HR: 1330h
AN: T12C-0465    [PDF]
TI: Natural Occurrences of Surface Melting in the Slickensides of the Fault Zone in Miaoli Area, Western Taiwan
AU: * Song, S
EM: srsong@ntu.edu.tw
AF: Institute of Geosciences, National Taiwan University, 245 Choushan Road, Taipei, 106 Taiwan
AU: Kou, L
AF: Institute of Geosciences, National Taiwan University, 245 Choushan Road, Taipei, 106 Taiwan
AB: Slickensides are non-penetrative smoothed or polished surface normally developed on movement planes of fault zone, or between rock layers folded by flexural slip. Experimental evidence suggests that naturally silckenside formation may be widely originated by surface melting in the relatively dry faulting (Spray, JSG, 1989). However, due to the modification by fluid alteration or via various co-seismic and interseismic events, evidence of melting has not yet been unequivocally found in natural slickensides. This research reports an unambiguous pseudotachylyte occurred in the slickensides formed by surface melting in the fault zone of Miaoli area, west Taiwan. Taiwan is located in the young orogenic belt, which the fault-related earthquakes were very common and severe in last few million years. The faults, especially for the thrust faults, thus, are widely distributed in the Island. The pseudotachylyte occurred in the slickenside surface of the fault zone have been found in the drilled core, about 500 meters in depth below the surface in the western foothill sedimentary sequences of Miaoli area, west Taiwan. Two types of surface feature, well-polished shiny surface as mirror and scrape furrow or striated coatings can be found in the surface of slickensides. The former mostly occurred in the fine sandstones to siltstones, while the later mainly found in the coarse sandstones. It clearly suggests that the surface features may be originated by the asperity during the comminution in the slickenside formation. Petrographically, the slickensides are dominantly composed of fault gouge and cataclasites with or without preferred orientated micas. The pseudotachylytes are thin, submillimeter to millimeter in thickness and dominantly occur on the surface of slickenside of fault zone. Optical and scanning and transmission electron microscopies reveal that the pseudotachylytes are very fresh and dominantly consist of black or dark brown, fine-grained to glassy aphanitic matrix with microlites, rounded or embayed clasts and numerous rock and mineral fragments. The presences of well fresh pseudotachylyte and surface melting in the slickensides strongly indicate that the fault zone in the Miaoli area, west Taiwan is very dry condition during or after rapid seismic faulting.
UR: http://www.gl.ntu.edu.tw/
DE: 7209 Earthquake dynamics and mechanics
DE: 8100 TECTONOPHYSICS
DE: 8107 Continental neotectonics
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting