Microtectonics of low-P low-T carbonate fault rocks
Book 1 of Geological and geophysical studies of the deep structure of the Earth
Language: English
38.01.00=General Geology 38.15.00=Lithology 38.19.00=Geological and geophysical studies of the deep structure of the Earth 38.45.00=Neotectonics and Tectonics and Seismology Geological and geophysical studies of the deep structure of the Earth Tectonics aapg active advanced stage agosta analysed analysed sample analysed thin-sections angular angular grain apennines aydin basin belt billi billi journal blenkinsop boundary breccia breccia zone bucci bulletin calcite carbonate carbonate fault carbonate rock cataclasis cataclastic cataclastic fabric cavinato central central apennines central italy characterized chipping conduitbarrier permeability contact contact point core corrado cosentino crossed nicols crystal crystal boundary damage damage zone deformation del development dilated stylolite dissolution dissolution structure distribution doi early stage earthquake indicator eds elongated fragment elsevier embryonic embryonic fabric engelder evidence evolution experimental experimental deformation experimental study extension extension fracturing extensional extensional basin extensional fracture fabric faccenna fault fault core fault rock fault slip fault surface fault zone fault-related fault-related deformation faulting figs foreland foreland plate fracture fracture pattern fracturing funiciello gargano geodynamics geological geology geophysical geophysics gouge gouge zone grain grain size hadizadeh host rock hydraulic behaviour hydrocarbon water indicator intermediate intermediate fabric intragranular intragranular extension italy italy journal journal journal geophysical journal structural journal structural geology karst feature keulen storti large grain lithostatic stress logan long long axis main main goal matrix mature mature fabric mechanics mesozoic microscopic mimran mpa natural normal normal fault normal stress nova number observed original original grain paper parallel parallel fault patacca permeability pieri pressure solution process result rock rock column rock strength rossetti rutter salvini sammis sample sample thin-section scale scholz science self-similar cataclasis shear shear deformation shear fracture shear fracturing short sibson site size slip slip sample small grain solution southern southern italy sperlonga site stage storti stress structural structural geology structure studied study surface surface parallel tectonic tectonic environment tectonophysics terra terra nova thin-section thin-section normal thin-sections time tondi toro two-dimensional view typical uid university wenk zone
Published: Dec 31, 2009
Description:
_Journal of Structural Geology 32 (2010) 1392–1402_ Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com locate jsg Microtectonics of low-P low-T carbonate fault rocks Andrea Billi* Dipartimento di Scienze Geologiche, Università ‘‘Roma Tre’’, Largo S. L. Murialdo 1, 00146 Rome, Italy Article info Article history: Received 21 November 2007 Received in revised form 6 May 2009 Accepted 8 May 2009 Available online 19 May 2009 Keywords: Carbonate Fault Fault rock Microtectonics Abstract With the aim of deducing some general microtectonic processes responsible for the development of carbonate fault cores, rock samples were collected in ten of such structures, which are different in size, attitude, kinematics, displacement and tectonic environment. Samples were thin-sectioned and analysed under an optical microscope. Microscopic evidence (i.e., at the scale of tens-to-hundreds of microns) shows that grain size reduction occurred mostly by cataclasis and occasionally by pressure solution. Cataclasis involved three main processes here named intragranular extension fracturing, chipping and shear fracturing. Intragranular extension fracturing is more common in the early stages of cataclasis and produces a coarse breccia consisting of angular grains. In a few cases, pre-existing weaknesses and flaws control the fracture pattern associated with intragranular extension fracturing. Chipping is more common in the advanced stages of cataclasis and produces a gouge consisting of a few survivor rounded grains within a fine matrix. Shear fracturing seems less frequent than the other two processes and usually occurs in the advanced stages of cataclasis. By considering the microscopic and mesoscopic evidence, and the dissimilar frequency of dissolution structures in the analysed fault cores and damage zones, it is inferred that the studied fault zones probably acted as conduit–barrier permeability systems. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Faults in low-pressure low-temperature carbonate rocks are known both as earthquake foci (Amato et al., 1998; Di Bucci and Mazzoli, 2003; Del Gaudio et al., 2007) and as complex permeability structures within hydrocarbon, water and geothermal reservoirs (Eberli et al., 2004; Mancini et al., 2004; Mazzullo, 2004; Celico et al., 2006; Rossetti et al., 2007a,b). Their study at all scales is therefore relevant for structural geologists dealing with seismic faulting or working in the hydrocarbon, water and geothermal industries. Until about 1990, carbonate fault rocks were hardly studied (e.g., Turner et al., 1954; Rutter, 1974; Mimran, 1976, 1977; Friedman and Higgs, 1981) compared to fault-related crystalline and silicoclastic rocks (e.g., Engelder, 1974; Sibson, 1977; Sammis et al., 1986; Sammis and Biegel, 1989; Blenkinsop, 1991). In the last fifteen years, the study of carbonate fault rocks has significantly advanced and become systematic mostly because of its importance in the hydrocarbon industry (Burkhard, 1993; De Bresser and Spiers, 1993; Hadizadeh, 1994; Newman and Mitra, 1994; Babaie et al., 1995; Kennedy and Logan, 1997; Salvini et al., 1999; Graham et al., 2003; Kim et al., 2003; Storti et al., 2003; Llana-Funez and Rutter, 2005). Studies of fault core permeability (Ghisetti et al., 2001; Agosta and Kirschner, 2003; Micarelli et al., 2006; Agosta et al., 2007), grain shape evolution with fault slip (Storti et al., 2007) and some earthquake indicators obtained in laboratory-simulated faults (Han et al., 2007a,b; see Billi and Di Toro, 2008 for a review) have recently improved our understanding of the mechanical and hydraulic behaviour of carbonate fault rocks. In particular, faulting simulations performed at seismic slip rates (about 1 m/s) in Carrara marble revealed very promising results and showed that the seismic (i.e., frictional) process and related indicators have to be investigated at the microscale (Han et al., 2007a,b). Unfortunately, the microtectonics of low-pressure low-temperature fault-related carbonate rocks is still poorly emphasized, and published microscopic images of these rocks are relatively rare (Wenk, 1985; Pieri et al., 2001a,b; Barnhoorn et al., 2004, 2005; Billi, 2005, 2007; Tondi et al., 2006; Tondi, 2007; Billi et al., 2008; Ferrill and Morris, 2008; Mort and Woodcock, 2008). This lack of knowledge prevents advances in the understanding of the processes responsible for the formation of carbonate fault cores and, therefore, in the understanding of the frictional and hydraulic behaviours of these structures. The main goal of this paper is to contribute in knowing and understanding the microscopic processes that are responsible for the development of carbonate fault cores. To reach this goal, A. Billi Journal of Structural Geology 32 (2010) 1392–1402 1393 microscopic images from low-pressure (