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Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks
Kouketsu, Y; Shimizu, I; Wang, Y; Yao, L; Ma, SL; Shimamoto, T
2017
Source PublicationTECTONOPHYSICS
ISSN0040-1951
Volume699Issue:-Pages:129-145
Subtype期刊论文
Abstract

We analyzed micro-Raman spectra of carbonaceous materials (CM) in natural and experimentally deformed fault rocks from Longmenshan fault zone that caused the 2008 Wenchuan earthquake, to characterize degree of disordering of CM in a fault zone. Raman spectral parameters for 12 samples from a fault zone in Shenxigou, Sichuan, China, all show low-grade structures with no graphite. Low crystallinity and delta C-13 values (-24%o to -25%) suggest that CM in fault zone originated from host rocks (Late Triassic Xujiahe Formation). Full width at half maximum values of main spectral bands (D1 and D2), and relative intensities of two subbands (D3 and D4) of CM were variable with sample locations. However, Raman parameters of measured fault rocks fall on established trends of graphitization in sedimentary and metamorphic rocks. An empirical geothermometer gives temperatures of 160-230 degrees C for fault rocks in Shenxigou, and these temperatures were lower for highly sheared gouge than those for less deformed fault breccia at inner parts of the fault zone. The lower temperature and less crystallinity of CM in gouge might have been caused by the mechanical destruction of CM by severe shearing deformation, or may be due to mixing of host rocks on the footwall. CM in gouge deformed in high-velocity experiments exhibits slight changes towards graphitization characterized by reduction of D3 and D4 intensities. Thus low crystallinity of CM in natural gouge cannot be explained by our experimental results. Graphite formation during seismic fault motion is extremely local or did not occur in the study area, and the CM crystallinity from shallow to deep fault zones may be predicted as a first approximation from the graphitization trend in sedimentary and metamorphic rocks. If that case, graphite may lower the friction of shear zones at temperatures above similar to 300 degrees C, deeper than the lower part of seismogenic zone. (C) 2017 Elsevier B.V. All rights reserved.

KeywordCarbonaceous Material Raman Spectroscopy Fault Rock Longmenshan Thrust Belt Wenchuan Earthquake Friction Experiment
DOI10.1016/j.tecto.2017.01.015
Indexed BySCI
Language英语
WOS IDWOS:000395611700009
Citation statistics
Document Type期刊论文
Identifierhttp://ir.sinap.ac.cn/handle/331007/27430
Collection中科院上海应用物理研究所2011-2018年
Recommended Citation
GB/T 7714
Kouketsu, Y,Shimizu, I,Wang, Y,et al. Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks[J]. TECTONOPHYSICS,2017,699(-):129-145.
APA Kouketsu, Y,Shimizu, I,Wang, Y,Yao, L,Ma, SL,&Shimamoto, T.(2017).Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks.TECTONOPHYSICS,699(-),129-145.
MLA Kouketsu, Y,et al."Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks".TECTONOPHYSICS 699.-(2017):129-145.
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