Collaborative Research: Experimental Study of the Origin and Nature of High Pressure Faulting Relevant to Earthquakes in Subducting Lithosphere

Green 粤ICP备050125938号 常规的脆性破坏在地球内部的重要深度是不可能的，因为压力和温度的组合确保了岩石的流动强度在断裂强度之前被超过。 然而，地震大量发生在俯冲带的海洋岩石圈下降板块内，在一些情况下，深度高达680公里，在那里它们突然停止。 虽然这些地震发生的机制尚不清楚，但它们的地震信号表明，它们代表了沿着断层的岩石突然破裂。 目前已知有两种机制可以使断层在高压下发生。 第一，脱水脆化，涉及含水矿物的分解产生的自由流体相;自由流体有助于微裂纹的打开，这是导致剪切破坏的关键步骤。 就目前所知，如果地幔中存在适当的含水相，并且它们的稳定场在适当的条件下发生变化，从而产生所观察到的深度分布，则这种机制可能解释所有的地震。第二，相变诱发断层可以触发橄榄石的相变过程中，其密度的多晶型物，发生随着深度的增加。 这种机制可以潜在地解释双峰深度分布的地震和他们突然终止在上地幔的基础上，如果亚稳橄榄石是保存在俯冲带的冷核在过渡带深度。 然而，鉴于目前对俯冲岩石圈内相位分布的理解，这两种机制都不能很好地解释深度超过500公里的特大地震的发生。研究人员将运用他们在高压技术、实验变形和地震学方面的集体专业知识，实现以下目标：（1）检验含水断层复活的假设;（2）通过声发射的检测和定位，监测脱水脆化和变形诱发断层的实验;（3）为剪切破坏的现场同步加速器实验开发改进的高压实验组件设计;（4）利用脱水脆化和相变诱发断裂实验，对这两种断裂机制提出新的约束。

Green EAR-0125938 Conventional brittle failure is impossible at significant depth within Earth because the combination of pressure and temperature ensures that the flow strength of rocks is exceeded before the fracture strength. Nevertheless, earthquakes occur abundantly within descending slabs of oceanic lithosphere in subduction zones, in several cases to depths as great as 680 km, where they stop abruptly. Although the mechanism by which these earthquakes occur is unknown, their seismic signals ensure that they represent sudden failure of rock along a fault. There are two mechanisms presently known that can enable faulting to occur at high pressure. The first, dehydration embrittlement, involves generation of a free fluid phase by breakdown of hydrous minerals; the free fluid assists in opening of microcracks which is a crucial step leading to shear failure. So far as is known, this mechanism could potentially explain all earthquakes if appropriate hydrous phases are present in the mantle and if their stability fields are such that they dehydrate under appropriate conditions to yield the observed depth distribution. The second, phase-transformation-induced faulting can be triggered during the phase transformations of olivine to its denser polymorphs, which occur with increasing depth. This mechanism can potentially explain the bimodal depth distribution of earthquakes and their abrupt termination at the base of the upper mantle if metastable olivine is preserved in the cold cores of subduction zones at transition-zone depths. However, given current understanding of the phase distribution within subducting lithosphere, neither mechanism can comfortably explain the occurrence of very large earthquakes at depths exceeding 500 km. The investigators will apply their collective expertise in high-pressure technology, experimental deformation, and seismology to achieve the following: (1) test the hypothesis of reactivation of hydrated faults; (2) monitor experiments on dehydration embrittlement and transformation-induced faulting by detection and location of acoustic emissions; (3) develop improved high-pressure experimental assembly designs for in situ synchrotron experiments on shear failure; (4) use faulting experiments on both dehydration embrittlement and phase-transformation-induced faulting to place new constraints on these two faulting mechanisms.