"Field and microstructural investigation of exhumed normal faults in quartzites and calc-schists (Schistes lustres, Alpine Corsica, France)."

At present, the investigation of the complex physical and chemical processes occurring during earthquake nucleation, propagation and arrest cannot be accomplished only by means of seismological investigations, mainly because of source, path and attenuation effects that result in loss of information transported by seismic waves. Here the need for a complementary approach which involves field geology (e.g., investigation of ancient now exhumed seismogenic structures), deep drilling projects (e.g., investigation of active seismogenic structures), microstructural (e.g., investigation of natural fault rocks) and laboratory (e.g., experiments reproducing seismic deformation conditions) studies. In this study, we propose that, because of the eastward migration of the lithospheric extension starting from the Oligocene, the normal faults now outcropping in Alpine Corsica are the exhumed analogs of the seismogenic structures now active at depth in the Italian Apennines. The investigated fault zone cut serpentinites, quarzites, marbles and calc-schists of the Schistes Lustrés Complex (Late Cretaceous- Early Oligocene). Microstructural (EDS equipped field emission scanning electron, optical microscope cathodoluminescence) and mineralogical (micro-Raman spectroscopy and X-Ray powder diffraction) studies conducted on rocks sampled from the normal faults, evidenced a sequence of seismic and inter-seismic deformation processes during exhumation: pseudotachylyte (scars of ancient seismic ruptures) produced at 8-15 km depth are overprinted by carbonate-rich veins and eventually cut by semi-amorphous silica- (including nano-particles of quartz) and carbonaceous-rich (possible remnants of graphitization processes of calcitic marbles and calce-schists under anoxic conditions) mirror-like fault surfaces. The above overprinting microstructural relationships suggests continuous seismicity aided by the ingression of pressurized CO2-rich fluids during exhumation. These relationships are consistent with those proposed between crustal-mantle degassing and CO2 fault fluid ingression that characterize the actual seismicity in the Italian Apennines.