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Low electrical resistivity associated with plunging of the Nazca flat slab beneath Argentina

机译：低电阻率，与阿根廷下方的纳斯卡平板骤降有关

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Beneath much of the Andes, oceanic lithosphere descends eastward into the mantle at an angle of about 30degrees (ref. 1). A partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material(2). This wedge is the ultimate source for magma erupted at the active volcanoes that characterize the Andean margin. But between 28degrees and 33degrees S the subducted Nazca plate appears to be anomalously buoyant(3,4), as it levels out at about 100 km depth and extends nearly horizontally under the continent(1,5,6). Above this 'flat slab', volcanic activity in the main Andean Cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge(5,6). But it is unknown where slab volatiles go once this happens, and why the flat slab finally rolls over to descend steeply into the mantle 600 km further eastward. Here we present results from a magnetotelluric profile in central Argentina, from which we infer enhanced electrical conductivity along the eastern side of the plunging slab, indicative of the presence of partial melt. This conductivity structure may imply that partial melting occurs to at least 250 km and perhaps to more than 400 km depth, or that melt is supplied from the 410 km discontinuity, consistent with the transition-zone 'water-filter' model of Bercovici and Karato(7).
机译：在安第斯山脉的大部分地区，大洋岩石圈以约30度的角度向东向下进入地幔（参考资料1）。人们认为，由于该平板释放出的挥发物降低了地幔材料的熔融温度，在该下降平板和上覆大陆岩石圈之间的楔形部分形成了熔融区域（2）。该楔形岩是安第斯山脉边缘特征活跃火山喷出的岩浆的最终来源。但是俯冲的纳斯卡板块在28度到33度之间似乎是异常浮力的（3,4），因为它平缓了约100 km的深度，并在该大陆下几乎水平延伸（1,5,6）。在这块``平板''上，安第斯山脉主山脉的火山活动大约在900万年前终止，因为该平板被挤压出了地幔楔（5,6）。但是，这种情况一旦发生，板状挥发物就会流向何方，以及为何平坦的板状结构最终会翻滚而向下陡峭地向东延伸600公里，这是一个未知数。在这里，我们介绍了阿根廷中部大地电磁剖面的结果，从中我们推断出沿急流板东侧增强的电导率，表明存在部分熔体。这种电导率结构可能意味着部分融化发生在至少250 km处，也许深度超过400 km，或者融化是从410 km不连续处供应的，这与Bercovici和Karato的过渡带“滤水器”模型一致（7）。

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