Please use this identifier to cite or link to this item:
Authors: Bestmann, M.* 
Pennacchioni, G.* 
Nielsen, S.* 
Goeken, M.* 
de Wall, H.* 
Title: Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds
Issue Date: 2012
Series/Report no.: /38(2012)
DOI: 10.1016/j.jsg.2011.10.001
Keywords: friction
seismic fault
Subject Classification04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution 
Abstract: Tectonic pseudotachylytes, i.e. quenched friction-induced silicate melts, record coseismic slip along faults and are mainly reported from the brittle crust in association with cataclasites. In this study, we document the occurrence of recrystallization of quartz to ultrafine-grained (grain size 1-2 mu m) aggregates along microshear zones (50-150 mu m thick) in the host rock adjacent to pseudotachylytes from two different faults within quartzite (Schneeberg Normal Fault Zone, Eastern Alps), and tonalite (Adamello fault, Southern Alps) in the brittle crust. The transition from the host quartz to microshear zone interior includes: (i) formation of high dislocation densities; (ii) fine (0.3-0.5 mu m) polygonization to subgrains defined by disordered to well-ordered dislocation walls; (iii) development of a mosaic aggregate of dislocation-free new grains. The crystallographic preferred orientation (CPO) of quartz towards the microshear zone shows a progressive misorientation from the host grain, by subgrain rotation recrystallization, to a nearly random CPO possibly related to grain boundary sliding. These ultrafine aggregates appear to be typically associated with pseudotachylytes in nature. We refer the crystal plastic deformation of quartz accompanied by dramatic grain size refinement to the coseismic stages of fault slip due to high differential stress and temperature transients induced by frictional heating. Microshear zones localized on precursory fractures developed during the stages of earthquake rupture propagation and the very initial stages of fault slip. Thermal models indicate that the process of recrystallization, including recovery processes, occurred in a time lapse of a few tens of seconds. (C) 2011 Elsevier Ltd. All rights reserved.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Bestmann2012.pdfMain article5.48 MBAdobe PDFView/Open
Show full item record

Page view(s)

Last Week
Last month
checked on Aug 15, 2018


checked on Aug 15, 2018

Google ScholarTM