IEG 환경지질연구정보센터

광물학│암석학

2011 추계지질과학연합학술발표회 초록집

Petrological and Mineralogical Characteristics of Fault Zone, Yangbuk-myeon, Gyeongju City, Korea

J.M. Lee․S.J. Song․C.O. Choo․Yun D. Jang^*

Department of Geology, Kyungpook National University, [email protected]

This study is focused on faulting and hydrothermal activity of the fault core from the Yangbuk-myeon, Gyeoungju City, Korea. A fault core consists of thin gouge and narrow breccia zones. Intensity of deformation and alteration increases: cataclastic zone, breccia zone, gouge zone depending order. XRD and microscopic analysis have been used to investigate micro- structures and mineralogical changes caused by the faulting and hydrothermal activity asso- ciated with faulting in the fault zones. Fault breccia is composed of quartz (30.2%~32.1%), orthoclase (13.5%~14.2%), albite (12.1%~41.9%), chlorite (7.6%~17.0%) and illite (6.2%~ 25.2%). Fault gouge is composed of quartz (26.6%~50.2%), orthoclase (0%~

14.1%), illite (16.4%~30.5%), chlorite (9.2%~20.8%), kaolinite (0%~7.9%), pyrite (0%~

10.5%) and laumonite (4.1%~9.7%). According to observation of thin-section, the gouge has lots of porphyroclasts composed of old gouge fragments, quartz, feldspar and iron minerals. Clay minerals occurred in matrix show striking S-C foliation characterized by pre- ferred orientation. Fault gouge zone can be divided into greenish brown gouge and bluish gray gouge on the basis of color. There are microstructural differences between bluish gray gouge and greenish brown gouge. Greenish brown gouge has much clay minerals, smaller in size and number of porphyroclasts than bluish gray gouge. Greenish brown gouge has abun- dant iron minerals such as hematite, while chiefly pyrite in bluish gray gouge. Multiple faulting shows evidence of multiple displacement features of quartz, feldspar, porphyroclasts in the matrix. Hydrothermal alteration features are observed in the gouge with the dispersion of dissolved components into the matrix at the grain margins of minerals with occurrence of clay minerals such as laumonite, illite and chlorite.

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