Clockwise rotation of the entire Oman ophiolite occurred in a suprasubduction zone setting
Clockwise rotation of the entire Oman ophiolite occurred in a suprasubduction zone setting
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整个阿曼蛇绿岩的顺时针旋转发生在超俯冲带环境中
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
C. MacLeod
中科院分区：
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作者：
A. Morris;M. Meyer;M. Anderson;C. MacLeod
阿曼蛇绿岩为研究大洋岩石圈过程提供了天然实验室。以前的古地磁和构造研究已经被用来支持一个模型，该模型涉及在大洋中部微板块形成过程中蛇绿岩的旋转。然而，最近的地球化学证据表明，蛇绿岩反而是在新生的弧前环境中形成的，这为替代旋转机制打开了可能性。这个难题的中心是来自北部和南部蛇绿岩地块的ESE到SE磁化和NNW磁化之间的对比，以前被归因于扩张过程中的不同构造旋转或南部地块与侵位有关的完全再磁化。在这里，我们报道了来自南部地块下部地壳岩石的新的古地磁数据，这些数据解决了这个问题。Wadi Abyad连续剖面的采样显示，在下地壳顶部的岩脉根带中，ENE磁化作用在下部面片状和层状辉长岩中系统地向下向NNW方向变化。这只与从底部向上的再磁化一致，完全取代了层状和片状辉长岩中的早期剩磁，但在更高的水平上保留了原始的ENE磁化。与Wadi Khafifah的新数据相比，Khafifah提供了一个正褶皱检验，表明该事件发生在晚寒武世构造破坏岩石学莫霍面区域方向之前。这些资料表明，在部分再磁化之前，整个蛇绿岩经历了较大的大洋内顺时针旋转，形成了一种新的构造模式，蛇绿岩的形成、旋转和侵位都与阿拉伯晚白垩世的运动和阿曼俯冲带的卷退有关。
The Oman ophiolite provides a natural laboratory for understanding oceanic lithospheric processes. Previous paleomagnetic and structural investigations have been used to support a model involving rotation of the ophiolite during formation at a mid-oceanic microplate. However, recent geochemical evidence indicates the ophiolite instead formed in a nascent forearc environment, opening the potential for alternative rotation mechanisms. Central to the conundrum is the contrast between ESE to SE magnetizations and NNW magnetizations from the northern and southern ophiolitic massifs respectively, attributed previously to either differential tectonic rotations during spreading or complete emplacement-related remagnetization of the southern massifs. Here we report new paleomagnetic data from lower crustal rocks of the southern massifs that resolve this problem. Sampling of a continuous section in Wadi Abyad reveals ENE magnetizations in the dike rooting zone at the top of the lower crust that change systematically downwards to NNW directions in underlying foliated and layered gabbros. This is only consistent with remagnetization from the base upwards, replacing early remanences in layered and foliated gabbros completely but preserving original ENE magnetizations at higher levels. Comparison with new data from Wadi Khafifah provides a positive fold test that shows this event occurred before late Campanian structural disruption of the regional orientation of the petrologic Moho. These data show that the entire ophiolite experienced large intraoceanic clockwise rotation prior to partial remagnetization, leading to a new tectonic model in which formation, rotation and emplacement of the ophiolite are all linked to Late Cretaceous motion of Arabia and roll-back of the Oman subduction zone.