Castelli, Daniele

Connolly James Alexander Denis,

Ferrando, Simona

Frezzotti Maria Luce,

Groppo, Chiara

Maffeis, Andrea

English

Groppo, Chiara Teresa

Castelli, Daniele Carlo Cesare

Institutional Research Information System University of Turin

Book of Abstracts 3rd European Mineralogical Conference EMC 2020, Cracow, Poland ©Author(s) 2021      237  HP-UHP FLUID INCLUSION POST-ENTRAPMENT EVOLUTION PREDICTED BY MOLECULAR AND ELECTROLYTIC FLUID THERMODYNAMIC MODELS  Maffeis Andrea1, Ferrando Simona1, Connolly James Alexander Denis2, Groppo Chiara1, Castelli Daniele1, Frezzotti Maria Luce3   1Earth Science, University of Turin, Italy, 2Earth Science, ETH Zurich, Switzerland, 3Environment and Earth Sciences, University of Milan-Bicocca, Italy   A reliable characterization of the fluids released from a subducting plate is of primary importance to understand the processes that regulate the long-term chemical cycles. Ultrahigh-pressure (UHP) fluids are composed of solvent COHNS molecular volatiles and by solute non-volatile elements bounded to inorganic and organic species. Both direct (fluid inclusion, FI) and indirect (thermodynamic modeling, TM) approaches to study UHP fluids have reliability issues: i) post-trapping processes can affect the chemical composition of the FI, ii) the relatively few applications make the electrolytic-fluid TM still a poorly tested method to reconstruct subduction fluid compositions. In this work, we evaluated compositional data from primary FI trapped within UHP diopside from a chemically simple (CMFS-COHS) marble showing evidence for multiple events of mineral dissolution-precipitation (Brossasco-Isasca Unit, Dora-Maira Massif, Italian Western Alps). These FI are tri-phase multisolid aqueous inclusions (5-25 µm in diameter) consisting of H2OLiq (with traces of dissolved chlorides) + different kinds of solids (Cc/Mg-Cc ± Tlc ± Dol ± Serp ± Tr ± Py ± Gr) + bubble (H 2OV ± N 2 ± CH 4). Classical molecular-fluid TM allowed to model post-trapping reactions between FI and host diopside (i.e., discrimination among daughter, step-daughter, and incidentally trapped minerals). Electrolytic-fluid TM allowed modeling the chemical composition of the peak solute-bearing aqueous fluid (H2O: 88.5 wt%; solutes: 11.34 wt%; CO2 + H2S + CH4: 0.17 wt%) generated by progressive rock dissolution. The comparison between the modeled fluid composition with that reconstructed from FI allows to recognize the kind and extent of post-trapping chemical re-equilibration that occurred within UHP FI. Applying this multidisciplinary approach, we demonstrate i) that the most impacting post-trapping process in UHP FI is the H2O loss, with consequent preservation of the geochemical information in those FI lacking relevant post-trapping host-diopside chemical contamination; ii) that the electrolytic-fluid TM is highly supportive of the classical FI study to retrieve geochemical information on deep subduction fluids. 

HP-UHP FLUID INCLUSION POST-ENTRAPMENT EVOLUTION PREDICTED BY MOLECULAR AND ELECTROLYTIC FLUID THERMODYNAMIC MODELS

https://iris.unito.it/bitstream/2318/1805974/1/Maffeis_et_al_2021_EMC2021.pdf

HP-UHP FLUID INCLUSION POST-ENTRAPMENT EVOLUTION PREDICTED BY MOLECULAR AND ELECTROLYTIC FLUID THERMODYNAMIC MODELS

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