest earthquakes in the world (≈M_w>7.5), from the well probe installation (July 2014) until January 2020, has caused significant changes in groundwater level data. We analysed groundwater level behaviour in relationship to the occurrence of all 218 seismic events with M_w>6.5. We identified 16 interactions, where groundwater level is characterized by an anomalous spike change both upward and/or downward. In particular, we observed a significant interaction between signals for all the strongest seismic events with a M_w≥7.6, except for those happened in Papua Nuova Guinea and for those with ipocenter depth greater than 150 kilometers. We also found some interactions for less strong seismic events (6.5<M_w<7.5) but closer to the monitoring site. Among the observed correlations, 5 are characterized by a M_w between 8 and 8.2 meanwhile the others have a M_w between 6.5 and 7.9. The ipocenter depths of the considered 16 events are within 100 km, except two events that are deeper. We calculated the maximum amplitude of the perturbation and its duration. In this study we present our results with the main aim of expanding our understanding about perturbations due to distant earthquakes in the upper crust and in particular the relative fluid migration.

How to cite: Barberio, M. D., Gori, F., Barbieri, M., Billi, A., Franchini, S., Petitta, M., and Doglioni, C.: First observation of multi-groundwater level responses to the strongest worldwide seismicity in Central Apennines (Central Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5659, https://doi.org/10.5194/egusphere-egu2020-5659, 2020.

The Anninghe fault (ANHF) and the Zemuhe fault (ZMHF) with high level of seismic hazards in the China Seismic Experimental Site, located in southeastern of Tibet, are some of the most active faults in China. Measurement of the soil gas CO₂ has been conducted in three sites along the ANHF and the ZMHF for the first time. Totally, 394 sampling points along 15 profiles were measured. The fault locking degree of different segments of the ANHF and the ZMHF were inverted by the negative dislocation model using GPS velocity data  since 2013 to 2017. The measurements results show that the average and maximum value of CO₂ in the ZMHF is significantly higher than that in the ANHF. Soil gas CO₂ geochemistry yielded different spatial anomalous features, indicating the different properties and permeability of the faults. The inversion results reveal that the level of coupling including the locking depth and intensity along the southern segment of the ANHF was significantly larger than the northern segment of the ZMHF. Combining the CO₂ emission results, we concluded that the intensive locking of the segments reduced their permeability due to the self-sealing process, results in less gas to escape from the deep. Correspondingly, the creeping fault with low level of coupling can maintain high permeability which is more favorable to gas CO₂ migration.

How to cite: Li, Y., Yang, Y., and Chen, Z.: Soil gas CO2 emissions and fault locking along the Anninghe fault and the Zemuhe fault, in China Seismic Experimental Site, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7589, https://doi.org/10.5194/egusphere-egu2020-7589, 2020.

The aim of this study was to identify changes of trace element concentration in groundwater and test for coupling with seismic and volcanic activity in Iceland. Samples used in this study were collected between September 2010 and June 2018 from the HA-01 groundwater well in Hafralækur (Northern Iceland), south of the Tjörnes Fracture Zone (oblique transform zone), and near the Laxá and Skálfandafljót river valleys. The temperature of the groundwater from the HA-01 well is 71–76 °C, pH is ca. 10.2 (at ~ 25ºC), and the dissolved solid content is about 240 ppm, which is typical of low temperature geothermal groundwaters in inland areas of Iceland. The HA-01 well groundwater is also influenced by mixing between old ice age aquifer and younger aquifer groundwater. The same samples were previously analyzed for major element concentrations and isotopic ratios, with results - changes prior to seismic activity - being published in recent papers. The 495 earthquakes (Mw≥4.0, September 2010 to June 2018) considered in this study are from the USGS database. Twenty-two of these earthquakes occurred in the Tjörnes Fracture Zone with M_w between 4.1 and 5.5 whereas the remaining ones with M_w between 4 and 5.5 were related to the Bárðarbunga eruption in central Iceland, which began on 29 August 2014 and ended on 27 February 2015. Results of trace element analysis highlight characteristic variations in the temporal series related to the Bárðarbunga eruption (onset in August 2014) and to the 2018 seismic swarm that occurred in the Tjörnes Fracture Zone. In particular, a marked increase of Li, B, Ga, Mo and Rb and a slight increase of Sr and V were observed prior to and in connection with the onset of the Bárðarbunga eruption. Moreover, our results show a pre-seismic (2018 seismic swarm in the Tjörnes Fracture Zone) hydrogeochemical variability greater than the background variability. Despite the distance to the Bárðarbunga eruption site, GPS data from northern Iceland show a clear strain changes that are associated with the large dike intrusion that fed the eruption and are possibly correlated with the hydrogeochemical time series. Results from this study in Iceland show that the hydrogeochemical monitoring of volcanic and seismic areas is a promising method in the science of seismic and volcanic precursors.

