A plume-modified lithospheric barrier to the southeastward flow of partially molten Tibetan crust inferred from magnetotelluric data
A plume-modified lithospheric barrier to the southeastward flow of partially molten Tibetan crust inferred from magnetotelluric data
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DOI：
10.1016/j.epsl.2020.116493
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发表时间：
2020-10
影响因子：
5.3
通讯作者：
Xin Li;Xiaobing Ma;Yun Chen;Shuai Xue;I. Varentsov;Denghai Bai
中科院分区：
文献类型：
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作者：
Xin Li;Xiaobing Ma;Yun Chen;Shuai Xue;I. Varentsov;Denghai Bai
利用宽频带和长周期大地电磁（MT）资料，获得了青藏高原东南缘岩石圈电导率结构的连续图像。青藏高原东南缘的长波地壳增厚和地表隆起是由于来自西藏的弱地壳物质流入邻近的扬子地块所致。由此产生的电阻率模型揭示了西藏东南部和楚雄盆地下地壳中的两个主要导电特征，这两个特征都与流体的存在相一致，并可能因沿沿着大断层的剪切变形而增强。西藏东南部的水平延伸导体可以解释为一个部分熔融层，代表地形驱动的地壳流动从西藏中部，而在楚雄盆地下观察到的异常高的电导率需要添加大量的盐水流体。这两个导体被一个岩石圈规模的高电阻率体所分隔，该体位于峨眉山大火成岩省（ELIP）的地质推断的核之下。结合其他地球物理和地质证据，我们将这种异常解释为二叠纪峨眉山火山活动期间最初形成的地幔柱改性岩石圈的残留物，并推测它对晚新生代以来从西藏向东南方向的地壳流动起到了阻碍作用。这些结果表明，地形驱动的地壳流动可能有助于西藏东南部的地壳加厚和隆升，但对邻近的前陆没有贡献。相反，与二叠纪地幔柱活动相关的岩浆底侵作用可以解释邻近扬子地块的地形升高和地壳增厚，而不需要地壳流动。
Broadband and long-period magnetotelluric (MT) data were used to obtain a continuous image of the lithospheric electrical conductivity structure across the southeastern Tibetan Plateau margin, where long-wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from Tibet into the adjacent Yangtze Block. The resulting resistivity model reveals two major conductive features in the middle–lower crust beneath southeastern Tibet and the Chuxiong basin, both of which are consistent with the presence of fluids and likely enhanced by shear deformation along large faults. The horizontally extensive conductor beneath southeastern Tibet could be interpreted as a partially molten layer that represents topography-driven crustal flow from central Tibet, whereas the anomalously high conductivities observed beneath the Chuxiong basin require the addition of substantial amounts of saline aqueous fluids. These two conductors are separated by a lithospheric-scale, high-resistivity body that situated beneath the geologically inferred core of the Emeishan large igneous province (ELIP). Together with other geophysical and geological evidence, we interpret this anomaly as remnants of a plume-modified lithosphere that originally formed during the Permian Emeishan volcanism, and speculate it acts as an obstruction to the southeastward crustal flow from Tibet since Late Cenozoic. These results indicate that topography-driven crustal flow may contribute to crustal thickening and uplift in southeastern Tibet, but not in the adjacent foreland. Instead, magmatic underplating associated with the Permian plume activity could account for both the elevated topography and thickened crust of the adjacent Yangtze Block without the need for crustal flow.