Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds

Journal article
(Original article)


Publication Details

Author(s): Bestmann M, Pennacchioni G, Nielsen S, Göken M, de Wall H
Journal: Journal of Structural Geology
Publication year: 2012
Volume: 38
Pages range: 21-38
ISSN: 0191-8141


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.



FAU Authors / FAU Editors

Bestmann, Michel Dr.
Professur für Geologie unter besonderer Berücksichtigung der Strukturgeologie [Tektonik] und Photogeologie
de Wall, Helga Prof. Dr.
Professur für Geologie unter besonderer Berücksichtigung der Strukturgeologie [Tektonik] und Photogeologie
Göken, Mathias Prof. Dr.
Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)


External institutions
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
University of Padua


How to cite

APA:
Bestmann, M., Pennacchioni, G., Nielsen, S., Göken, M., & de Wall, H. (2012). Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds. Journal of Structural Geology, 38, 21-38. https://dx.doi.org/10.1016/j.jsg.2011.10.001

MLA:
Bestmann, Michel, et al. "Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds." Journal of Structural Geology 38 (2012): 21-38.

BibTeX: 

Last updated on 2018-11-08 at 01:14