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Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 1. Signatures within the Deep Wenchuan Earthquake Fault Zone and Their Implications
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Minerals 2018, 8(9), 393; https://doi.org/10.3390/min8090393

Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 2. Characterization of Fault Gouge from Deep Drilling and Implications for Fault Maturity

1
Department of Earth Sciences, National Central University, Taoyuan 320, Taiwan
2
Department of Earth Sciences, National Taiwan Normal University, Taipei 106, Taiwan
3
National Taiwan Museum, Taipei 100, Taiwan
4
Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
5
Department of Geosciences, National Taiwan University, Taipei 106, Taiwan
*
Author to whom correspondence should be addressed.
Received: 22 June 2018 / Revised: 4 September 2018 / Accepted: 5 September 2018 / Published: 7 September 2018
(This article belongs to the Special Issue Mineralogy of Natural Graphite)
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Abstract

In recent works on the determination of graphitization of carbonaceous materials (CM) within the principal slip zone (PSZ) of the Longmenshan fault (China), we demonstrated that the formation of graphite, resulted from strain and frictional heating, could be evidence of past seismic slip. Here we utilize Raman Spectroscopy of CM (RSCM) on the CM-bearing gouges in the fault zone of the Longmenshan fault belt, at the borehole depth of 760 m (FZ760) from the Wenchuan earthquake Fault Scientific Drilling project-1 (WFSD-1), to quantitatively characterize CM and further retrieve ancient fault deformation information in the active fault. RSCM shows that graphitization of CM is intense in the fault core with respect to the damage zone, with the graphitized carbon resembling those observed on experimentally formed graphite that was frictionally generated. Importantly, compared to the recognized active fault zone of the Longmenshan fault, the RSCM of measured CM-rich gouge shows a higher degree of graphitization, likely derived from high-temperature-perturbation faulting events. It implies that FZ760 accommodated numerous single-event displacement and/or at higher normal stresses and/or in the absence of pore fluid and/or along a more localized slip surface(s). Because graphite is a well-known lubricant, we surmise that the presence of the higher degree graphitized CM within FZ760 will reduce the fault strength and inefficiently accumulate tectonic stress during the seismic cycle at the current depth, and further infer a plausible mechanism for fault propagation at the borehole depth of 590 m during the Mw 7.9 Wenchuan earthquake. View Full-Text
Keywords: graphitization; carbonaceous material; Longmenshan fault; Wenchuan earthquake; WFSD-1 graphitization; carbonaceous material; Longmenshan fault; Wenchuan earthquake; WFSD-1
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Kuo, L.-W.; Huang, J.-R.; Fang, J.-N.; Si, J.; Song, S.-R.; Li, H.; Yeh, E.-C. Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 2. Characterization of Fault Gouge from Deep Drilling and Implications for Fault Maturity. Minerals 2018, 8, 393.

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