Life cycle of oceanic core complexes
Life cycle of oceanic core complexes
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DOI：
10.1016/j.epsl.2009.08.016
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发表时间：
2009-10-15
影响因子：
5.3
通讯作者：
Harris, M.
中科院分区：
文献类型：
--
作者：
MacLeod, C. J.;Searle, R. C.;Harris, M.
洋核杂岩是非常大偏移量的低角度正断层的隆起下盘，这些断层在缓慢扩张的海脊处将下地壳和地幔岩石挖出到海底。虽然它是建议的基础上的数值模拟，他们形成的岩浆供应相对减少的时期，很少有人知道他们如何启动和变得不活跃，也不知道为什么只有某些正常的断层系统发展成核心复杂。在本文中，我们提出了近底侧扫声纳/测深剖面仪调查和采样研究的中大西洋海脊近13度N，确定关键控制大洋核心复杂的发展和演变的结果。我们发现，核心复杂的剥离断层开始作为高角度（65度+/- 10度）的正断层没有什么不同，从周围的谷壁断层，并像他们一样，迅速变平的倾角类似于30度的弯曲卸载的反应，但是，在某些结构滑动继续，而不是被中继向内到一个新的正断层。失控位移似乎主要是由当地减弱的岩浆供应低于临界阈值，然后由应变本地化海水渗透和滑石形成沿着断层带的帮助。当核杂岩活跃，火山活动被抑制或不存在时，扩张变得明显不对称。当这种不对称性达到一定程度时，板块的分离量超过板块分离总量的一半，活动断层就会穿过轴向谷迁移。因此，岩浆侵位和捕获的剥离断层的下盘，而不是被注入到上盘，解释了辉长岩体和其他熔融残留物在海洋核杂岩的频繁存在。当有足够的岩浆侵位到足以淹没拆离断层时，核杂岩最终终止;在北纬13度区域，新火山脊从沿着走向的岩浆坚固段横向传播穿过它们。(C)2009 Elsevier B. V.保留所有权利。
Oceanic core complexes are the uplifted footwalls of very-large-offset low-angle normal faults that exhume lower crust and mantle rocks onto the seafloor at slow-spreading ridges. Although it is suggested on the basis of numerical modelling that they form during periods of relatively reduced magma supply, little is known about how they initiate and become inactive, nor why only certain normal fault systems develop into core complexes. In this paper we present results from a near-bottom sidescan sonar/bathymetric profiler survey and sampling study of the Mid-Atlantic Ridge near 13 degrees N that identify the critical controls on oceanic core complex development and evolution. We show that core complex detachment faults initiate as high-angle (65 degrees +/- 10 degrees) normal faults no different from surrounding valley-wall faults and, like them, rapidly flatten to dips of similar to 30 degrees in response to flexural unloading; however, on certain structures slip continues rather than being relayed inward onto a new normal fault. Runaway displacement appears to be triggered primarily by local waning of magma supply below a critical threshold, then aided by strain localisation resulting from seawater penetration and talc formation along the fault zones. Spreading becomes markedly asymmetric when the core complexes are active, and volcanism is suppressed or absent. When the asymmetry is such that the detachments accommodate more than half the total plate separation the active faults migrate across the axial valley. As a consequence magma is emplaced into and captured by the footwall of the detachment fault rather than being injected into the hanging wall, explaining the frequent presence of gabbro bodies and other melt relicts at oceanic core complexes. Core complexes are ultimately terminated when sufficient magma is emplaced to overwhelm the detachment fault; in the 13 degrees N area by neovolcanic ridges propagating laterally across them from magmatically robust segments along strike. (C) 2009 Elsevier B.V. All rights reserved.