中国西部的大陆构造格架

CONTINENTAL TECTONIC FRAMEWORK OF WEST CHINA

在我国实施“西部大开发”战略的过程中 ,对中国西部大陆构造格架的正确认识至关重要 ,作者在近十余年研究的基础上提出三点新认识 :1.根据近年对阿尔金断裂带内同变形期新生矿物的激光微区 40 Ar/39Ar测年结果 ,阿尔金断裂走滑变形可能起始于 97～ 89Ma,它与喜马拉雅“西构造结”的形成 (10 2～ 85 Ma)近于同步 ,其累积错距达 35 0～ 40 0 km左右 ,晚白垩世—新生代同步错移了两侧原有的构造带和原型盆地。因此 ,在讨论中国西部大陆构造格架的形成时 ,首先考虑新生代由于喜马拉雅运动所引起的大尺度构造位移 ;2 .组成中国西部大陆的地块分属于北亚型、扬子型和冈瓦纳型。其中塔里木、柴达木、阿拉善地块 ,古生代期间是一个统一的扬子型非稳定克拉通——西域板块 ,震旦纪—早古生代它和扬子—华南、印支、澳大利亚板块同样隶属于东风瓦纳大陆 ,而后裂解、漂移 ,晚古生代—印支期构造就位于贺兰山以西 ,喜马拉雅期被肢解、错移成现今被分隔的盆地 (地块 ) ;3.北祁连山早古生代不是大洋盆地 ,而是西域克拉通陆内裂解出现洋壳的拗拉槽—小洋盆 ,它的西延部是塔里木盆地北部的满加尔—阿瓦提坳陷 ,新生代被阿尔金断裂左行错移达到现今的位置。北祁连山最终的造山作用 ,发生在上新世到早更新世末 。

In the process of carrying out 'West Development'policy,the tectonic outline of West China continent is very important for the exploration of oil and gas and other mineral resources.According to the recent researches,we have got three new understandings of West China tectonic:(1)The studies of laser probe 40 Ar/ 39 Ar dating in deformed rocks in Altyn fault suggest that the strike slip event occurred or began at 97~89 Ma. These ages are consistent with the formation ages (102~85Ma) of the so called'Western Tectonic Joint' in Himalayan.Sinistral strike slip shearing has caused displacement to 350~400km along the Altyn fault zone,and tectonic zones and original basins are displaced from Late Cretaceous to Cenozoic.Therefore,the large scale displacement must be taken into consideration when discussing the formation of the tectonic framework of Northwest China,including the reconstructions of the Precambrian blocks (including Rodinia super continent),tectonic zones and orignal basins from Mesozoic to Early Tertiary.(2)The Tarim,Qaidam and Alxa block formed a Yangtze type non staleb craton in Paleozoic,called Western Craton,which is characterized by multiphase breaking at different locations,and together with the Yangtze South China,Indosinian,Australian plates compose the Gondwana continent during Late Sinian Early Paleozoic.The super continent broken up and drifted later.The blocks are tectonically displaced and located during Late Paleozoic Indosinian stage.They are further broken up and displaced during Himalayan stage and form separated basins (blocks).(3)The North Qilian Mountains is an Aulacogen formed due to the intra continent breakup of the West China craton,instead of an oceanic basin,during Early Paleozoic.The west extension of the aulacogen goes to the Manjia'er Awati depression at north central Tarim.The present framework and distribution are due to the sinistral displacement by the Altyn fault in Cenozoic.The Paleo Qilian Mountain was formed during the closing of the aulacogen in Paleozoic.Planation was preceded during Paleozoic through Triassic and the mountain belt was transformed into cratonic basin.Due to extension during Jurassic to Early Tertiary,the North Qilian Mountains formed part of the original Hexi Corridor land basins.The formation of the present Qilian Mountains occurs from Pliocene to Early Pleistocene during the uprising of the Qinghai Tibet Plateau.