| 青藏高原深部地质特征及其形成机制探讨 |
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| CHARACTERISTICS OF DEEP-SEATED GEOLOGY IN THE QINGHAI-XIZANG (TIBET) PLATEAU AND MECHANISM OF ITS FORMATION |
| The explosive seismic sounding made by the Chinese-French Joint Geological Party in Tibet during 1981-1982 has confirmed that there is a 75km thick crust between the Yarlung Zangbo River and the Himalayas which becomes thinner both southwards and northwards, and the crust of the High Himalayas is only 55 km thick without a mountain root. The crust in Tibet is divided approximately into two layers, the upper and the lower. Both of them have a velocity close to the normal one. The faults of the two layers often dip in opposite directions and between the two usually occur a low-velocity layer and a stable interface. These features mean that instead of double crust and great insertion, both the upper and lower crusts are double in thickness. The crustal structures of the Himalayas and the Gongdise tectonic belts are similar in general but sometimes different from each other.Across the strike of the tectonic belts, there is a uniquely deep Moho trough underneath both in the south of the Yarlung Zangbo River fault and the Nujiang River fault. The deep Moho trough of the former gets thinner towards both the sides of its crust and is controlled by extrodipping thrusts. On the northern side of this trough, the Moho is overlapped as imbrication. The thrusts that cut the Moho on the both sides appear as ramp faults. All of these prove that the India craton has never subducted under the Tibet crust, but on the contrary has obducted onto it.The features of the crustal and deep-seated sturctures in Tibet indicate that great horizontal stress which moves southwards from the northern side of the Qinghai-Tibet Plateau made the crust of this region be in a high compressed state caused by its northern and southern landmasses over a long period. The crust became eventually folded and thrusted at the beginning of the Himalayan orogeny, and the fault walls were overlapped on or ramped each other. Accordingly, the Tibet crust has shortened in a meridional direction and thickened or elevated vertically. The rapid elevation of the Plateau's crust took place probably at the end of the Himalayan orogeny, because the river system of low watershed on the south side has flowed across the Himalayas ever since that period. The no-mountain-root High Himalayas suggests that the elevation of the Plateau has not resulted from gravity balance effect,and subsidence of the Moho into the depth of 75 km could not complete only by horizontal tectonic stress. Therefore it is inferred here that both horizontal tectonic stress and gravity balance effect led to the formation of the Qinghai -Tibet Plateau. |
| CUI Zuo-zhou.1987.CHARACTERISTICS OF DEEP-SEATED GEOLOGY IN THE QINGHAI-XIZANG (TIBET) PLATEAU AND MECHANISM OF ITS FORMATION[J].Acta Geoscientica Sinica,9(3):1-15. |
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