Deep 3D electrical structure in Eastern Tibet-Western Sichuan

We have obtained the deep structures and electric features through magnetotelluric prospecting in eastern Tibet and western Sichuan of the Tibetan plateau, and results show as follows:

- There are four faults running through the Moho surface on the survey line, namely the Jinsha rvier-Red river fault zone, the Anning river fault zone, the Xiaojiang fault zone, and the Jinyang-Ebian fault zone.

- There are seven main high conductors in the shell: (1) The high conductor of Gudong-Yushui may be a reflection of the magma sac in this area; (2) The high conductor in the west of Jinshajiang may be a low-resistance Silurian or Ordovician strata; (3) Heqing high conductor may be caused by magma melting; Both (4) Yongsheng-salt high conductor and (5) Dechang-Puge County high conductor may be caused by magma melting; (6) Puge-Jinyang high conductor may be caused by fracture water content of fracture zone; (7) The high conductor of southern Nannan may be caused by low-resistance Silurian, Ordovician strata or fault zone.

- The high-resistance body of the middle and lower crust of the Shuhezhen-Kangdian axis runs straightly through the mantle, which is with high gravity and relatively high magnetic anomalies. We speculate that this phenomenon is caused by upwelling and condensation of the mantle magma.It shows that there happened the lithosphere rupturing. A large amount of molten mantle rocks rushed up to a higher position along the faults, and formed a thick base-ultrabase accumulation inside the lithosphere, which is also a residual after partial melting of the mantle plum (Xu, 2004).

Research shows that there commonly appear two low-velocity and high-conductivity (LVHC) layers in the crust of Qinghai-Tibet Plateau. The upper LVHC layer in the Gangdese and the Himalayan orogenic belts. It trends to become shallower from the north to south. From the above results, we conclude that this LAHC layer may be a giant detachment layer caused by the Indian plate subducting northward in the upper part of the crust (or between the upper and middle crust). This detachment layer causes rock melting or fluid filling due to frictional heat forms the LVHC layer.

Thanks to the National Science and Technology Major Project of China ("2016YFC060110602" and "2016YFC0600306-5") and Jiangsu 814 geophysical exploration team for their strong support for this research.