HR: 0800h
AN: T51A-1314    [Abstracts]
TI: Fluid Infiltration After Seismic Faulting: Chemical And Mineralogical Compositions Of Fault Rocks From The Active Chelungpu Fault
AU: * Chen, W D
EM: dc@geps.gep.ncu.edu.tw
AF: Department of Earth Sciences, National Central University, 300, Chungda Rd., Chungli, chungli, 32001 Taiwan
AU: Lee, W
T51A-1314 AF: Department of Earth Sciences, National Central University, 300, Chungda Rd., Chungli, chungli, 32001 Taiwan
AU: Tanaka, H
T51A-1314 AF: Department of Earth and Planetary Sciences, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, Tokyo, 113-003 Japan
AU: Lee, C
T51A-1314 AF: Department of Geosciences, National Taiwan University, Sec. 4, Roosevelt Rd, Taipei, 106 Taiwan
AU: Wang, C
T51A-1314 AF: Department of Earth Sciences, National Central University, 300, Chungda Rd., Chungli, chungli, 32001 Taiwan
AB: In order to understand the fault zone architecture and the mechanism that caused the Chi-Chi earthquake, a Chelungpu drilling project was conducted from January 2004. In this study, the chemical and mineralogical variations between the historical fault zone and the fault zone caused by the Chi-Chi earthquake and, also the variations between undamaged rocks and fault rocks are examined. It is found that the slope of TiO2 immobile isocon is always larger than the constant mass isocon either in the isocon diagram analyses for comparing the host rocks with the rocks from the damaged zone or with the gouges in the center of the fault zone. This indicates that volume loss occurs both in the damaged zone and the fault core. These results strongly imply that pervasive fluid infiltration occurred within the fault zone. Volume loss within the damaged zone and fault core is interpreted to result from a two-stage process involving: (i) coseismic mechanical wearing and/or dissolution in the fault core, and (ii) fluid infiltration within the fault zone during postseismic and interseismic periods along cracks caused by seismic failure. The greater volume loss in the fault core could result from the moderate permeability and the very fine grain nature of the pulverized mineral grain in the fault core, which enhances the chemical reactions including the transformation of feldspars and muscovite to the clay minerals. The isocon diagram analysis by XRF data and clay mineral data indicate that pervasive fluid infiltration has occurred and probably played a significant role in changing the mineralogical and chemical architecture of the fault zones caused by the cyclic earthquakes.
DE: 8010 Fractures and faults
SC: Tectonophysics [T]
MN: Fall Meeting 2005