Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds |
| |
| Institution: | 1. Department of Geosciences, University of Padova, Via Gradenigo 6, I-35131 Padova, Italy;2. School of Geography, Earth and Environmental Sciences, Plymouth University, United Kingdom;3. GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany;1. GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Schlossgarten 5, 91054 Erlangen, Germany;2. Dipartimento di Geoscienze, Università di Padova, Via G. Gradenigo 6, 35131 Padova, Italy |
| |
| 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 μm) aggregates along microshear zones (50–150 μm 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 μm) 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. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
