HR: 0800h
AN: T41B-0576    [Abstracts]
TI: Structural Analysis of the Exhumed SEMP Fault Zone, Austria: Towards an Understanding of the Mechanics of Shear Zone Localization
AU: * Frost, E K
EM: efrost@usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089, United States
AU: Dolan, J F
EM: dolan@usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089, United States
AU: Sammis, C G
EM: sammis@usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089, United States
AU: Hacker, B
EM: hacker@geol.ucsb.edu
AF: University of California at Santa Barbara, Department of Earth Science University of California Webb Hall, BLDG 526, Santa Barbara, CA 93106, United States
AU: Ratschbacher, L
EM: lothar@geo.tu-freiberg.de
AF: Technische Universität Bergakademie Freiberg, Bernhard-von-Cottastr. 2, Freiberg, D- 09596, Germany
AU: Decker, K
EM: kurt.decker@univie.ac.at
AF: Universität Wien, Althanstrasse 14, Vienna, 1090, Austria
AU: Cole, J
EM: telejosh@gmail.com
AF: University of California at Santa Barbara, Department of Earth Science University of California Webb Hall, BLDG 526, Santa Barbara, CA 93106, United States
AB: One of the most exciting frontiers in earthquake science is the linkage between the internal structure and mechanical behavior of fault zones. Little is known about how fault-zone structure varies as a function of depth, yet such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria, a major left-lateral strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. In order to establish the structure of this fault zone, we are studying outcrops at a variety of exhumation levels, from <1 km near the eastern end of the fault, downward through the seismogenic crust, across the brittle- ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present new results and discuss the mechanical implications of these new data from two key outcrops at Gstatterboden and Taxenbach, where the SEMP has experienced 40-60 km of displacement. The outcrop at Gstatterboden has been exhumed from 2-3 km depth. Here the SEMP juxtaposes limestone of the Wettersteinkalk on the south with dolomite of the Ramsaudolomit on the north. Faulting has produced extremely asymmetric damage, extensively shattering and shearing the dolomite while leaving the limestone largely intact. We interpret this brittle damage using both mesoscopic calculations of damage intensity and microscopic grain size distribution analysis, which suggests that shear has localized to a zone approximately 10 m wide. These findings are compared to the brittle-ductile outcrop at Taxenbach, which has been exhumed from depths of up to 10 km. Here, the SEMP juxtaposes Greywacke Zone rocks with carbonate mylonites of the Klammkalk. Microstructural observations of grain size and lattice preferred orientation suggest a marked increase in strain within 100 m of the lithologic contact, although the first-order observation is that most of the 60 km of total displacement has localized along the contact between these units, suggesting that to first order, strain at the base of the brittle-ductile transition is extremely localized.
DE: 3625 Petrography, microstructures, and textures
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: 2007 Fall Meeting