Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids
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 siltsto...
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2012-08-01
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| Series: | Geochemistry, Geophysics, Geosystems |
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| Online Access: | https://doi.org/10.1029/2012GC004120 |
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| author | 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 |
| author_facet | 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 |
| author_sort | Yu‐Min Chou |
| collection | DOAJ |
| description | 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 (Mw7.6, 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 (>500°C) generated during co‐seismic slip of repeated earthquakes. Goethite is inferred to have formed from hot aqueous co‐seismic fluid (>350°C) 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. |
| format | Article |
| id | doaj-art-171b9b066a0848babddf8a1fc5c9a8f4 |
| institution | Matheson Library |
| issn | 1525-2027 |
| language | English |
| publishDate | 2012-08-01 |
| publisher | Wiley |
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| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj-art-171b9b066a0848babddf8a1fc5c9a8f42025-07-24T04:46:01ZengWileyGeochemistry, Geophysics, Geosystems1525-20272012-08-01138n/an/a10.1029/2012GC004120Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluidsYu‐Min Chou0Sheng‐Rong Song1Charles Aubourg2Yen‐Fang Song3Anne‐Marie Boullier4Teh‐Quei Lee5Mark Evans6En‐Chao Yeh7Yi‐Ming Chen8Department of Geosciences, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 106, TaiwanDepartment of Geosciences, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 106, TaiwanAssociated International Laboratory, Active Deformation and Environment Programme for Taiwan, National Science Council, 106, Sec. 2, Heping East Road, Taipei 106, TaiwanNational Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, TaiwanAssociated International Laboratory, Active Deformation and Environment Programme for Taiwan, National Science Council, 106, Sec. 2, Heping East Road, Taipei 106, TaiwanAssociated International Laboratory, Active Deformation and Environment Programme for Taiwan, National Science Council, 106, Sec. 2, Heping East Road, Taipei 106, TaiwanDepartment of Physics and Earth Science, Central Connecticut State University, New Britain, Connecticut 06050, USAAssociated International Laboratory, Active Deformation and Environment Programme for Taiwan, National Science Council, 106, Sec. 2, Heping East Road, Taipei 106, TaiwanNational Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, TaiwanDuring 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 (Mw7.6, 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 (>500°C) generated during co‐seismic slip of repeated earthquakes. Goethite is inferred to have formed from hot aqueous co‐seismic fluid (>350°C) 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.https://doi.org/10.1029/2012GC004120Chi‐Chi earthquakeTCDPgougepyrite |
| spellingShingle | 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 Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids Geochemistry, Geophysics, Geosystems Chi‐Chi earthquake TCDP gouge pyrite |
| title | Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids |
| title_full | Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids |
| title_fullStr | Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids |
| title_full_unstemmed | Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids |
| title_short | Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids |
| title_sort | pyrite alteration and neoformed magnetic minerals in the fault zone of the chi chi earthquake mw7 6 1999 evidence for frictional heating and co seismic fluids |
| topic | Chi‐Chi earthquake TCDP gouge pyrite |
| url | https://doi.org/10.1029/2012GC004120 |
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