The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust
The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust
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DOI：
10.1029/2018jb016461
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发表时间：
2019-08-01
影响因子：
3.9
通讯作者：
Renard, Francois
中科院分区：
文献类型：
--
作者：
Jamtveit, Bjorn;Petley-Ragan, Arianne;Renard, Francois
岩石流变学和密度对岩石圈在板块边界对板块构造力的响应具有一级效应。这些岩石性质的变化是由变质转化过程控制的，而变质转化过程又严重依赖于流体的存在。在大陆碰撞开始时，下地壳在大多数情况下是干燥和坚固的。然而，如果暴露于内部产生或外部供应的流体，增厚的地壳将发生反应，并通过流体驱动的变质反应转化为机械强度较弱的岩性。流体的引入往往与地壳深部地震有关。显微构造证据表明，在强的高应力岩石中，地震滑动可能是由脆性变形引起的，动态破裂引起的围岩破坏在允许流体进入与干燥和高活性下地壳岩石接触方面起着非常重要的作用。由此产生的变质作用产生较弱的岩石，随后通过粘性蠕变变形。强岩石的高应力环境中包含的大量弱岩石可能会经历向更高压力的显着偏移，而没有任何相关的埋藏。在速度强化状态下，缓慢和高度局部化的蠕变过程可能会沿断层产生沿着糜棱岩剪切带，这些剪切带最初的特征是地震引起的摩擦熔化和围岩破坏。然而，应力脉冲从地震在较浅的脆性制度可能踢开始新的地震滑动在速度减弱条件。这些过程表明，在大陆碰撞过程中，下地壳的演化是由脆性变形，流体-岩石相互作用和蠕变流动之间的瞬态相互作用控制的。
Rock rheology and density have first-order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid-driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall-rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake-generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid-rock interactions, and creep flow.