Thin pseudotachylytes in faults of the Mt. Abbot quadrangle, Sierra Nevada: Physical constraints for small seismic slip events
Thin pseudotachylytes in faults of the Mt. Abbot quadrangle, Sierra Nevada: Physical constraints for small seismic slip events
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DOI：
10.1016/j.jsg.2008.05.003
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发表时间：
2008-01-01
影响因子：
3.1
通讯作者：
Pollard, David D.
中科院分区：
文献类型：
--
作者：
Griffith, W. Ashley;Di Toro, Giulio;Pollard, David D.
我们的文件发生的假玄武玻璃（凝固熔体产生的地震滑动）沿着走滑断层在爱迪生湖花岗闪长岩的山。Abbot quadrangle，Sierra内华达州，加州，并提供地震断层作用期间对环境条件的约束。假玄武玻璃的厚度小于0.3毫米，通常在厚度达1厘米的断层中发现。沿沿着采样断层测得的总左偏约为20 cm。现场和显微构造证据表明，断层利用了预先存在的矿化节理，并显示出以下叠加结构（推断环境温度）：糜棱岩或多或少与石英脉（> 400摄氏度），碎裂岩和假玄武质岩（类似于250摄氏度）或多或少与绿帘石脉和沸石脉（< 200摄氏度）同时代。根据对断层显微结构的观察，结合理论传热和能量收支计算，我们认为，只有一小部分（< 30%）的总偏移量与地震滑动（即假玄武玻璃）有关。在亚毫米厚的区域中假玄武玻璃的存在支持了地震滑动过程中极端剪切局部化的概念。这些假玄武玻璃的难以捉摸的性质表明，在露头和光学显微镜的观察是不足以排除摩擦熔融的地震滑动的结果，在类似的断层岩。(C)2008爱思唯尔有限公司保留所有权利。
We document the occurrence of pseudotachylyte (solidified melt produced during seismic slip) along strike-slip faults in the Lake Edison granodiorite of the Mt. Abbot quadrangle, Sierra Nevada, California and provide constraints on ambient conditions during seismic faulting. The pseudotachylytes are less than 0.3 mm thick and are found in faults typically up to 1 cm in thickness. Total measured left-lateral offset along sampled faults is approximately 20 cm. Field and microstructural evidence indicate that the faults exploited pre-existing mineralized joints and show the following overprinting structures (with inferred ambient temperatures): mylonites are more or less coeval with quartz veins (> 400 degrees C), cataclasites and pseudotachylytes (similar to 250 degrees C) more or less coeval with epidote veins, and zeolite veins (< 200 degrees C). Based on observations of the microstructural textures of faults combined with theoretical heat transfer and energy budget calculations, we suggest that only a fraction (< 30%) of the total offset was associated with seismic slip (i.e. pseudotachylyte). The presence of pseudotachylyte in sub-millimeter thick zones lends support for the concept of extreme shear localization during seismic slip. The elusive nature of these pseudotachylytes demonstrates that observations in outcrop and optical microscope are not sufficient to rule out frictional melting as a consequence of seismic slip in similar fault rocks. (C) 2008 Elsevier Ltd. All rights reserved.