Deformation of high-pressure metamorphic rocks: mutual constraints from 2D cm-scale thermo-mechanical models and petrological observations
Résumé
How rocks deform at depth during lithospheric convergence and what are the magnitude of stress levels they
experience during burial/exhumation processes constitute fundamental questions for refining our vision of
short-term (i.e. seismicity) and long-term tectonic processes in the Earth’s lithosphere.
We here present a set of 2D numerical experiments of eclogitic rock deformation performed at cm-scale. The deformed
medium is composed of two mineral phases: omphacite and garnet. We carried out a series of experiments
for different background strain-rates and for a range of realistic pressure and temperature conditions. Results show
that fracturing of the entire eclogite rock can occur under HP-LT conditions for strain-rates even smaller than
those generally expected for seismic events.We also explore the ranges of parameters where garnet and omphacite
are deforming with a different deformation style (i.e. frictional vs. viscous) and discuss our modelling results at
the light of naturally deformed eclogitic samples. Finally, we show that in cases of fracturing, the first event of
frictional strain localisation constitutes a precursor for ductile strain localisation and results from the conversion
of the mechanical energy into heat (i.e. shear-heating).