| 西藏南部三叠纪沉积-构造演化 |
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| 引用本文：刘训,傅德荣,姚培毅.1990.西藏南部三叠纪沉积-构造演化[J].地球学报,11(2):9-20. |
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| 中文摘要:从三叠纪开始,西藏南部的沉积-构造特征开始发生分异,可区分出具不同沉积类型的4个带:1)喜马拉雅带——陆棚浅海;2)拉轨岗日带——上部陆坡深浅海—次深海;3)雅鲁藏布带——下部陆坡-陆隆次深海—深海;4)拉萨-邱桑带——早期陆内“裂陷槽”。三叠纪时,特提斯-喜马拉雅洋尚处于扩张初期,未形成宽阔的洋盆,也没有明显的俯冲,本区前三个带属于该洋盆南侧、印度板块北部的被动大陆边缘。株罗纪以后,洋盆两侧才形成了两种不同类型的大陆边缘。 |
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| THE TRIASSIC SEDIMENTARY-TECTONIC EVOLUTION IN SOUTHERN XIZANG |
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| Abstract:Triassic was the major time when the Tethys ocean in the world developed and the Yarlung Zanbo zone extended. The sedimentary-tectonic evolution in southern Xizang was a part of the tethys in the world and related with the spliting and extension of this suture zone. Based on the analysis of the sedimentation and tectonic evolution of Triassic rocks in this area, we reveal some characteristics about the early stage of evolution in this area.In this paper, we divided the Triassic rocks of southern Xizang into four facies belts, as follows:1)Himalaya belt, 2) Larguigangri belt, 3)Yarlung Zangbo belt and 4) Lhasa-Qiusang belt. In each belt, the sedimentation was characterized by himself.The Himalaya belt was the passive continental margin on the northern side of Indian plate. In Triassic, especially in early and middle Triassic, there were some terrestrial-carbonaceous formation, in which the various shallow sea environment were included, such as carbonate plateforms, organic banks, oolitic shoels, tidel flats et al. Laterally, their facies and thickness were more steady without sharply changing, showing a kind of stable plate-form-type sedimentation. At the upper part of Late Triassic, thick fluvio-delta facies clastic deposits accumulated in the belt, that implied a brief crust uplift and a minor regression, which would be produced by the Indo-sinian crust movement.In Larguigangri belt, the Triassic rocks made of deeper shallow sea to bathysal facies fine clastic deposits in upper part of continental slope, corresponding to some "miogeosynclinal deposits". There were a series of bathysal to abyssal argillaceous-siliceous deposits with a number of distinct olistostromes and violent volcanic activities in Yarlung Zangbo belt. It is considered that the Yarlung Zangbo belt presented a open ocean, but the abundance of terrestrial clastic and absence neither the material of oceanic crust nor the sediments that accumulated on the oceanic crust, suggested that Yarlung Zangbo belt had not been an open oceanic basin during Triassic. What is more, it is considered that the source of deposits was from the Gangdesi Mts. of north side, and presumed that the sediments above mentioned in Yarlund Zangbo belt were the products of the sedimentation on the northern slope of basin.Generally, the Triassic rocks of Lhasa-Qiusang belt belonged to the products of a early aulacogen, which was characterized by the narrow distribution, rapid accumulation, thick clastic and carbonate deposition with low maturity as well as violent volcanic activities of alkaline series. By late Triassic, because of the occurence of Gangdesi magmatic arc, the aulacogen closed and transformed a embryonic form of a baekarc basin.On the whole, the evolution of the Triassic sedimentary-tectonic evolution in southern Xizang marked the early development of Neo Tethys ocean, presented by the Yarlung Zangbo suture zone. The tectonic framework, that there was a passive continental margin from the northern slope of Himalaya to Larguigangri belt and a trench-arc-basin system from Yarlung Zangbo to Lhasa area, began to form during Triassic, especially in late Triassic, and by Jurassic to Cretaceous, the feature of this framework were more obvious. |
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