Oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges
Oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges
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DOI：
10.1016/j.epsl.2009.09.020
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发表时间：
2009-10
影响因子：
5.3
通讯作者：
M. Cannat;D. Sauter;J. Escartín;L. Lavier;S. Picazo
中科院分区：
文献类型：
--
作者：
M. Cannat;D. Sauter;J. Escartín;L. Lavier;S. Picazo
本文分析了西南印度海脊东部轴向滑脱断裂下盘26年来形成的39个波纹面的地形特征和重力特征。这些波纹表面似乎是在熔体供应量约为全球大洋中脊平均熔体供应量的一半时形成的，我们发现，它们目前相对于邻近的非波纹海底的隆起地形大多是在其形成的末期，即“终止阶段”获得的。这一构型也是其他海洋中许多离轴波纹表面的特征，表明在波纹表面形成期间，板块的弯曲刚性很低，在终止阶段显著增加。在Buck(1988)之后，我们假设与板块弯曲有关的应力会导致断层下盘的内部变形和破坏，这与软化有关。作为波纹面形成时加强底板弱化的一种可能机制，我们提出在辉长岩侵入岩附近的地幔超镁铁岩中形成覆盖有滑石、角闪石、绿泥石和蛇纹石等含水矿物的弱剪切带。如果这一假设是正确的，则在缓慢扩张的山脊上沿轴向拆离断层的底盘弱化和翻转的量可能既受拆离下盘中热液的获取，也受出土超镁岩中辉长岩侵入体的丰度和分布的控制。
We analyse the topography and gravity signature of 39 corrugated surfaces formed over the past 26myrs in the footwall of axial detachment faults at the eastern Southwest Indian Ridge. These corrugated surfaces appear to have formed at a melt supply about half the global melt supply average for mid-ocean ridges, and we find that their presently elevated topography, relative to adjacent non-corrugated seafloor, was mostly acquired at the end of their formation, at the “termination stage”. This configuration, which also characterizes many off-axis corrugated surfaces in other oceans, suggests that the plate flexural rigidity was very low during the formation of the corrugated surface, and increased significantly at the termination stage. Following Buck (1988), we hypothesize that stresses related to bending of the plate cause internal deformation and damage in the footwall of the fault, which is associated with weakening. As a possible mechanism for enhanced footwall weakening while corrugated surfaces form, we propose the formation of weak shear zones coated with hydrous minerals such as talc, amphibole, chlorite and serpentine, in mantle-derived ultramafics next to gabbro intrusions. If this hypothesis is correct, the amount of footwall weakening and roll-over along axial detachment faults at slow spreading ridges may be controlled both by access to hydrothermal fluids in the footwall of the detachment, and by the abundance and distribution of gabbros intrusions in exhumed ultramafics.