北喜马拉雅及藏南伸展构造综述

A review on the extensional structures in the northern Himalaya and southern Tibet

印度与欧亚大陆碰撞发生于65Ma左右,造山作用则开始于中新世初期,该造山运动形成南喜马拉雅的逆冲推覆体系,导致喜马拉雅山脉的隆起。然而,与造山作用的同时,北喜马拉雅及藏南地区却经历了广泛的伸展作用,所形成的伸展构造包括:①北喜马拉雅地区,开始于24Ma左右的藏南拆离系(STDS);②北喜马拉雅及藏南地区,开始于14Ma左右的南北向裂谷;③北喜马拉雅穹隆带,形成时间大致与南北向裂谷相同;④广布于青藏高原、开始于中新世末期、随机分布的高角度正断层。上述不同阶段的伸展构造形成于不同机制,并在喜马拉雅造山带的发展过程中起着不同的地质作用。其中,北喜马拉雅穹隆是一种特殊的伸展构造,并可能形成于多种机制。

India-Asia collision occurred at -65 Ma; while mountain-building began in the early Miocene, which gave rise to a thrust system in the southem Himalaya, causing the Himalayan Mountains to be uplifted. However, in the process of the orogeny, the northern Himalaya and southem Tibet experienced extensive extension. The structures formed by the extension include： （1） the southem Tibetan detachment system in the northem Himalaya, which began to form at -24 Ma; （2） the north-south-trending rifts in the northem Himalaya and southern Tibet, which began to form at -14 Ma; （3） the northern Himalaya domes, which formed simultaneously with the N-S trending rifts; and （4） high-angle normal faults distributed randomly in the Qinghai-Tibet, which began to form at the end of the Miocene. The extensional structures at the different stages formed by different mechanisms and played different geological roles in the process of development of the Himalaya orogen. Among other thing, the northem Himalaya domes belong to a special type of extensional structure and probably formed by different mechanisms.