Faults (shear zones) in the Earth's mantle
Faults (shear zones) in the Earth's mantle
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DOI：
10.1016/j.tecto.2012.06.006
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发表时间：
2012-08
期刊：
影响因子：
2.9
通讯作者：
A. Vauchez;A. Tommasi;D. Mainprice
中科院分区：
文献类型：
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作者：
A. Vauchez;A. Tommasi;D. Mainprice
大地测量数据支持位于岩石圈块边界断层中的短期大陆变形。在地表观察到的主要“断层”是否影响岩石圈地幔，如果影响的话，应变如何分布是理解岩石圈板块力学行为的主要问题。从造山地块中变形橄榄岩、蛇绿岩和地幔捕虏体的直接观察到主要断层带下方的地震反射体和地震各向异性，各种证据一致支持主要断层延伸到岩石圈地幔中。这篇综述强调，尽管人们对岩石圈地幔变形的许多方面仍然知之甚少。解释震后变形需要最上地壳摩擦断层的变形与韧性地壳和地幔的局部剪切之间的耦合，但只有当浅层岩石圈地幔温度较高（莫霍面> 800°C）时，从大地测量数据推导出来并从实验室实验推断出的地幔粘度才能得到调和。地震各向异性，特别是剪切波分裂，为主要横流断层下方岩石圈地幔数十公里宽区域的相干变形提供了强有力的证据。然而它无法检测狭窄的应变局部化区域或浅倾断层。地震剖面成像岩石圈地幔中的浅倾地震反射体，被解释为地幔中正断层或较少出现的逆断层的延续。然而，人们对这些反射器的性质知之甚少。研究变形过程的尺度（由于地球表面连续地幔暴露的尺寸有限，最多几公里）与通过地球物理观测推断地幔应变局部化的尺度（几十公里）存在很大差异。尽管如此，将自然变形橄榄岩中的变形微观结构和晶体择优取向的数据与地震观测相结合，仍然可以讨论可能在地幔剪切带的发育中发挥作用的应变局部化过程。
Geodetic data support a short-term continental deformation localized in faults bounding lithospheric blocks. Whether major “faults” observed at the surface affect the lithospheric mantle and, if so, how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates. A variety of evidence, from direct observations of deformed peridotites in orogenic massifs, ophiolites, and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones, consistently supports prolongation of major faults into the lithospheric mantle. This review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood. Coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post-seismic deformation, but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high (>800°C at the Moho). Seismic anisotropy, especially shear wave splitting, provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults. Yet it cannot detect narrow strain localization zones or shallowly dipping faults. Seismic profiling images shallow-dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or, less frequently, inverse faults in the mantle. However the nature of these reflectors is poorly understood. There is a large discrepancy between the scale at which deformation processes are studied (a few kilometers, at most, due to the limited size of continuous mantle exposures at the Earth's surface) and the scale inferred for strain localization in the mantle from geophysical observations (tens of kilometers). Combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones.