3:30 PM - 3:45 PM
[SCG45-31] Deciphering deformation processes using Raman spectroscopy on carbonaceous material: the insights from slow strain-rate experiments
★Invited Papers
Keywords:carbonaceous material, fault zones, deformation experiments, Raman spectroscopy
Due to the widespread presence of carbonaceous material (CM) in the sediments that constitute accretionary prisms or paleo-subduction zones, Raman spectroscopy on carbonaceous material (RSCM) has recently developed as a very efficient and versatile geothermometer. The method is based on the progressive and irreversible evolution of CM from an immature, disorganized state towards a fully organized, graphite structure, under the application of an increasing temperature.
If the effect of heating on CM crystallinity is well documented, questions remain as to the effect of other parameters, such as strain. This issue is particularly acute in fault zones, where potentially high amount of strain and localized heating may coexist and influence CM crystallinity. While several studies have described anomalous Raman signature of CM in the core of fault zones, one can wonder whether these anomalies originate from short-lived pulses of heating during seismic slip, or from long-lasting, slow strain-rate slip without local temperature rise.
To answer these questions, we have carried out in this work series of slow strain-rate deformation experiments on CM-bearing sediments, both in Paterson-type and Griggs-type apparatuses, under variable conditions of temperature (400 to 700°C), pressure (150MPa to 1GPa) and strain-rates (10-4 to 10-7s-1). Paterson-type experiments showed stick-slips episodes of slip, while in Griggs-type experiments only continuous deformation occurred. From the observation of the microstructures in the samples after the experiments, it appeared that strain is systematically heterogeneously distributed. High-strain domains, where grain-size is strongly reduced, consist in many instances (even in high-pressure experiments where no stick-slip were observed) in the juxtaposition of micro-breccia (rounded clasts, high porosity) and ductile layers (elongated clasts, low porosity).
RSCM analyses of experimentally-deformed material showed that CM crystallinity is enhanced in high-strain zones, irrespective of the microstructures and deformation process. In particular, such an increase is observed in experiments where no stick-slip event was observed and in high-strain ductile layers where no evidence for brittle deformation is present. The enhanced crystallinity observed in this set of experiments is therefore best explained as the result of strain localization.
These deformation experiments confirm independently the effect of strain on CM evolution, which we demonstrated in a separate work on natural fault zones. Altogether, these studies highlight the complexity of the processes that govern the crystallinity of carbonaceous particles, which include both temperature and strain, amongst other possible parameters. Therefore, CM signature in fault zones could potentially lead to discriminate creeping fault zones from the ones that rupture seismically and liberate by friction a large amount of heat.
If the effect of heating on CM crystallinity is well documented, questions remain as to the effect of other parameters, such as strain. This issue is particularly acute in fault zones, where potentially high amount of strain and localized heating may coexist and influence CM crystallinity. While several studies have described anomalous Raman signature of CM in the core of fault zones, one can wonder whether these anomalies originate from short-lived pulses of heating during seismic slip, or from long-lasting, slow strain-rate slip without local temperature rise.
To answer these questions, we have carried out in this work series of slow strain-rate deformation experiments on CM-bearing sediments, both in Paterson-type and Griggs-type apparatuses, under variable conditions of temperature (400 to 700°C), pressure (150MPa to 1GPa) and strain-rates (10-4 to 10-7s-1). Paterson-type experiments showed stick-slips episodes of slip, while in Griggs-type experiments only continuous deformation occurred. From the observation of the microstructures in the samples after the experiments, it appeared that strain is systematically heterogeneously distributed. High-strain domains, where grain-size is strongly reduced, consist in many instances (even in high-pressure experiments where no stick-slip were observed) in the juxtaposition of micro-breccia (rounded clasts, high porosity) and ductile layers (elongated clasts, low porosity).
RSCM analyses of experimentally-deformed material showed that CM crystallinity is enhanced in high-strain zones, irrespective of the microstructures and deformation process. In particular, such an increase is observed in experiments where no stick-slip event was observed and in high-strain ductile layers where no evidence for brittle deformation is present. The enhanced crystallinity observed in this set of experiments is therefore best explained as the result of strain localization.
These deformation experiments confirm independently the effect of strain on CM evolution, which we demonstrated in a separate work on natural fault zones. Altogether, these studies highlight the complexity of the processes that govern the crystallinity of carbonaceous particles, which include both temperature and strain, amongst other possible parameters. Therefore, CM signature in fault zones could potentially lead to discriminate creeping fault zones from the ones that rupture seismically and liberate by friction a large amount of heat.