Structural architecture and paleofluid evolution in fault zones dissecting ramp anticlines: examples from the Lunigiana region (Northern Apennines) and the Gran Sasso Massif (Central Apennines), Italy

Abstract

The role of fluids in earthquake mechanics is a topic receiving increasing attention in the last decades due to the detected cause-effect relationships between rapid fluid pressure variations and migration along fault zones, and seismic event occurrences. Their complex interplay depends on the structural and permeability architectures of fault systems, deformation mechanisms and rates, environmental conditions of deformation (lithostatic, pore fluid, and tectonic pressure, and temperature), protolith and fault zone lithology and mechanical stratigraphy, and tectonic setting. Within this context, regional-scale fault systems exert a primary control on the fluid flow pattern, allowing either fluid redistribution and mixing on large scales through highly permeable structural elements, or promoting fluid compartmentalization and sealing when they are characterized by low permeability structural elements, or both. In the Apennines orogenic wedge, high-angle extensional fault systems dissecting ramp anticlines are associated with intense seismicity or are potential sesismogenetic sources and promote vertical fluid migration from shallow to deep crustal levels and vice versa. For this reason, their study has social, economic and scientific importance. This Ph.D. Thesis investigates on the structural architecture and paleofluid evolution of well exposed fault zones dissecting ramp anticlines in the Northern and Central Apennines. The study was performed with a multidisciplinary approach, to characterize structural and diagenetic processes during fault evolution, with particular attention on the seismological and hydrogeological implications. In the Northern Lunigiana region, Northern Apennines, we studied extensional deformation structures which progressively formed during the development of a regional-scale extensional fault system in the Tyrrhenian Sea side of the orogenetic belt, where the metamorphic basement was previously affected by multiple thrusting events and supplied hot fluids which migrated upward through the sedimentary cover. The Gran Sasso Massif, in the Central Apennines displays outstanding exposures of a thrustfold stack that allowed us to investigate on the paleofluid evolution of both extensional and contractional fault systems, which developed in the axial sector of the orogenic belt, where fast uplift rates promoted meteoric fluids infiltration into the shallow crust.