How to cite: Franchini, S., Barberio, M. D., Barbieri, M., Billi, A., Boschetti, T., Jónsson, S., Petitta, M., Skelton, A., and Stockmann, G.: Hydrogeochemical changes in trace element concentrations in connection with earthquakes and a volcanic eruption in Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9403, https://doi.org/10.5194/egusphere-egu2020-9403, 2020.

The involvement of fluids in the earthquake cycle is a still open debate in the scientific community (e.g. Gratier et al., 2002). In the last years, new data from laboratory experiments and on-field discrete and continuous monitoring of soil gas, springs and gas vents were gathered worldwide (e.g. Martinelli, 2015; Nielsen et al., 2016). The aim of these studies was to better define the role of the observed fluid changes either as a trigger of earthquakes or as the co and post-seismic response to the transient (dynamic) and permanent (static) stress changes. This subject is particularly attractive in central and southern Apennines (Italy), where both huge water and CO₂ circulation at depth, occur (e.g Frondini et al., 2018). In this respect, the three long-lasting earthquake sequences that hit central Apennine in the last decades (1997, 2009 and 2016-2017, M_w up to 6.5) were accompanied by hydrological (increase or decrease in the spring discharges) and hydrochemical (variations in chemical composition, physico-chemical parameters) anomalies (e.g. Carro et al., 2005; Barberio et al., 2017; Petitta et al., 2018). Changes were observed mainly in the co and post-seismic phase and only a few pre-seismic signals were recorded. Temporal monitoring ranged from weeks to months, but higher sampling rates are needed to study crustal deformation processes (stress and volumetric strain) during the earthquake cycle. For example, since 2015 De Luca et al. (2016, 2018) are been performing high frequency (up to 20 samples/second) continuous monitoring of temperature, hydraulic pressure, and electrical conductivity in the Gran Sasso aquifer. They recorded unambiguous long-term (days to months) pre-Amatrice earthquake anomalies in both hydraulic pressure and electrical conductivity, related to its preparation stage.

In the light of the above, we decided to duplicate the equipment presently working in the Gran Sasso aquifer in a site with similar hydrological setting: the Venafro carbonate hydrostructure (Molise, Saroli et al., 2019). The site we chose is located in one of the most seismically active sectors of central-southern Apenninic belt, repeatedly hit in the past by large magnitude earthquakes and crossed by up to 20 km-long extensional fault systems (e.g. Galli & Naso, 2009). The main goals of our research are: i) measuring and understanding the dynamics of the carbonate aquifer, also through the analysis of rainfall, ii) deepening the relationships between aquifer behavior and earthquakes as well as to iii) widen the monitored areas.

Our experimental equipment includes a 3-channels 24-bit ADC set up for continuous local recording in groundwater (De Luca et al., 2016, 2018) in a horizontal borehole located in the drainage gallery “San Bartolomeo”, managed by Campania Aqueduct company. We started data acquisition in May 2019 by high-frequency continuous sampling (20 Hz for each channel) of physical parameters such as groundwater hydraulic pressure, temperature and electrical conductivity. We present some preliminary results (elaborated through a statistical approach) and possible explanations regarding the hydraulic pressure signals recorded before and during nearby (Mw 4.4, distance ~ 45 km) and regional (Albania, Mw 6.2, distance ~ 400 km) earthquakes, both occurred in November 2019.

How to cite: De Luca, G., Di Carlo, G., Frepoli, A., Moro, M., Pizzino, L., Saroli, M., Tallini, M., and Trionfera, B.: Continuous monitoring of physical parameters (temperature, electrical conductivity, water pressure) in a karst aquifer of central Italy (Venafro Mts., Molise): first results in a seismically active region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11644, https://doi.org/10.5194/egusphere-egu2020-11644, 2020.

