کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6434129 | 1636781 | 2013 | 11 صفحه PDF | دانلود رایگان |
- 700Â km deep cross-section along the Lhasa-Golmud transect across Tibet is presented.
- New INDEPTH project results change the image of the northern part of the plateau.
- Songpan-Ganzi lower crust underthrusts or flows northward beneath the Qaidam Moho.
- Asian lithospheric mantle is overlain by a separate Tibetan plate.
- Tibetan plate consists of both an upper lithospheric and a lower asthenospheric part.
A 700Â km deep seismic velocity cross-section beneath the Lhasa to Golmud transect across the Tibetan plateau is presented. In contrast to the first version of this cross-section, which comprised an 800Â km wide swath centred on the Lhasa to Golmud transect, due to the recent proliferation of publications concerning the mantle structure beneath Tibet, this study is based only on seismic profiles which either run along or cross the transect and arrays or studies which at least partly cover the transect. The results from the recent INDEPTH IV project indicate that the crustal thickness change from 70Â km beneath the Songpan-Ganzi terrane and Kunlun mountains to 54Â km beneath the Qaidam basin is located about 100Â km north of the Kunlun Fault and almost 45Â km north of the North Kunlun Thrust. The Qaidam basin Moho is underlain by crustal velocity material for almost 45Â km and the apparently overlapping crustal material may represent Songpan-Ganzi lower crust underthrusting or flowing northward beneath the Qaidam basin Moho. Thus the high Tibetan plateau may be thickening northward into south Qaidam as its weak, thickened lower crust is injected beneath the stronger Qaidam crust. Beneath the crust, high-velocity, dense, cold Indian lithospheric mantle extends northwards until about the Banggong-Nujiang suture. Northwards, Asian lithospheric mantle is overlain by a low-velocity, less dense, warm Tibetan plate consisting of an upper lithospheric and a lower asthenospheric part. The apparent northwards deepening of the 410 and 660Â km discontinuities by about 20Â km implies that the upper mantle beneath north Tibet is slower, less dense and warmer than under south Tibet, in agreement with the observed uppermost mantle velocities. This, in turn, could provide some of the isostatic support for the high elevations in the north where the crust is somewhat thinner than in the southern plateau.
Journal: Tectonophysics - Volume 606, 23 October 2013, Pages 187-197