The Rheological Evolution of Brittle‐Ductile Transition Rocks During the Earthquake Cycle: Evidence for a Ductile Precursor to Pseudotachylyte in an Extensional Fault System, South Mountains, Arizona
The Rheological Evolution of Brittle‐Ductile Transition Rocks During the Earthquake Cycle: Evidence for a Ductile Precursor to Pseudotachylyte in an Extensional Fault System, South Mountains, Arizona
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地震周期期间脆性-韧性过渡岩石的流变演化：亚利桑那州南山伸展断层系统中的韧性前体到假速晶石的证据
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
E. Miranda
中科院分区：
文献类型：
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作者：
Craig Stewart;E. Miranda
我们研究了脆韧性转换(BDT)下剪切带岩石的流变演化如何受到与地震活动有关的同时代韧性剪切和假玄武岩发育的影响。我们重点研究了南山核杂岩的下盘围岩，并利用电子背散射衍射(EBSD)分析了花岗闪长糜棱岩在BDT之下假玄武岩发育之前和过程中应变的局部化。在假玄武岩所寄生的糜棱岩中，变形被分割成石英，其中石英表现出结晶择优的取向模式和指示位错蠕变过程中动态再结晶的微观结构。动态再结晶过程中晶粒尺寸的减小导致了由流体辅助的晶粒度敏感蠕变(GSS)调节的晶界滑移(GBS)的开始，在假黄晶发育之前，应变在富石英层中局部化。寄主糜棱岩中GBS的面理平行带和多晶石英残存碎屑中的GBS特征表明，GBS带是原地假黄长岩产生的韧性前兆。在假玄武岩的发育过程中，应变被分割成熔融相，残存碎屑中的GSS变形继续，直到熔体的结晶阻碍流动，导致其他GBS带的假玄武岩的发育。我们将具有韧性前兆的同时代假玄武岩解释为BDT附近地震事件的证据。粒度测压结果表明，寄主糜棱岩(~160 Mpa)和假玄武岩残存碎屑(~200 Mpa)中均存在较高的差应力，这分别与地震旋回的震间和同震阶段的高应力一致。
We investigate how the rheological evolution of shear zone rocks from beneath the brittle‐ductile transition (BDT) is affected by coeval ductile shear and pseudotachylyte development associated with seismicity during the earthquake cycle. We focus our study on footwall rocks of the South Mountains core complex, and we use electron backscatter diffraction (EBSD) analyses to examine how strain is localized in granodiorite mylonites both prior to and during pseudotachylyte development beneath the BDT. In mylonites that are host to pseudotachylytes, deformation is partitioned into quartz, where quartz exhibits crystallographic‐preferred orientation patterns and microstructures indicative of dynamic recrystallization during dislocation creep. Grain size reduction during dynamic recrystallization led to the onset of grain boundary sliding (GBS) accommodated by fluid‐assisted grain size‐sensitive (GSS) creep, localizing strain in quartz‐rich layers prior to pseudotachylyte development. The foliation‐parallel zones of GBS in the host mylonites, and the presence of GBS traits in polycrystalline quartz survivor clasts indicate that GBS zones were the ductile precursors to in situ pseudotachylyte generation. During pseudotachylyte development, strain was partitioned into the melt phase, and GSS deformation in the survivor clasts continued until crystallization of melt impeded flow, inducing pseudotachylyte development in other GBS zones. We interpret the coeval pseudotachylytes with ductile precursors as evidence of seismic events near the BDT. Grain size piezometry yields high differential stresses in both host mylonites (~160 MPa) and pseudotachylyte survivor clasts (> ~200 MPa), consistent with high stresses during interseismic and coseismic phases of the earthquake cycle, respectively.
含白云母石英岩中的假速晶石：同震摩擦引起的石英熔化和塑性变形
影响因子：
3.1
作者：
Bestmann;Pennacchioni;Göken;de Wall
通讯作者：
de Wall