南迦巴瓦构造结的楔入及其地质效应

The wedging of the Namjagbarwa syntaxis in southeastern Xizang and its geological effects

关键词:  南迦巴瓦构造结  楔入  滇藏涡旋构造  雅鲁藏布大峡谷

Key words:  Namjagbarwa syntaxis  wedging  Yunnan-Xizang whirl structure  Yarlung Zangbo Grand Canyon

摘要:

南迦巴瓦构造结由其核部的喜马拉雅构造单元和周边的冈底斯构造单元、雅鲁藏布构造单元组成。喜马拉雅构造单元为构造楔入体,两侧发育有右旋和左旋走滑断层系,构成南迦巴瓦楔入构造。由于南迦巴瓦构造结的楔入作用,使雅鲁藏布缝合线横推错位,形成滇藏涡旋构造,并为雅鲁藏布大峡谷的形成奠定了基础。南迦巴瓦楔入构造的形成与印度板块连续的向北汇聚推挤作用发生反时针旋转有关,并可分为点碰撞(45 Ma前)、碰撞楔入(45～7 Ma)和旋转抬升(7 Ma以来)三个阶段。

Abstract:

The Namjagbarwa syntaxis consists of three tectonic units: the central Himalayan tectonic unit, and marginal Gangdise and Yarlung Zangbo tectonic units. The Namjagbarwa wedge structures are represented by the Himalayan tectonic unit as a structural wedge, and its surrounding right- and left-dextral strike-slip faults systems. The wedging of the Namjagbarwa syntaxis, in turn, has permitted the transcurrent dislocation of the Yarlung Zangbo suture zone and the formation of the Yunnan-Xizang whirl structures, from which the Yarlung Zangbo Grand Canyon resulted as the most magnificent canyon in the world. The genesis of the Namjagbarwa wedge structures is interpreted to be related to the continuous northward compression and counterclockwise rotation generated during the northward shift of the Indian plate. The wedging processes include three stages of point collision (>45 Ma), collisional wedging (45-7 Ma) and rotational uplift (<7 Ma).