Metamorphic core complexes: windows into the mechanics and rheology of the crust
Metamorphic core complexes: windows into the mechanics and rheology of the crust
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DOI：
10.1144/jgs2014-036
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发表时间：
2014-11
影响因子：
2.7
通讯作者：
J. Platt;W. Behr;F. Cooper
中科院分区：
文献类型：
--
作者：
J. Platt;W. Behr;F. Cooper
变质核杂岩是正断层位移的产物，这种位移足以使岩石从脆 - 韧性转换带以下被抬升出露。这些断层（滑脱断层）可能在脆性地壳内以陡角开始形成，但它们会延伸到韧性的中地壳，并且在位移过程中由于上盘伸展而旋转至较缓的倾角。由于挠曲均衡再调整，出露的下盘通常呈现拱形或穹形几何形状，并且可能被在滑脱断层缓倾、低摩擦的浅部地段滑动的强烈伸展的上地壳岩石所覆盖。在滑脱断层之下出露的变质岩记录了随着温度降低，流动应力、应变局部化和应变率逐渐增加的情况，为了解中地壳的物理条件和变形过程提供了一个窗口。下盘岩石的变质和变形历史除了反映伴随抬升出露的过程外，还可能反映在滑脱断层形成之前的构造过程。这些过程可能包括片麻岩穹隆的底辟侵位，或者在俯冲通道中的抬升出露，并且可能与核杂岩的形成没有直接关系。有利于核杂岩形成的因素包括伸展地壳的高重力势能、软弱的流变学性质以及构造边界条件的改变，比如板块汇聚的停止或减缓。
Metamorphic core complexes are products of normal-fault displacements sufficient to exhume rocks from below the brittle–ductile transition. These faults (detachments) may initiate within the brittle crust at steep angles, but they sole into the ductile middle crust, and during displacement rotate to gentler dips due to hanging-wall extension. The exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment, and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping, low-friction shallow segments of the detachment. Metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress, strain localization and strain-rate with decreasing temperature, providing a window into physical conditions and deformational processes in the mid-crust. The metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault, in addition to those accompanying exhumation. These processes may include diapiric emplacement of gneiss domes, or exhumation in a subduction channel, and may not be directly related to formation of the core complex. Factors favouring core complex formation are high gravitational potential energy of the extending crust, weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence.