藏北高原地壳及上地幔导电性结构: 超宽频带大地电磁测深研究结果

To study the resistivity structure of crust and upper mantle beneath northern and central Tibet, furthermore, discuss thermal behavior of north and central Tibet lithosphere, super-wide band magnetotelluric sounding profiles named line 500 and line 600 which belongs to INDEPTH (III) were finished in 1998 and 1999. The line 500 is from Dêqên to Longwei Co, and the line 600 is from Nagqu to Golmud. The results show that the boundary between northern Tibet and central Tibet is Kunlun fault, and the conductive structures of crust and mantle beneath northern and central Tibet are very different. North to the Kunlun fault the crust and upper mantle are resistive. But south to the Kunlun fault, the conductive structure of crust and upper mantle is in layers: in the upper crust, there are lots of discontinuous resistive bodies, and between them are local conductive bodies. From south to north the conductive structure of the upper crust is very complex and discontinuous, while the middle and lower crust is very conductive. There are lots of continuous, huge conductive bodies with different shapes, and their resistivities are all smaller than 4Ωm. Below the Bangong-Nujiang suture and Jinsha suture, the conductive bodies in the crust stretch into upper mantle, so they are conductive channels which connect crust and mantle. In northern and central Tibet there are also partial melted bodies ubiquitously related with heat transmission between crust and mantle below the Bangong-Nujiang suture and Jinsha suture, which formed in different stages. Moreover, the heat transmission channel between crust and mantle below the Bangong-Nujiang suture is older than that of the Jinsha suture. Therefore, heat activity in crust and mantle of Tibet began from south and west, spreading to north and east, which made the heat flow of crust and upper mantle of northern and central Tibet increase from west to east and from south to north.