青藏高原西南部南北向构造研究的新见解
The NS-trending structures in the southwestern part of the Qinghai-Xizang Plateau: New insights
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摘要: 广泛分布在青藏高原西南部的南北向构造,是高原新生代陆内汇聚变形的重要组成部分。经过中外学者40余年研究,至今已取得许多重要进展并形成了一些共识,也存在若干分歧。作者对南北向构造研究及某些共识的不同意见是:①南北向构造不仅有伸展构造形迹,还有褶皱、逆断、叠加等挤压构造形迹;②不能用裂谷系代表所有的伸展构造,也不能用裂谷系、地堑系等伸展构造名称代表高原西南部的全部南北向构造形迹。建议采用"南北向构造"这一包容性强的中性名称;③南北向构造最早产生于始新世-渐新世;④首先产生南北向伸展构造的是藏北羌塘-青南地区而非喜马拉雅地区;⑤大致在渐新世末-中新世初,青藏高原曾出现过一次短暂的东西挤压应力场,生成了各式挤压构造变形形迹。本文的新见解既丰富了南北向构造的成份与内涵,又可以此将南北向构造划分为早期(E2-3)伸展、中期(E3末-N1初)挤压、晚期(中新世及以后)再伸展3个发生、发展期。Abstract: Nunerous studies conducted in the southwestern part of the Qinghai-Xizang Plateau in the last decades have revealed that there has been considerable progress but still debate concerning the NS-trending structures in this vast area. These NS-trending structures represent an important part of the Cenozoic intracontinental convergent deformation on the Plateau. Some aspects of views from the author in the present paper are suggested as follows. (1) The NS-trending structures consist of not only the extensional structures but also the compressional structures such as folds, overthrust faults and superimposed structures. (2) The terminology rift systems can't be applied to represent all of the extensional structures,and the rift systems and graben systems also can't represent all of the NS-trending structural features. Instead, the NS-trending structures are herein suggested. (3) The NS-trending structures in the study area were initiated during the Eocene to the Oligocene. (4) The NS-trending extensional structures were initiated in the northern Xizang to southern Qinghai zone rather than in the Himalayas. (5) A phase of temporary EW-trending compressional stress field once occurred on the Plateau during the latest Oligocene to the earliest Miocene, and resulted in the formation of various compressional structures. The NS-trending structures outlined above show a long and complex history, with early initiation and development spanning three phases of extension during the middle and late Eogene, compression during the latest Eogene to the earliest Neogene, and reextension during the Miocene or later.