The structure, evolution and symmetry of the magma-poor rifted margins of the North and Central Atlantic: A synthesis
The structure, evolution and symmetry of the magma-poor rifted margins of the North and Central Atlantic: A synthesis
复制标题
DOI：
10.1016/j.tecto.2008.09.002
复制
发表时间：
2009-04
期刊：
影响因子：
2.9
通讯作者：
T. Reston
中科院分区：
文献类型：
--
作者：
T. Reston
缺乏岩浆的裂陷边缘一贯表现出极端的地壳减薄，伴随着正断层作用，地壳下地幔的蛇纹化作用减薄到小于8±2 km，以及大陆-海洋过渡带内地幔的大面积去顶，伴随着拆离和其他大偏移断层的发展。这些观察结果是冷岩石圈逐渐延伸远离热异常（例如羽流）的逻辑结果。虽然岩浆活动的缺乏可以解释的深度依赖的岩石圈的延伸，并通过预耗尽的地壳下岩石圈，裂谷以上最初冷的岩石圈下地幔也可以解释在某些边缘观察到的沉降赤字：同步裂谷沉降缓冲的同时流入温暖的海洋软流圈。随着莫霍面的延伸、变薄和冷却，中地壳和深部的韧性蠕动层变得越来越脆，导致上地壳和下地壳之间的耦合增加，最终整个地壳变脆，断层从表面穿过莫霍面，将水带入地幔并导致其蛇纹石化。耦合的增加和蛇纹岩的发育预示着一旦整个地壳变脆，后期不对称性的发展。这样的determinants成像在一些边缘和推断的其他人;分析的地壳结构共轭边缘表明，这些是近似对称的，直到这个晚期阶段，当他们变得明显不对称。类似的分析表明，地壳的深度依赖性拉伸不足以解释沿着断层的可见伸展量与地壳减薄量之间的差异。相反，这种“伸展差异”可能与脆性变形的复杂演化有关，通过多个阶段和样式的断裂，与岩石圈的流变学性质和强度的变化，因为它是减薄。复杂的多期断层在地壳完全分离后继续存在，导致橄榄岩基底的大面积折返，其顶部到处都有折返的滑动面，类似于在洋中脊观察到的波纹面。地幔去顶和海底扩张过程的相似性使得COT和真正的洋壳之间的区别变得困难，甚至可能没有实际意义。
Magma-poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting, the serpentinization of the mantle beneath crust thinned to less than 8±2 km, and the unroofing of a broad zone of mantle within the continent–ocean transition, accompanied by the development of detachment and other large-offset faults. These observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes. Although the paucity of magmatism may be explained by depth-dependent extension of the lithosphere, and by pre-depleted sub-crustal lithosphere, rifting above initially cool sub-lithospheric mantle also may explain the subsidence deficit observed at some margins: synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere. As it extends, thins and cools, ductile creeping layers in the mid- and deep crust become progressively more brittle, resulting in increased coupling between the upper and lower crust, and eventually the embrittlement of the entire crust, faults cutting from the surface across the Moho, bringing water into the mantle and causing its serpentinization. Increased coupling and the development of serpentine detachments predict the development of late-stage asymmetry once the entire crust is brittle. Such detachments are imaged on some margins and inferred on others; analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric. Similar analyses show that depth-dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning. Instead this “extension discrepancy” may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting, related to the changes in the rheological character and strength of the lithosphere as it is thinned. Complex polyphase faulting continues after complete crustal separation, resulting in the exhumation of broad expanses of peridotitic basement, the top of which is everywhere marked by an exhumed slip surface, similar to the corrugated surface observed at mid-ocean ridges. The similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the COT and true oceanic crust difficult and possibly moot.