HR: 0800h
AN: T11D-1315    [Abstracts]
TI: Characterizing Brittle Deformation, Damage Parameters, and Clay Composition in Fault Zones: Insights From the Chelungpu and Mozumi Faults
AU: * Isaacs, A J
EM: angela.isaacs@usu.edu
AF: Utah State University, Department of Geology 4505 Old Main Hill, Logan, UT 84322-4505 United States
AU: Evans, J P
EM: jpevans@cc.usu.edu
AF: Utah State University, Department of Geology 4505 Old Main Hill, Logan, UT 84322-4505 United States
AB: Six outcrop sites along strike of the Chelungpu Fault (CF), Taiwan are compared with core samples through the CF zone and the Mozumi fault zone, Japan to evaluate how mesostructural and microstructural scale fault properties and clay mineralogy change as a function of strike, structural depth, and in different components of a fault zone. Characterization of core and outcrop samples will determine fluid flow properties and processes, and determine seismological processes at each study site. X-ray diffraction analysis shows an increase in smectite towards the CF at or very near the surface, and an increase in illite toward the fault at depth. Weathering and increased fluid flow in the exhumed fault zone plays an important role in the composition of the clay, but is enhanced in the clay gouge because of fabrics created by faulting. Weathering profiles based on samples and general weathering models for Taiwan-type climate will be used to determine the extent to which weathering plays a role in surficial fault gouge composition. The abundance of gouge, the dominance of smectite in outcrop samples, and the intensity of fault related damage at outcrop and microstructural scales increase in southern portions of the CF. Samples from the southern CF show almost no intact host rock as well as cross cutting relationships of veins, fractures, and foliated gouge suggesting multiple deformation events. Samples from the northern CF show mostly intact host rock with some unfoliated or weakly foliated clay. The southern portion of the CF is most likely older and has accumulated more damage relative to the north. Shale and clay-rich fault zones are not typically well preserved due to the ease with which they weather, and are therefore not well studied at the microstructural and outcrop scale. The Chelungpu and Mozumi faults provide a valuable opportunity to characterize shale and clay-rich fault zones. These fault zones may control fluid flow and distribution of fault-zone seismic waves differently than fault zones in crystalline rocks due to clay properties. Studies of fault zone properties provide important constraints for geologic modeling, and clay mineralogy and microstructures may control the role of fault core and damage zone as conduits or barriers to fluid flow.
DE: 5112 Microstructure
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting