Seismic structure of Cocos and Malpelo Volcanic Ridges and implications for hot spot‐ridge interaction
Seismic structure of Cocos and Malpelo Volcanic Ridges and implications for hot spot‐ridge interaction
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科科斯和马尔佩洛火山脊的地震结构及其对热点-山脊相互作用的影响
DOI：
10.1029/2003jb002431
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发表时间：
2003
影响因子：
--
通讯作者：
J. Bialas
中科院分区：
文献类型：
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作者：
V. Sallarés;P. Charvis;E. Flueh;J. Bialas
[1]科科斯和马尔佩洛火山脊是增厚的海洋地壳块，被认为是过去2000万年期间加拉帕戈斯热点和科科斯-纳斯卡扩散中心之间相互作用的结果。在这项工作中，我们调查的地震结构，这两个海岭沿着三个广角断面在巴拿马盆地和加拉帕戈斯羽-新调查板内岩浆（PAGANINI）-1999年的实验。一个二维的速度场与莫霍几何得到联合折射/反射走时层析成像，并估计结果的不确定性和鲁棒性进行蒙特卡洛型分析。结果表明，沿这些剖面的最大地壳厚度沿着从16.5 km（南科科斯）到19.9 km（北方科科斯和马尔佩洛）不等。无论地壳总厚度如何变化，第2大洋层的厚度都是相当均匀的;地壳增厚主要由第3大洋层提供。这些观测结果与重力数据一致。第三层速度沿各剖面沿着的变化规律相似，地壳越厚，速度越低。这就导致了地壳厚度与整体低地壳速度之间存在着一种总体上的正相关关系。由于这一关系与异常热地幔被动上涌导致的地壳增厚相反，因此有必要考虑地幔源区的主动上涌成分和/或某些成分的不均匀性。西北限制的Malpelo脊显示了显着的地壳变薄，并显示高的低地壳速度和一个不明确的壳幔边界，这表明差异运动沿着Coiba转换断层可能分开里贾纳和Malpelo脊。
[1] The Cocos and Malpelo Volcanic Ridges are blocks of thickened oceanic crust thought to be the result of the interaction between the Galapagos hot spot and the Cocos-Nazca Spreading Center during the last 20 m.y. In this work we investigate the seismic structure of these two aseismic ridges along three wide-angle transects acquired during the Panama basin and Galapagos plume—New Investigations of Intraplate magmatism (PAGANINI)-1999 experiment. A two-dimensional velocity field with the Moho geometry is obtained using joint refraction/reflection travel time tomography, and the uncertainty and robustness of the results are estimated by performing a Monte Carlo-type analysis. Our results show that the maximum crustal thickness along these profiles ranges from ∼16.5 km (southern Cocos) to ∼19 km (northern Cocos and Malpelo). Oceanic layer 2 thickness is quite uniform regardless of total crustal thickness variations; crustal thickening is mainly accommodated by layer 3. These observations are shown to be consistent with gravity data. The variation of layer 3 velocities is similar along all profiles, being lower where crust is thicker. This leads to an overall anticorrelation between crustal thickness and bulk lower crustal velocity. Since this anticorrelation is contrary to crustal thickening resulting from passive upwelling of abnormally hot mantle, it is necessary to consider active upwelling components and/or some compositional heterogeneities in the mantle source. The NW limit of the Malpelo Ridge shows a dramatic crustal thinning and displays high lower crustal velocities and a poorly defined crust-mantle boundary, suggesting that differential motion along the Coiba transform fault probably separated Regina and Malpelo Ridges.