青藏高原北部沱沱河—格尔木地区的地壳结构和深部作用过程

THE CRUSTAL STRUCTURE AND DEEP INTERNAL PROCESSES IN THE TUOTUOHE-GOLMUD AREA OF THE NORTH QINGHAI-XIZANG PLATEAU

通过对沱沱河—格尔木地区地震测深资料的重新解释,给出了该区地壳的二维速度分布剖面及Q值分布。上地壳横向速度结构具有明显的分区性。该分区范围大体与“亚东—格尔木项目”中所划分出的地体相一致。地震资料为本区划分地体提供了佐证。 本文讨论了地体的拼合、碰撞的深部作用过程。认为上地壳的逆冲、叠覆,中、下地壳的挤压增厚,以及岩浆的贯入,壳幔物质的混合导致了青藏高原的隆升。

Recalculation and interpretation of the available explosive seismic sounding data in the Tuotuohe-Golmud area has resulted in a two-dimentional velocity structural model and distribution of Q values. The result shows that the crust in the region is characterized by vertical structural stratification and lateral velocity heterogeneity. The upper crust has clear zonal velocity structure. In the lower part of the upper crust is widely distributed low velocity zone. The upper crust is shown as velocity gradient zone. The velocity ranges from 4.0 to 6.2km/s and the thickness is between 14 and 18km. The low velocity zone is 3-5km thick, and zonal velocity is 5.7-5.8km/s. It may be interpreted as water-bearing decollement strata. Its Q value is 52-150. The middle crust is generally uniform with a thinckness of 12-18 km and stratum velocity of 6.3-6.4km/s. Q value is 101-158. The lower crust, 25-34km thick, is divided into two strata. The upper stratum is generally unifom with a thinckness of 19-28 km and stratum velocity of 6.5 km/s. The lower stratum is shown as velocity gradient one with 10-14 km in thinckness and the velocity ranges from 6.7 to 8.1 km/s. The bottom of the lower stratum is called a new MOHO. The new MOHO may be interpreted as a boundary formed since the Palaeozoic. The crstal thinckess is 58 km in the Golmud area and 66km in the Tuotuohe area. The average crust velocity is 6.3-6.13 km/s. Its Q value is 166-368. And this area is conside- red to be isostatic.The velocity structure of the upper crust has clear lateral zonal feature, which are generally coincident with the divided terrains. Therfore, the structural characteristics of the upper crust may provide evidence for the division of the terrain.This paper discusses making-up, collision and deep-internal processes of the area.The uplift of the Qinhai-Xizang (Tibet) Plateau is due to the thrusting and overlapping of the upper crus; compressing and thickening of the middle and lower crust; injection of magma and mixture of materials from the crust and mantle. It is thought that such a high and steep plateau was formed through the making-up of the Indian shield, the Yangtze platform, and the Qaidam massive.