青藏高原拉萨地体北部的前寒武纪变质作用及构造意义

Precambrian Metamorphism of the Northern Lhasa Terrane,South Tibet and Its Tectonic Implications

青藏高原南部拉萨地体中分布的角闪岩相至麻粒岩相变质岩一直被认为是前寒武纪变质基底,但并没有获得可靠的年代学证据。本文运用原位锆石U-Pb定年方法,在拉萨地体北部那果地区的变质岩中获得了约720Ma的变质年龄,从而证明拉萨地体北部在新古元代经历了角闪岩相变质作用和近同期的岩浆作用。基于这一成果和在拉萨地体中、南部高级变质岩中陆续获得的中、新生代变质年龄,对拉萨地体变质作用的时、空变化及其成因进行了初步探讨。

The amphibolite-facies and granulite-facies metamorphic rocks in the Lhasa terrane,south Tibet,were considered traditionally as the Precambrian metamorphic basement,but the related geochronological evidence is lack.In this paper,we report a metamorphic age of ～720 Ma obtained from zircons of a marble collected from the Naguo area of northern Lhasa terrane.This data,together with the coeval magmatism in the same area,indicate that the northern Lhasa terrane has been subjected to the Neo-Paleozoic tectonic-thermal event.Based on this result and some Mesozoic and Cenozoic ages obtained recently from the high-grade metamorphic rocks in the central and southern segments of the Lhasa terrane,we propose a preliminary temporal and spatial evolution model for the multistage metamorphic processes of the Lhasa terrane.