Upper mantle electrical resistivity structure beneath the central Mariana subduction system
Upper mantle electrical resistivity structure beneath the central Mariana subduction system
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DOI：
10.1029/2010gc003101
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发表时间：
2010-09
期刊：
影响因子：
3.7
通讯作者：
T. Matsuno;N. Seama;R. Evans;A. Chave;K. Baba;A. White;T. Goto;G. Heinson;G. Boren;Asami Yon
中科院分区：
文献类型：
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作者：
T. Matsuno;N. Seama;R. Evans;A. Chave;K. Baba;A. White;T. Goto;G. Heinson;G. Boren;Asami Yon
本文报告了对马里亚纳中部俯冲系统进行的大地电磁 (MT) 调查，提供了上地幔的全面电阻率图像，以解决地幔楔和慢弧后扩张脊下方的地幔动力学问题。在计算 MT 响应函数及其对地形变形的校正后，使用具有平滑度约束和俯冲板片施加的附加限制的反演算法生成二维电阻率结构。由此产生的各向同性电阻率结构包含几个关键特征。太平洋盆地下方有一个厚度达 150 公里的最上层电阻层，马里亚纳海槽下方有 80-100 公里，帕雷塞维拉盆地下方有 60 公里，电阻层下方有一个导电地幔。推断在地幔楔的火山弧下方存在一个深达 60 公里的电阻区和一个更深处的导电区。没有证据表明弧后扩张中心下方存在导电特征。通过合成数据的反演对这些特征进行了敏感性测试。最上面的电阻层是极板增生过程中冷却、干燥的残留物。太平洋海盆下方的厚度主要受温度控制，而马里亚纳海槽下方和帕雷塞维拉盆地下方大致恒定的厚度（无论海底年龄如何）则受成分控制。最上面的电阻层下方的导电地幔需要橄榄石的水合和/或地幔的熔化。火山弧下方低至 60 公里的电阻区域表明，诸如熔体或自由水之类的流体没有很好地连接，或者是高度三维且尺寸有限的。相比之下，60公里深度以下火山弧下方的导电区域反映了俯冲板片释放水驱动的熔化和水化作用。弧后扩张中心下方的电阻区域可以用具有典型温度的干燥地幔来解释，这表明存在的任何熔体要么连接不良，要么沿山脊走向不连续分布。马里亚纳中部上地幔电各向异性的证据很薄弱。
This paper reports on a magnetotelluric (MT) survey across the central Mariana subduction system, providing a comprehensive electrical resistivity image of the upper mantle to address issues of mantle dynamics in the mantle wedge and beneath the slow back‐arc spreading ridge. After calculation of MT response functions and their correction for topographic distortion, two‐dimensional electrical resistivity structures were generated using an inversion algorithm with a smoothness constraint and with additional restrictions imposed by the subducting slab. The resultant isotropic electrical resistivity structure contains several key features. There is an uppermost resistive layer with a thickness of up to 150 km beneath the Pacific Ocean Basin, 80–100 km beneath the Mariana Trough, and 60 km beneath the Parece Vela Basin along with a conductive mantle beneath the resistive layer. A resistive region down to 60 km depth and a conductive region at greater depth are inferred beneath the volcanic arc in the mantle wedge. There is no evidence for a conductive feature beneath the back‐arc spreading center. Sensitivity tests were applied to these features through inversion of synthetic data. The uppermost resistive layer is the cool, dry residual from the plate accretion process. Its thickness beneath the Pacific Ocean Basin is controlled mainly by temperature, whereas the roughly constant thickness beneath the Mariana Trough and beneath the Parece Vela Basin regardless of seafloor age is controlled by composition. The conductive mantle beneath the uppermost resistive layer requires hydration of olivine and/or melting of the mantle. The resistive region beneath the volcanic arc down to 60 km suggests that fluids such as melt or free water are not well connected or are highly three‐dimensional and of limited size. In contrast, the conductive region beneath the volcanic arc below 60 km depth reflects melting and hydration driven by water release from the subducting slab. The resistive region beneath the back‐arc spreading center can be explained by dry mantle with typical temperatures, suggesting that any melt present is either poorly connected or distributed discontinuously along the strike of the ridge. Evidence for electrical anisotropy in the central Mariana upper mantle is weak.