Fragmentation of wall rock garnets during deep crustal earthquakes.
Fragmentation of wall rock garnets during deep crustal earthquakes.
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DOI：
10.1126/sciadv.1602067
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发表时间：
2017-02
期刊：
影响因子：
13.6
通讯作者：
Jamtveit B
中科院分区：
文献类型：
--
作者：
Austrheim H;Dunkel KG;Plümper O;Ildefonse B;Liu Y;Jamtveit B
深部地壳地震造成围岩破碎。断裂和断层在所有尺度上都是地壳的谜，与之相关的变形被认为对地壳的岩石学和结构演化产生了重大影响。然而，尽管有丰富的直接可观察到的地震活动，明确的证据，地震滑动率沿沿着古老的断层是罕见的，通常与摩擦熔融和形成的假玄武玻璃。我们报告的新的微观结构，从石榴石晶体在地震滑动面附近，横切下地壳麻粒岩在中深地震在卑尔根弧区，挪威西部，约4.2亿年前。地震荷载引起围岩石榴石大量位错形成和破碎。微破裂和硫化物熔体的注入发生在加载的早期阶段。随后的膨胀导致流体沿着沿着微裂缝、位错、亚晶粒和晶粒边界的网络普遍输送到石榴石中，导致在破碎的石榴石内部生长出丰富的矿物包裹体。晶界迁移的再结晶作用封闭了地震事件产生的大部分孔隙和裂缝。这种围岩蚀变代表了地震引发的变质转变过程的初始阶段，最终导致了区域范围内下地壳的改造。
Deep crustal earthquakes cause fragmentation of wall rocks. Fractures and faults riddle the Earth’s crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. Seismic loading caused massive dislocation formations and fragmentation of wall rock garnets. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. This wall rock alteration represents the initial stages of an earthquake-triggered metamorphic transformation process that ultimately led to reworking of the lower crust on a regional scale.