Deformation features in fault zone involving carbonates rocks: the Gubbio fault (Italy)

Maura Bussolotto, Dept. Sciences de la Terre, Université Paris XI, UMR 7072, 91405 Orsay, France, [email protected]

This works aims to better understand deformation mechanisms which occur in fault zones involving carbonates rocks, and the main factors (i.e. P/T condition, fault displacement, lithology) that control them. The study actually focalizes on the Gubbio normal fault which exposes excellent outcrops. The Gubbio fault is a NW-trending normal fault, which juxtaposes the Plio-Quaternary basin-fill deposits of the hangingwall against the folded Mesozoic limestones of the footwall. This study combines outcrop-scale structural analysis, optical and cathodoluminescence microscopy analysis, fluid inclusion microthermometry and stable isotope analysis. We also try to reconstruct fault displacement by stratigraphic analysis. Fault zone is characterized by six main N-E dipping fault planes separating seven well defined structural domains. First observations indicate that each domain, from the inner (footwall) to the external (hanginwall) part of the fault, is characterized by mechanisms (strike slip veins, hydraulic breccias, random fabric breccias, foliated cataclasites, shear and extensional veins and dissolution seams) well organized and located along the fault zone. First results from fluid inclusions microthermometry indicate that this process occurred at low P/T conditions. Geochemical analyses show that synkinematic calcites are precipitated from two fluids of different origin both in equilibrium with host rocks and not influenced by meteoric water from surface. Stratigraphic analyses indicate that the observed fault displacement is less than 400m of offset. Following work focalises in the evaluation and quantification of the role of each parameters of control of deformation.