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Clay mineral anomalies in the fault zone of the Chelungpu Fault, Taiwan, and their implications
Author(s) -
Kuo LiWei,
Song ShengRong,
Yeh EnChao,
Chen HueiFen
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039269
Subject(s) - geology , illite , clay minerals , fault gouge , fault (geology) , chlorite , kaolinite , seismology , geochemistry , mineralogy , quartz , paleontology
The Taiwan Chelungpu‐fault Drilling Project (TCDP) Hole‐A recovered continuous core samples across the rupture zone of the 1999 Chi‐Chi earthquake (Mw7.6). Studying in‐situ chemical properties sequentially from fresh‐fault‐zone materials of the Chelungpu fault provides insight into possible faulting mechanisms. Distinct anomalies of mineral assemblages at the 1111‐m fault zone of TCDP Hole‐A are found to be: (1) A decrease in clay content within the primary slip zone (PSZ); and (2) A significant decline of illite, disappearance of chlorite and kaolinite, and spike in smectite within the PSZ. Meanwhile, features relating to melting or amorphous material in the PSZ have been observed by SEM and TEM. The results suggest that the PSZ might have experienced generation of glassy materials such as pseudotachylyte by the expense of clay minerals due to strong shear heating, then prompt alteration of pseudotachylyte into smectite. Characteristics of clay minerals and images obtained from electronic microscopes in the PSZ thus imply that pseudotachylyte possibly developed during the 1999 Chi‐Chi earthquake, but quickly altered into smectite. This particular phenomenon may explain why pseudotachylyte is rarely found in exhumed hydrated fault zones.