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Title: Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples

Abstract

The microstructures, mineralogy and chemistry of representative samples collected from the cores of the San Andreas Fault drill hole (SAFOD) and the Taiwan Chelungpu-Fault Drilling project (TCDP) have been studied using optical microscopy, TEM, SEM, XRD and XRF analyses. SAFOD samples provide a transect across undeformed host rock, the fault damage zone and currently active deforming zones of the San Andreas Fault. TCDP samples are retrieved from the principal slip zone (PSZ) and from the surrounding damage zone of the Chelungpu Fault. Substantial differences exist in the clay mineralogy of SAFOD and TCDP fault gouge samples. Amorphous material has been observed in SAFOD as well as TCDP samples. In line with previous publications, we propose that melt, observed in TCDP black gouge samples, was produced by seismic slip (melt origin) whereas amorphous material in SAFOD samples was formed by comminution of grains (crush origin) rather than by melting. Dauphiné twins in quartz grains of SAFOD and TCDP samples may indicate high seismic stress. The differences in the crystallographic preferred orientation of calcite between SAFOD and TCDP samples are significant. Microstructures resulting from dissolution–precipitation processes were observed in both faults but are more frequently found in SAFOD samples than in TCDPmore » fault rocks. As already described for many other fault zones clay-gouge fabrics are quite weak in SAFOD and TCDP samples. Clay-clast aggregates (CCAs), proposed to indicate frictional heating and thermal pressurization, occur in material taken from the PSZ of the Chelungpu Fault, as well as within and outside of the SAFOD deforming zones, indicating that these microstructures were formed over a wide range of slip rates.« less

Authors:
; ; ; ; ; ; ;  [1];  [2];  [2]
  1. UCB
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
NSFFOREIGNDOE - BASIC ENERGY SCIENCES
OSTI Identifier:
1132114
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Struct. Geol.; Journal Volume: 65; Journal Issue: 08, 2014
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Janssen, C., Wirth, R., Wenk, H. -R., Morales, L., Naumann, R., Kienast, M., Song, S. -R., Dresen, G., GFZ), and NTU). Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples. United States: N. p., 2014. Web. doi:10.1016/j.jsg.2014.04.004.
Janssen, C., Wirth, R., Wenk, H. -R., Morales, L., Naumann, R., Kienast, M., Song, S. -R., Dresen, G., GFZ), & NTU). Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples. United States. doi:10.1016/j.jsg.2014.04.004.
Janssen, C., Wirth, R., Wenk, H. -R., Morales, L., Naumann, R., Kienast, M., Song, S. -R., Dresen, G., GFZ), and NTU). Wed . "Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples". United States. doi:10.1016/j.jsg.2014.04.004.
@article{osti_1132114,
title = {Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples},
author = {Janssen, C. and Wirth, R. and Wenk, H. -R. and Morales, L. and Naumann, R. and Kienast, M. and Song, S. -R. and Dresen, G. and GFZ) and NTU)},
abstractNote = {The microstructures, mineralogy and chemistry of representative samples collected from the cores of the San Andreas Fault drill hole (SAFOD) and the Taiwan Chelungpu-Fault Drilling project (TCDP) have been studied using optical microscopy, TEM, SEM, XRD and XRF analyses. SAFOD samples provide a transect across undeformed host rock, the fault damage zone and currently active deforming zones of the San Andreas Fault. TCDP samples are retrieved from the principal slip zone (PSZ) and from the surrounding damage zone of the Chelungpu Fault. Substantial differences exist in the clay mineralogy of SAFOD and TCDP fault gouge samples. Amorphous material has been observed in SAFOD as well as TCDP samples. In line with previous publications, we propose that melt, observed in TCDP black gouge samples, was produced by seismic slip (melt origin) whereas amorphous material in SAFOD samples was formed by comminution of grains (crush origin) rather than by melting. Dauphiné twins in quartz grains of SAFOD and TCDP samples may indicate high seismic stress. The differences in the crystallographic preferred orientation of calcite between SAFOD and TCDP samples are significant. Microstructures resulting from dissolution–precipitation processes were observed in both faults but are more frequently found in SAFOD samples than in TCDP fault rocks. As already described for many other fault zones clay-gouge fabrics are quite weak in SAFOD and TCDP samples. Clay-clast aggregates (CCAs), proposed to indicate frictional heating and thermal pressurization, occur in material taken from the PSZ of the Chelungpu Fault, as well as within and outside of the SAFOD deforming zones, indicating that these microstructures were formed over a wide range of slip rates.},
doi = {10.1016/j.jsg.2014.04.004},
journal = {J. Struct. Geol.},
number = 08, 2014,
volume = 65,
place = {United States},
year = {Wed Aug 20 00:00:00 EDT 2014},
month = {Wed Aug 20 00:00:00 EDT 2014}
}