Fluid conduits in carbonate‐hosted seismogenic normal faults of central Italy

Abstract

[1] We studied the structures and stable isotope geochemistry of carbonate fault rocks in four normal faults of central Italy. The faults juxtapose Meso-Cenozoic carbonates of the footwalls against continental basins of the hanging walls. Footwall rocks exposed along fault scarps have been exhumed from depths of $1 km. The fault rocks are systematically arranged in each fault and can be separated into five distinct domains. Farthest from the main fault contact are undeformed host rock and fractured host rock (domain 1). Progressively closer to the fault contact, in the core of the fault, are gouge (domain 2), cataclasite (domain 3), and cement-dominated horizons with planar slip surfaces (domain 4). Thin horizons of brecciated hanging wall sediments (domain 5) are adjacent, and locally accreted, to the footwall. Structural and stable isotope data are consistent with compartmentalization of fluid in the faults during exhumation. The data are most consistent with these fluids being predominantly evolved meteoric water rather than fluids from the mantle, crustal magmas, and/or devolatilizing carbonate rocks. Meteoric water infiltrated domains 4 and 5 of the faults, either from hanging wall sediments or directly at the land surface. The gouge and cataclasites of domains 2 and 3 were impermeable barriers to movement of meteoric water into domain 1 and undamaged host rocks of the footwall. The results of this study do not support models of earthquake nucleation and rupture that envision large volumes of deep-seated fluids passing upward through shallow portions of these seismogenic faults.

Hydrogeological properties of fault zones in a karstified carbonate aquifer (Northern Calcareous Alps, Austria)

“…11b) due to secondary dissolution. The present data set unfortunately does not allow to clarify whether cataclasites with higher porosities have elevated permeabilities and if yes, whether a process different from secondary dissolution could be responsible for that; however, examples from the literature treat fine-grained cataclastic rocks as impermeable (Agosta and Kirschner 2003;Agosta et al 2007;Agosta 2008;Storti et al 2003).…”

“…Agosta and Kirschner 2003;Agosta et al 2007;Agosta 2008;Billi and Di Toro 2008;Storti et al 2003). In the damage zone, porosity and permeability are expected to increase and are controlled by connectivity and anisotropy of fracture networks (Agosta et al 2010;Billi 2005b) and/or breccia zones (e.g.…”

Principal Slip Zones in Limestone: Microstructural Characterization and Implications for the Seismic Cycle (Tre Monti Fault, Central Apennines, Italy)

“…The slip zones are normally found within a surrounding fault core tens of centimetres to metres thick containing tabular zones of well-developed fault rock materials often associated with syn-tectonic veining and mineralisation (AGOSTA and KIRSCHNER, 2003;BILLI et al, 2003;CAINE et al, 1996). Surrounding the fault core is a damage zone of fractured host rock that may contain secondary faults but in general does not accommodate high shear strains (CAINE et al, 1996;CHESTER and CHESTER, 1998;CHESTER et al, 2004).…”

Fault zone architecture and deformation processes within evaporitic rocks in the upper crust

“…[3] In spite of the numerous studies of fault zones active within the brittle crust and developed within a large selection of protolith rocks, from crystalline/metamorphic [Chester and Chester, 1998;Faulkner et al, 2003;Wibberley and Shimamoto, 2003;Di Toro and Pennacchioni, 2005] to sedimentary rocks [Shipton and Cowie, 2001;Shipton et al, 2002;Agosta and Kirschner, 2003;Agosta and Aydin, 2006;Micarelli et al, 2006], field studies of fault zones developed within evaporitic rocks, and displaying brittle behavior, are lacking. In particular, evaporitic rocks are commonly known to act as detachment horizons, i.e., plastic behavior [Rutter, 1986] even at low pressures and temperatures, in many fold and thrust belts as for example the Northern Apennines [Bally et al, 1986;Barchi et al, 1998a], the French-Swiss Jura [Muller and Briegel, 1980;Jordan and Nuesch, 1989] and other places around the world [Davis and Engelder, 1985;Harland et al, 1988;Jaume, 1988].…”