雅鲁藏布中新生代深水沉积盆地形成和演化(Ⅲ)——喜马拉雅被动大陆边缘构造沉降分析

FORMATION AND EVOLUTION OF THE MESOZOIC AND CENOZOIC DEEP-WATER SEDIMENTARY BASINS ALONG THE YARLUNG ZANGBO RIVER (Ⅲ): TECTONIC SUBSIDENCE OF THE HIMALAYAN PASSIVE CONTINENTAL MARGINS

关键词:  反剥法  盆地构造沉降  热耗散沉降  构造沉降曲线

Key words:  Backstripping  tectonic subsidence of sedimentary basins  thermal subsidence  tectonic subsidence curves

摘要:

喜马拉雅特提斯中、新生代属印度板块北部被动大陆边缘。对充填这个被动大陆边缘的沉积物用“反剥法”(backstrippiog)进行研究,恢复了从被动大陆边缘到前陆盆地的抓降史。对分离出的盆地构造沉降曲线与McKenzie模式图版进行对比相关性分析,判断认为被动大陆边缘成熟期主要为热耗散沉降,前陆盆地时逆冲推覆动力为主要影响因素。

Abstract:

The dynamic processes of the formation and evolution of the Himalayan passive continental margins are researched with the aid of the "backstripping" method. On the basis of tectonic subsidences in the areas from Nyalam to Yarlung Zangbo suture zone, the dynamic evolution of the sedimentary basins on the Himalayan passive continental margins are "summarized as follows. The continental rifts and continental margin rifts were controlled by the extensional faulting during the Triassic to Middle Jurassic. The rapid thermal subsidence occurred in the early formation stage of the passive continental margins in the Late Jurassic, while the slower linear thermal cooling subsidence was developed in the complete maturation stage of the passive continental margins in the Early Cretaceous. The subduction of the Indian plate towards the Gangdise block in the Late Cretaceous gave rise to an additional tectonic subsidence, as indicated by the tectonic subsidence curves for the Kangmar-Yarlung Zangbo zone. On the contrary, there was a slight tectonic uplift in the Nyalam-Gamba region-due to the compression of the crust in this region. The tectonic subsidences of the sedimentary basins still lasted in the Palaeocene probably because of the continent-continent collision. During this period, the amount of the subduction of the Indian plate was not very large, therefore the sedimentary wedges of the foreland sedimentary areas were less developed, and the sediment thickness was not very great. All these characteristics show that the mountains were not so high during the early stage of the plate collision. In the Eocene, the tectonic uplift occurred in the whole study area, with greater uplift rates on the northern Indian plate margin. Finally, the submarine topography was overturned and the sea water retrograded from the Himalayan region from north to south, suggesting the compression and uplift of the plate tectonics.