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

Bestmann M, Pennacchioni G, Nielsen S, Göken M, de Wall H (2012)

Publication Type: Journal article, Original article

Publication year: 2012

Journal

Journal of Structural Geology Elsevier

Book Volume: 38

Pages Range: 21-38

DOI: 10.1016/j.jsg.2011.10.001

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.

Authors with CRIS profile

Michael Bestmann Professur für Tektonik Mathias Göken Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften) Helga de Wall Professur für Tektonik

Additional Organisation(s)

Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)

Involved external institutions

University of Padua / Universita degli Studi di Padova IT Italy (IT) Istituto Nazionale di Geofisica e Vulcanologia (INGV) IT Italy (IT)

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.

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