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조규환;다카기히데오;이와무라아키라;아와지도타;장태우;손승완;이타야테츠마루;오카다도시노리
- Economic and Environmental Geology
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- v.34 no.6
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- pp.583-593
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- 2001
Clay minerals are common component of fault gouge and have been used to determine the fault activity age using K-Ar dating technique. We carried out XRD and K-Ar analyses of the mica clay minerals from the fault gouge along the Ulsan Fault Zone, southeastern Korea to estimate the timing of the major fault activity. Mica clay minerals for four grain size fractions of 5-2 Um, 2-1 $\mu$m, 1-0.35$\mu$m, and 0.35-0.05 $\mu$m were separated from the gouge samples in the three locations by the hydraulic elutriation and contrifugal separator. Fault gouges are composed of smectite, mica clay minerals, kaolinite, chlorite, quartz, and feldspar. The illite crystallinity of mica clay minerals is the highest in the finest grained fraction with lM polytype, indicating that the aulhigenic mica clay minerals have been concentrated in the fraction. K-Ar ages give some variation from 46 to 35 Ma (330-2), 45 to 39 Ma (16Ww), and 32 to 15 Ma (102Ws) and are the youngest in the finest grained fraction. These results suggest that the hydrothermal alteration associated with the major fault activities along the Ulsan fault Zone took place twice at 39-35 Ma and 15 Ma.
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