Geochemical features of the geothermal and mineral waters from Apuseni Mountains, Romania

Alin-Marius Nicula¹, Artur Ionescu^1,2, Cristian-Ioan Pop¹, Carmen Roba¹, Walter D’Alessandro³, Ferenc Lazar Forray⁴, Iancu Oraseanu⁵, Calin Baciu¹

¹Babes-Bolyai University, Faculty of Environmental Science and Engineering, Str. Fantanele nr. 30, 400294, Cluj-Napoca, Romania (marius_alin92@yahoo.com)

²University of Perugia, Department of Physics and Geology, Via A. Pascoli 06123, Perugia, Italy

³Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo la Malfa, 153,

90146 Palermo, Italy

⁴Department of Geology, Babes-Bolyai University, Kogalniceanu 1, 400084 Cluj-Napoca, Romania

⁵Romanian Association of Hydrogeologists, Bucuresti, Romania

The Apuseni Mountains are located in the western part of Romania and separate the Pannonian Basin from the Transylvanian Basin. These mountains are famous and intensely studied for their important non-ferrous metal resources. Few data were published about the geothermal potential of this area. More works have been dedicated to mineral waters, while the geothermal waters are only briefly described, without sufficient emphasis on them. The current research is focusing on the two categories, cold mineral and geothermal water in the Apuseni Mountains, compared to the surrounding areas, in order to better understand their genesis and the general context of the geothermalism in the study region. A preliminary survey of these waters was done in 2019 taking water and gas samples from 41 sources.

The pH varies between 6.00 and 9.02 and, the lowest values have been measured in the CO₂-rich waters of the Southern Apuseni Mountains. Water temperatures vary between 11.1 ^â—‹C and 81 ^â—‹C. In the southern part of the Apuseni Mountains, the geothermal waters are of the calcium bicarbonate type (Ca-HCO₃), while in the north-western part, the sodium bicarbonate type (Na-HCO₃) is more common. The water sources from the north-western part are close to the Pannonian Basin and show features comparable to the thermal waters of this basin. Conductivity values show significant variations between 142 and 2040 µS/cm, but regional homogeneities were observed. The highest concentration of bicarbonate was measured in one of the localities of the northern study area (BeiuÅŸ Depression - 3318.4 mg/L). The dissolved heavy metal concentrations (Zn, Pb, Cd, Cr, Ni, Cu, Fe) in the water samples were also measured. For all the investigated waters, the heavy metal content was low. The highest concentrations were recorded for Fe 342.90 µg/L and Zn 86.14 µg/L. The isotopic data (δ¹⁸O and δ²H) demonstrate the meteoric origin of the thermal waters.

Some springs and wells release free gases. The gas chromatographic analyses show the prevalence of N₂ and CO₂, with minor amounts of CH₄ in the water sources close to the Pannonian Basin. The isotope composition of Helium shows values between 0.9 and 2.18 R/Ra indicating a prevailing crustal source with a significant mantle component. In the case of δ¹³C-CO₂ the values range between -12.7 and -6.1 ‰ vs.V-PDB, indicating that the CO₂ originates possibly from a limestone source.

How to cite: Nicula, A.-M., Ionescu, A., Pop, C.-I., Roba, C., D’Alessandro, W., Forray, F. L., Orașeanu, I., and Baciu, C.: Geochemical features of the geothermal and mineral waters from Apuseni Mountains, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-583, https://doi.org/10.5194/egusphere-egu2020-583, 2020.

In order to study groundwater anomaly related to the 2018 Hokkaido Eastern earthquake (Mw6.6) occurred on 6^th September, we have measured δD and δ¹⁸O values of commercial bottled mineral water at two sites in Iburi region, Hokkaido, Northern Japan from June 2015 to May 2019. At the Uenae site, 21km west of the epicenter, both δD and δ¹⁸O values are constant from June 2015 to February 2018. Then these values have decreased substantially from April 2018 to December 2018 with significant fluctuations. These variations may be attributable to a mixing of groundwater with light δD and δ¹⁸O values. At the Eniwa site 34km northwest of the epicenter, δD values have decreased slightly and monotonically, while δ¹⁸O values are constant from June 2016 to October 2018. Observed isotopic variations of the Uenae site are different from those found at the 2016 Tottori earthquake where the δ¹⁸O value of groundwater increased a couple of months before the seismic event, while the δD value was constant. These data were attributable to water-rock interaction in the aquifer. Thus, the mechanism of groundwater isotopic anomaly may be different between Tottori and Hokkaido earthquakes. In addition to the M6.7 earthquake, CO₂ injection by CCS project at Tomakomai, 13km southwest of the Uene site may be another factor to induce such variations. In order to evaluate the environmental impact of CO₂ injection, we should measure total carbonate concentration and δ¹³C value of carbonate at both sites. Then we will discuss mechanism of groundwater anomaly.

How to cite: Sano, Y., Kagoshima, T., Takahata, N., Shirai, K., Park, J.-O., Shibata, T., Yamamoto, J., Nishio, Y., Xu, S., Chen, A.-T., and Daniele, P.: Groundwater anomaly related to the 2018 Hokkaido Eastern Iburi earthquake in Northern Japan , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2287, https://doi.org/10.5194/egusphere-egu2020-2287, 2020.

The Duvalo locality is located in the SW of the Republic of North Macedonia, in the Ohrid region, near the village of Kosel. It is an area of strong soil degassing, called “volcano” by the local people despite volcanic activity has never been documented in the recent geologic history of the area [1]. A large area (thousands of sqm) shows signs of strong alteration and is devoid of vegetation. Until the 19^thcentury sulphur was mined from this area [1].

In August 2019, a campaign of soil CO₂ flux measurements and soil gas sampling was made. Duvalo is sometimes referred to as an active geothermal feature but no signs of enhanced geothermal gradient were found and the soil temperatures at 50 cm depth in this campaign were always within the range of local mean air temperatures. Soil CO₂ flux values ranged from 1.3 to 59,000 g/m²/d and can be modelled with the overlapping of 3 or 4 flux populations. A possible biological background is estimated in 6.8±1.8 g/m²/d while the other populations are characterized by an anomalous average flux ranging from 180 to 33,000 g/m²/d. The CO₂ total emission, estimated both with a statistical and geostatistical approach, provided similar values in the order of 50 t/d. This has to be considered as a minimum value because only areas with evident signs of alteration have been investigated. Nevertheless, the estimated output is quite high for an area unrelated with recent volcanism or geothermal activity.

The chemical composition of soil gases shows: CO₂ (96.6%), N₂ (1.8%), H₂S (0.6%) and CH₄ (0.3%) as the main gases. The present composition is almost indistinguishable from previous analyses made in 1957 and 1977 [1] pointing to a stability of the system in last decades. The isotope compositions indicate for CO₂ (δ¹³C -0.2 ‰) a pure carbonate rock origin, for CH₄ (δ¹³C -34.4 ‰ and δ²H -166 ‰) a thermogenic origin and for He (R/R_A 0.10) a pure crustal origin.

The H₂S released at Duvalo may be produced by either microbial or thermochemical sulphate reduction favoured by hydrocarbons whose presence can be inferred by the uprise of thermogenic methane. Partial oxidation of H₂S during its upflow, producing sulphuric acid, may be responsible of the production of abundant CO₂ through dissolution of carbonate rocks. Similar processes have been evidenced also in other parts of North Macedonia [2]. These gases rise up through the N–S trending normal faults bordering the seismically active Ohrid basin graben [3] being released to the atmosphere through the soils of Duvalo “volcano”.

This research was funded by: DCO Grant n. 10881-TDB “Improving the estimation of tectonic carbon flux”; GINOP-2.3.2-15-2016-00009 ‘ICER’ project and PO-FSE Sicilia 2014–2020 (CUP: G77B17000200009).

