Evoluzione microstrutturale con il rigetto in faglie sismogenetiche in tonalite (faglia delle Gole Larghe, Adamello, Italia)

The fabric of fault rocks (existence of foliations, matrix vs fragments ratio, etc.) is one of the parameters which influences the whole mechanic behavior of a fault, since the aseismic to the coseismic phases. In experiments driven in room humid-ity and temperature conditions on the same non cohesive fault rocks, was ob-served that fabric and frictional properties (for example the possibility of enucle-ating seismic ruptures) show an evolution with displacement. Nowadays, data on natural samples regarding the evolution of fabric with displacement are missing. It must be considered that in nature is also present, next to the mechanic role of abrasion and comminution, chemical processes like the fluids action on the rock during fragmentation (mineral dissolution, secondary mineral precipitation, etc.). In this work are studied the fabric and the clast size distribution of fault rocks sampled from the Gole Larghe Fault Zone, Adamello (Southern Alps). The sam-ples selected belong to seismogenic faults with cataclasites and pseudotachilites, which displacement grows from 0 to 9.8 centimeters. These faults were active at the base of the seismogenetic crust (9-11 km depth and 250-280 Celsius). The fabric of the fault rocks is studied from four SEM-BSE images, taken at 100X and 400X magnifications, for each of the two samples. Clast size distribu-tion, shape factors and orientation are going to be calculated using image analysis techniques. The data obtained this way are discussed, also thanks to experimental observations from literature, in order to determine the main deformative process-es undergoing in the fault during the seismic cycle.