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Reorganization of carbonaceous materials during geological burial and deformation : Experiments and natural examples

Benjamin Moris-Muttoni 1, 2 
2 Géodynamique - UMR7327
BRGM - Bureau de Recherches Géologiques et Minières (BRGM), ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327 : UMR7327, INSU - CNRS - Institut national des sciences de l'Univers, UO - Université d'Orléans : UMR7327
Abstract : Particles of carbonaceous material (CM), present in most sediments, experience a progressive evolution during their burial from immature and amorphous structure to fully mature and crystalline graphite. This transformation, decomposed in two successive stages (carbonization then graphitization), can be quantitatively followed with Raman spectroscopy (RSCM), and is assumed to be controlled at the first order by temperature, while the potential role of other parameters is still controversial. In this work we explore the effect of strain on CM crystallinity with natural examples from accretionary complexes (Shimanto belt, Kodiak Accretionary Complex, Alps) and experiments encompassing both high strain rate (seismic) and low strain-rate (non-seismic) deformation. We focused on the low temperature range from 200 to 350°C, spanning the carbonization and the early graphitization stages. We used high-resolution profiles to correlate RSCM signal to microstructures. Intensity ratio (IR) appears to be the most relevant RSCM parameter to record deformation. Irrespective of the deformation mechanism (i.e. in low and high strain-rate examples), IR is increased in the zone where strain is localized, demonstrating the large influence of strain on Raman signal. In addition, using geological examples of contact metamorphism, combined with flash heating experiments, we demonstrated the potential of a RSCM feature (D3/Gsl Ratio) to detect short-lived and intense heating events. When applied to Black Fault Rocks considered as the result of quenching of a melt formed during fast seismic slip, these new tools (profiles of IR and D3/Gsl Ratio) can discriminate fault cores that melted from those where only mechanical comminution was active.
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Benjamin Moris-Muttoni. Reorganization of carbonaceous materials during geological burial and deformation : Experiments and natural examples. Tectonics. Université d'Orléans, 2021. English. ⟨NNT : 2021ORLE3154⟩. ⟨tel-03714417⟩

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