Our strategy
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Development of a new generation of Thermo-Mechanical-Hydro-Chemical models to test the mechanical effects of metamorphic reactions due to volume changes, rheological changes and latent heat.
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Validation against laboratory experiments at determined P, T and strain rate conditions monitored during the reaction.
FIRST GOAL
Developing a new generation of Thermo-Mechanical-Hydro-Chemical (TMHC) models
The majority of current numerical models do not consider metamorphic transformation processes
Two reactions studied
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Quartz-coesite: a representative reaction for the continental crust, in which hydro-chemical components are not involved
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Serpentinization of peridotite: a key reaction in Earth Science, that involves huge ∆V and ∆H changes as well as fluid flow and compositional changes
There is a blatant methodological block ahead of us in this prospect because of the intrinsic difficulties in running non-constant volume TMHC models
TM models applied to quartz-coesite case study will be very complementary to the TMHC models (as the one we will develop for the serpentinization reaction), as they will provide ideal “benchmarks” to test TMHC models on a simple end-member case.
Some questions to answer
What controls the mechanical instabilities such as self-propagating transformation bands
What controls the growth of stable compacting “anticrack” veins vs. unstable shear bands
What is the effect of the ratio between strain rate and transformation kinetics
SECOND GOAL
Laboratory experiments to validate the model(s)
The appearance of coesite in quartz samples results in a seismic wave velocity increase that will be detected with our setup and used to track the reaction extent of the transformation in situ!
The final degree of transformation and its distribution throughout the sample will also be accurately retrieved from SEM images and EBSD mapping. Experimental results will then be compared to estimations based of evolution of wave speeds and results from thermo-mechanical models. In addition, potential brittle unstable faulting will be identified via the recording of acoustic emissions (AEs) !
Serpentinization under stress has never been realized on synthetic (i.e. chemically controlled) materials in the laboratory, and especially at P-T conditions relevant for subduction zones environments ! Preliminary experiments on serpentinite dehydration in the Griggs apparatus have yet emphasized that reaction evolution (kinetics, microstructures of the porosity) can perfectly be monitored with passive and active acoustic monitoring, which is a novel tool for studying such reactions.
Many data to extract and analyse
Stress-strain
curves
Phase identification and quantification using SEM and EBSD
Active acoustic tracking to follow reaction progress
Post-mortem micro-structures
Passive acoustic monitoring to track for a change of deformation mode (from ductile to brittle)
Raman (or FTIR) spectroscopy, or nanoSIMS to estimate water content in the samples/grains