References

[1] Markovski B. et al., 2018. Duvalo a geological phenomenon near Ohrid. DOI: 10.18509/AGB.2020.05

[2] Temovski M., 2017. Hypogene Karst in Macedonia. In: Klimchouk et al. (eds.), Hypogene Karst Regions and Caves of the World, Springer

[3] Hoffmann N. et al., 2010. Biogeosciences, 7, 3377–3386

How to cite: Li Vigni, L., Ionescu, A., Molnár, K., Temovski, M., Palcsu, L., Cardellini, C., Gagliano, A. L., and D'Alessandro, W.: Duvalo (North Macedonia): A “volcano” without volcanic activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2449, https://doi.org/10.5194/egusphere-egu2020-2449, 2020.

The Ebeko volcano (50°41′N, 156°01′E) is located at the northern part of Paramushir Island and composed of several Quaternary volcanic cones. The Neogene volcano-clastic basement occurs below ~200 m asl. The post-glacial cone of Ebeko is composed by lava flows and pyroclastics of andesitic composition. The summit is represented by three craters (Northern, Middle and Southern). The modern phreatic and fumarolic activity of Ebeko started after a strong explosive phreatic–magmatic eruption from the Middle crater in 1934–1935 which ejected about 10⁶ t of andesitic ash and bombs. Last eruptive activity of Ebeko volcano began in October 2016 and continues to the present. 

Main feature of the hydrothermal activity of Ebeko is the existence of two thermal fields separated in the space. The summit field consists ~ 10 thermal grounds, low-temperature fumaroles (<120 °C) and near-boiling pools with no or weak outflowrates. The second thermal field, Yurievskie springs, is locatedat low elevations, ~550 m asl down to 280 m asl, on the western slope of Ebeko volcano in the canyon of Yurieva River. Gases from different parts of the summit thermal field are all water-rich (97–99 mol%) and show varying contents of HCl and total sulfur and ratios of C/S and H₂S/SO₂. All waters from the Yurievskie springs and Ebeko pools are ultra-acidic, with pH < 2. The Yurievskie waters are of the SO₄–Cl type (SO₄/Cl ratios are ~1:1molar and 3:1 by weight), whereas the SO₄/Cl ratio in Ebeko pools show low (<1) and varying SO₄/Cl ratios. Major and trace element composition of Ebeko-Yurievskie acidic waters is suggesting congruent dissolution of volcanic rocks. Oxygen and hydrogen isotopic composition of water and Cl concentration for Yurieva springs show an excellent positive correlation, indicating a mixing between meteoric water and magmatic vapor. In contrast, volcanic gas condensates of Ebeko fumaroles do not show a simple mixing trend but rather a complicated data suggesting evaporation of the acidic brine. Temperatures calculated from gas compositions and isotope data are similar, ranging from 150 to 250 °C, which is consistent with the presence of a liquid aquifer below the Ebeko fumarolic fields.

Thermal grounds and pools of the summit field are closely associated with the volcano activity. Each period of volcano excitation causes changes in the locations of major fumarole vents, crater lakes, and affects the chemical composition of water and gas. The Ebeko volcano eruption (from 2016 to the present) also triggered changes in the isotope and chemical composition of the Yuryevskie springs.

In this paper we report data on water and gas compositions of samples obtained during the 2016-2019 field seasons and compare partially published data from 2005-2014 field campaigns. This work was supported by the RFBR grant #20-05-00517.

How to cite: Kalacheva, E., Kotenko, T., and Voloshina, E.: Geochemistry of fluid manifistations of the Ebeko Volcano, Paramushir Island (Kurile Islands, Russia)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3395, https://doi.org/10.5194/egusphere-egu2020-3395, 2020.

