HR: 11:35h
AN: S52A-06    [Abstracts]
TI: Fossil fluid reservoir beneath a duplex fault structure within the Central Range of Taiwan: implication for earthquake rupturing by leakage and volatilization of confined metamorphic fluid at depth
AU: * Okamoto, K
EM: kazu@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec.2, Nankang, Taipei, 115 Taiwan
AU: Chan, Y
EM: yuchang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec.2, Nankang, Taipei, 115 Taiwan
AU: Yui, T
EM: tfyui@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec.2, Nankang, Taipei, 115 Taiwan
AU: Iizuka, Y
EM: yiizuka@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec.2, Nankang, Taipei, 115 Taiwan
AU: Chu, H
EM: chuht@moeacgs.gov.tw
AF: Central Geological Survey, MOEA, Taiwan, 2 Ln. 109, Huahsing Street, Chungho, Taipei, 235 Taiwan
AB: We investigated the central part of the Taiwan slate belt and discovered potential fossil fluid reservoirs beneath a duplex fault structure. We described the occurrence of the fossil fluid reservoirs, examined microstructures of the highly silicified zones, and microprobed the veining minerals within the reservoirs. The investigation was driven by better understanding the mechanisms which likely facilitated the speedy rupturing process of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake. We examined exposed rocks in regions, where the pressure and temperature conditions mostly resemble the hypocenter of the Chi-Chi earthquake, i.e., about sub-greenschist facies. Field observations and composition analyses of the silicified vein-rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep-seated fluids. These fluids most likely come from the Taiwan metamorphic complex at depths by the dehydration and decarbonation reactions (or partial melting). The presence of albite, K-feldspar, calcite and traces of REE minerals (monazite, and rutile) within the analyzed veins indicates a high-temperature metamorphic origin of the fluids. In addition, the gouge zone of a link fault above the detachment also indicates the presence of high-pressure fluids during faulting. To explain these observations, it is probable that episodic leakage of the confined fluid pockets may provide essential fluids for fault lubrication during earthquake rupturing. After leakage and subsequent volatilization of gases, the volatile fluids injected into earthquake fault planes and significantly ease the earthquake rupturing process
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
DE: 8105 Continental margins and sedimentary basins
DE: 7209 Earthquake dynamics and mechanics
DE: 3660 Metamorphic petrology
SC: Seismology [S]
MN: 2004 AGU Fall Meeting