HR: 0800h
AN: T51C-0703    [Abstracts]
TI: Fault Zone Architecture and Deformation Processes Within Exhumed Evaporitic Rocks in The Upper Crust
AU: Trippetta, F
EM: fabio.trippetta@unipg.it
AF: GSG, Dipartimento di Scienze della Terra, Universita' di Perugia, P.zza Universita 1, Perugia, 06100, Italy
AU: * De Paola, N
EM: nicola.de-paola@durham.ac.uk
AF: RRG, Earth Sciences Department, University of Durham, South Road, Durham, DH1 3LE, United Kingdom
AU: Collettini, C
EM: colle@unipg.it
AF: GSG, Dipartimento di Scienze della Terra, Universita' di Perugia, P.zza Universita 1, Perugia, 06100, Italy
AU: Faulkner, D
EM: faulkner@liverpool.ac.uk
AF: Rock Deformation Lab, Earth and Ocean Sciences Department, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP, United Kingdom
AB: Evaporitic rocks are generally considered as the ductile decollement horizon for many thrust and fold belts. Recently in the Northern Apennines geophysical data have identified the Triassic Evaporites, TE, as the source region of the major earthquakes of the area (M=6). To characterize fault zone architecture and deformation processes within the TE (anhydrites and dolomites), we have studied exhumed evaporite-bearing normal faults. The geometry and architecture of the fault zones are strongly controlled by both the inherited synorogenic ductile fabric and the different rheological behaviour of the anhydrite (brittle/ductile) and the dolomite (brittle). The interaction between these factors leads to the development of rather complex and heterogeneous fault zone geometry, where complexities within the fault core and the damage zone arise from the juxtaposition of differently deformed domains. Fault rock assemblages are very similar to those of fault zones developed within the brittle regime, and are characterized by fault breccia, gouge and cataclasites of different grain size. In particular, mesoscale damage zones consisting of fractured rocks are wide and well developed within dolomite rocks, whilst they are almost absent or weakly developed within the anhydrite rocks. The fault core of major fault zones (up to 100m displacement) appears zoned with a wider portion of ductile deformation overprinted by an inner and thinner zone of extremely localized brittle deformation. Fault parallel layers of cataclastic dolomite develop within the fault zone and they seem to localize most of the shear strain within the inner brittle zone along well developed principal slip surfaces. We present a mechanical fault evolution model to explain the development of the observed geometry as a function of the interplay between the different rheological behaviour of dolomite and anhydrite and transient fluid pressure increase and release during the fault activity. Our work is relevant to future studies aimed to understand fault controlled reseservoir properties and interpret seismogenic processes associated with other fault zones developed within evaporitic rocks around the world.
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting