Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds
Deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte-bearing brittle faults: A matter of a few seconds
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DOI：
10.1016/j.jsg.2011.10.001
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发表时间：
2012-05-01
影响因子：
3.1
通讯作者：
de Wall, H.
中科院分区：
文献类型：
--
作者：
Bestmann, M.;Pennacchioni, G.;de Wall, H.
构造伪岩，即淬灭的摩擦引起的硅酸盐熔体，记录了沿断层的同震滑动，主要来自与碎裂岩相关的脆性地壳。在本研究中，我们记录了石英沿微剪切带（50-150 μ m厚）在靠近石英岩（东阿尔卑斯Schneeberg正断裂带）和石英（南阿尔卑斯Adamello断裂带）的两个不同断层的假石质附近的主岩中出现超细晶（粒度为1-2 μ m）团聚体的再结晶。从主石英到微剪切带内部的转变包括：(1)形成高位错密度；（ii）细小（0.3-0.5 μ m）多角化到亚晶粒，由无序到有序的位错壁定义；（iii）无位错的新晶粒的马赛克聚集体的发展。石英向微剪切带的晶体优先取向（CPO）表现出由主晶通过亚晶旋转再结晶向可能与晶界滑动有关的近乎随机的CPO的渐进错取向。这些超细聚集体在自然界中似乎通常与假羟基酸盐有关。我们认为，石英晶体塑性变形伴随着晶粒尺寸的急剧细化是由于摩擦加热引起的高差应力和温度瞬变引起的断层滑动的同震阶段。在地震破裂传播阶段和断层滑动的最初阶段，形成了位于前兆断裂上的微剪切带。热模型表明，包括恢复过程在内的再结晶过程发生在几十秒的时间间隔内。(C) 2011 Elsevier Ltd.版权所有。
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.