Analisi di immagine di rocce di faglia in carbonati (faglia di Tre Monti, Appennino Centrale, Italia).

Active seismic fault can be hosted in carbonate, an important lithology not only in Central Italy but in many other seismically active area. Thus the study of structure on slip zone that cut limestone host rock, such as the ‘clast-cortex grain’, peculiar rounded grains consisting of a central (often angular) clast wrapped by a laminated outer cortex of ultra-fine-grained calcite, can be useful for the understanding of localized deformation processes occurring during the seismic cycle. (Smith el Al. 2011) In this work is studied a sample from the Tre Monti normal fault, Central Appennines, (Italy) an active fault that cuts limestone, with an exumation from <2Km dept, where ambient temperature << 100°. The fabric of the slip zone, which can be divided in two distinct layers, is studied from a scanned image of the thin section, photo and photo-mosaic taken using optical microscope. Clast size distribution, orientation and shape descriptor are calculated using image analysis techniques. The results obtained are then discussed. The Clast Size Distribution obtained suggest that a rework of the cataclasite is needed to obtain the microstructure defined as clast cortex grains. The (probably) co-seismic rolling of angular clast would lead to the formation of the clast cortex grain, with a minimum on the frammentation.