Microtectonics of low-P low-T carbonate fault rocks

With the aim of deducing some general microtectonic processes responsible for the development of carbonate fault cores rock samples were collected in ten of such structures which are different in size attitude kinematics displacement and tectonic environment Samples were thin-sectioned and analysed under an optical microscope Microscopic evidence (i e at the scale of tens-to-hundreds of microns) shows that grain size reduction occurred mostly by cataclasis and occasionally by pressure solution Cataclasis involved three main processes here named intragranular extension fracturing chipping and shear fracturing lntragranular extension fracturing is more common in the early stages of cataclasis and produces a coarse breccia consisting of angular grains In a few cases pre-existing weaknesses and flaws control the fracture pattern associated with intragranular extension fracturing Chipping is more common in the advanced stages of cataclasis and produces a gouge consisting of a few survivor rounded grams within a fine matrix Shear fracturing seems less frequent than the other two processes and usually occurs in the advanced stages of cataclasis By considering the microscopic and mesoscopic evidence and the dissimilar frequency of dissolution structures in the analysed fault cores and damage zones It is Inferred that the studied fault zones probably acted as conduit-barrier permeability systems.