Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi-Chi earthquake (Mw 7.6, 1999): Evidence for frictional heating and co-seismic fluids

Yu Min Chou, Sheng Rong Song, Charles Aubourg, Yen Fang Song, Anne Marie Boullier, Teh Quei Lee, Mark Evans, En Chao Yeh, Yi Ming Chen

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

During an earthquake, physical and chemical transformations lead to alteration and formation of minerals in the gouge layer. Altered and neoformed minerals can be used as tracers of some earthquake processes. In this study, we investigate pyrite and magnetic minerals within the host Chinshui siltstone and the 16-cm-thick gouge. This gouge hosts the principal slip zone of Chi-Chi earthquake (Mw 7.6, 1999). In the Chinshui siltstone, pyrite framboids of various sizes and euhedral pyrite are observed. The magnetic mineral assemblage comprises stoichiometric magnetite, greigite, and fine-grained pyrrhotite. The pyrite content is generally reduced in the gouge compared to the wall rock. The magnetic mineral assemblage in the gouge consists of goethite, pyrrhotite, and partially oxidized magnetite. The pyrrhotite, goethite and some magnetite are neoformed. Pyrrhotite likely formed from high temperature decomposition of pyrite (>500C) generated during co-seismic slip of repeated earthquakes. Goethite is inferred to have formed from hot aqueous co-seismic fluid (>350C) in association with the 1999 Chi-Chi event. Elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite. We suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment-derived fault gouge.

Original languageEnglish
Article numberQ08002
JournalGeochemistry, Geophysics, Geosystems
Volume13
Issue number8
DOIs
Publication statusPublished - 2012 Aug 1

Fingerprint

magnetic mineral
pyrites
pyrrhotite
Ferrosoferric Oxide
Minerals
fault zone
pyrite
Earthquakes
earthquakes
minerals
heating
Heating
earthquake
magnetite
Fluids
fluid
fluids
goethite
slip
siltstone

Keywords

  • Chi-Chi earthquake
  • TCDP
  • gouge
  • pyrite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi-Chi earthquake (Mw 7.6, 1999) : Evidence for frictional heating and co-seismic fluids. / Chou, Yu Min; Song, Sheng Rong; Aubourg, Charles; Song, Yen Fang; Boullier, Anne Marie; Lee, Teh Quei; Evans, Mark; Yeh, En Chao; Chen, Yi Ming.

In: Geochemistry, Geophysics, Geosystems, Vol. 13, No. 8, Q08002, 01.08.2012.

Research output: Contribution to journalArticle

Chou, Yu Min ; Song, Sheng Rong ; Aubourg, Charles ; Song, Yen Fang ; Boullier, Anne Marie ; Lee, Teh Quei ; Evans, Mark ; Yeh, En Chao ; Chen, Yi Ming. / Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi-Chi earthquake (Mw 7.6, 1999) : Evidence for frictional heating and co-seismic fluids. In: Geochemistry, Geophysics, Geosystems. 2012 ; Vol. 13, No. 8.
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