La Palma Island is the north-westernmost and one of the youngest of the Canarian Archipelago. In the last 123ka, volcanic activity has taken place exclusively at Cumbre Vieja volcano which is located at the southern part of the island. Cumbre Vieja is characterized by a main north–south rift zone 20km long and 1950m in elevation covering an area of 220km² with volcanic vents located northwest and northeast. Cumbre Vieja is the most active basaltic volcano in the Canaries with 7 historical eruptions, being Teneguía (1971) the most recent one. The most relevant volcanic activity episodes occurred since Teneguía eruption, are two intense seismic swarms occurred beneath Cumbre Vieja on 7-9 and 13-14 of October 2017. Since visible volcanic gas emissions do not occur at the surface of Cumbre Vieja, the geochemical surveillance program has been focused mainly on diffuse degassing studies. In the last 18 years diffuse CO₂ emission surveys have been yearly performed in summer periods to minimize the influence of meteorological variations. Measurements have been performed following the accumulation chamber method in about 600 sites and spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse CO₂ emission. Herein we summarize the diffuse CO₂ emission time series during this period and describe the results obtained in the last 2019 survey. The soil CO₂ efflux values measured in 2019 survey ranged from non-detectable to 72.7gm⁻²d⁻¹. Diffuse CO₂ output was estimated in 1,064 ± 35td^-1, a value within the background +1s range (1,254 td^-1) (Padrón et al., 2015, Bull. Volcanol. 77:28). In the period 2001-2017, the diffuse CO₂ output released to the atmosphere from Cumbre Vieja volcano ranged between 320 to 1,544td^-1. Enhanced endogenous contributions of deep seated CO₂ might have been responsible for the higher CO₂ emission values measured in 2011 and 2013. After the October 2017 seismic swarms, diffuse CO₂ output showed an increasing trend from 788 to 3,251td^-1 in March 2018, to decrease gradually until 852td^-1 in September of that same year, and begin to gradually increase again to 2,371td^-1 in November 2018. These changes were possibly caused by an upward magma migration. Our results demonstrate that periodic surveys of diffuse CO₂ emission are extremely important for the detection of early warning signals of future volcanic unrest episodes at Cumbre Vieja.

How to cite: Di Nardo, D., Redfern, E.-M., Zummo, F., Martín-Lorenzo, A., Rodríguez-Pérez, C., Padrón, E., Melián, G. V., Sáez-Gabarrón, L., Alonso, M., Asensio-Ramos, M., Pérez, N. M., Hernández, P. A., Morales-González, F. A., and Pitti-Pimienta, L.: Geochemical monitoring of Cumbre Vieja volcano (Canary Islands) by summer diffuse CO2 degassing surveys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11386, https://doi.org/10.5194/egusphere-egu2020-11386, 2020.

Tenerife (2,034 km²) is the central and largest island of the Canarian archipelago, located about 100 km west of the African coast between 27º37’ and 29º25’N and between 13º20’ and 18º10’W. The structure of Tenerife is controlled by a volcano-tectonic rift-system with NW, NE and NS directions with Teide volcano located in the intersection of the three rifts. Teide is the highest stratovolcano in the Atlantic Ocean reaching 3,718 m.a.s.l. with its last eruption occurred in 1798 through an adventive cone of Teide-Pico Viejo volcanic complex. Persistent degassing activity, both visible and diffuse, takes place at the summit cone of the volcano, being the diffuse degassing the principle degassing mechanism of Teide (Mori et. al., 2001; Pérez et. al., 2013). As part of the volcanic monitoring program of INVOLCAN in Tenerife, 8 surveys were performed during summer 2019 in order to evaluate the short term variations of diffuse CO₂ and H₂S emissions in the summit crater. The emissions were calculated using data from 38 sampling sites homogeneously distributed inside the crater covering an area of 6,972 m² by means of a portable CO₂ and H₂S fluxmeter using the accumulation chamber method (Parkinson 1981). During the study period, CO₂ and H₂S emissions ranged from 33 ± 5 to 93 ± 25 t/d and from 0.6 ± 0.2 to 4 ± 0.1 kg/d, respectively. Despite the small changes observed in the temporal evolution, values are considered normal for a quiescence period in Teide volcanic system. Short term variations in CO₂ and H₂S emissions indicate changes in the activity of the system and can be useful to understand the behaviour of the volcanic system and as forecast of future volcanic activity.

References
Mori T. et al. (2001). Chemical Geology, 177, 85–99.
Parkinson K. J. (1981). Journal of Applied Ecology, 18, 221–228.
Pérez N. M. et al. (2013). Journal of the Geological Society, 170, 585–592.

How to cite: Alonso, M., Hoffman, H. T. A., Smith, J. G., Thompson, E., Rodríguez, F., Amonte, C., Asensio-Ramos, M., Pitti, L., Padrón, E., and Pérez, N. M.: Short-term variations of diffuse CO2 and H2S at the summit crater of Teide volcano, Tenerife, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11710, https://doi.org/10.5194/egusphere-egu2020-11710, 2020.