X-RAY DIFFRACTION ANALYSIS RESULT OF CO-SEISMIC FAULT GOUGE IN CARBON MUDSTONE AT OUTCROPS OF BAJIAOMIAO AND SHENXIGOU IN HONGKOU

doi:10.3969/j.issn.0253-4967.2012.01.003

Abstract

Abstract:

The co-seismic surface ruptures of the May 12,2008 Wenchuan earthquake in Bajiaomiao and Shengxigou were developed mainly at the outcrops of carbon mudstones of Xujiahe formation of Triassic system. The black color and textures of co-seismic gouge are similar to old gouge and bed rock. We excavated trenches along the surface ruptures and collected samples of wall rock, fault breccia, old fault gouge and co-seismic gouge. All samples were analyzed quantitatively by X-ray diffraction. The main rock-forming minerals and clay minerals of co-seismic gouge are similar to old gouge, but their content is different, which shows the co-seismic gouge was formed based on old gouge. The wall rock and fault breccias adjacent to co-seismic gouge are carbon mudstones. The mineral composition and texture of the fault zone are obviously simpler than that of the northern part of the surface ruptures of Yinxiu-Beichuan Fault. The major minerals of co-seismic gouge are quartz and clay minerals, containing a few amount of feldspar, without calcite; a small amount of dolomite was found in co-seismic gouge at Shenxigou, and the content of dolomite is much lower than that in bed rock and old gouge. The marked character of new gouge is abundant in clay minerals, and the content of clay minerals decreases in turn from co-seismic gouge to old fault gouge, fault breccia and wall rock. The main clay minerals are illite and illite/smectite (I/S) mixed layer, containing a few amount of chlorite; a few kaolinite was found in co-seismic gouge of Shenxigou, the bed rock and gouge of Bjiaomiao did not contain kaolinite. Mineral characters of co-seismic gouge are different from old gouge. The old gouge contains calcite and dolomite, and the co-seismic gouge contains a few amount of dolomite and without calcite; the old gouge does not contain illite. However, for co-seismic gouge, mineral characters are different between black and white gouges, the content of illite in black gouge is higher than that in white gouge. In this study, the main clay minerals are I/S mixed layer, illite and chlorite, which is similar with San Andreas Fault and Chelunpu Fault. However, kaolinite content is extremely low in this fault, only trace kaolinite was found in the co-seismic gouge of Shenxigou. The high content of I/S in co-seismic gouge shows that the rich K+fluid participated in the seismic fault slip. All of these characters show that minerals of co-seismic fault gouge in this study are somewhat different with that of San Andreas Fault and Chelunpu Fault.

Key words: Wenchuan earthquake, co-seismic gouge, X-ray diffraction quantitative analysis, clay mineral

摘要：

5.12汶川地震同震地表破裂带在虹口八角-深溪沟一带主要出露于三叠系须家河组的炭质泥岩中,同震断层泥在颜色、结构上与老断层泥和围岩类似。通过开挖探槽,系统采样,采用粉晶X射线衍射定量分析方法,研究了同震地表破裂带的围岩、断层角砾岩、老断层泥和新断层泥的矿物成分特征。同震断层泥的主要成分为石英和黏土矿物,含微量长石和白云石;断层泥的显著特征为高黏土矿物含量,从同震断层泥、老断层泥、角砾岩到围岩黏土矿物含量依次降低,黏土矿物以伊利石和伊蒙混层为主,含微量绿泥石和高岭石,矿物组成明显比地表破裂带北段同震断层泥简单。不同颜色的同震断层泥成分略有不同,黑色断层泥中伊利石含量明显高于白色断层泥;老断层泥中含有方解石和白云石,而同震断层泥不含方解石,只含微量白云石。同震断层泥中伊蒙混层高含量表明,在本次地震错动中有富含K的流体参与。

关键词: 汶川地震, 同震断层泥, 粉晶X射线衍射定量分析, 黏土矿物

CLC Number:

P315.2

DANG Jia-xiang, ZHOU Yong-sheng, HAN Liang, HE Chang-rong, CHEN Jian-ye, DANG Xin-zeng, YANG Xiao-song. X-RAY DIFFRACTION ANALYSIS RESULT OF CO-SEISMIC FAULT GOUGE IN CARBON MUDSTONE AT OUTCROPS OF BAJIAOMIAO AND SHENXIGOU IN HONGKOU[J]. SEISMOLOGY AND GEOLOGY, 2012, 34(1): 17-27.

党嘉祥, 周永胜, 韩亮, 何昌荣, 陈建业, 党新增, 杨晓松. 虹口八角庙-深溪沟炭质泥岩同震断层泥的X射线衍射分析结果[J]. 地震地质, 2012, 34(1): 17-27.

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