青藏高原南部洋板块地质重建及科学意义

Reestablishment and scientific significance of the Ocean plate geology in the Southern Tibet Plateau,China

在复杂碰撞造山带中发现、识别和重建能够揭示从洋中脊形成到海沟俯冲消亡洋陆转换过程的洋板块地层(OPS)单元及岩石组合序列,是大陆动力学研究的重大课题。本文在冈底斯地块南部与雅鲁藏布江结合带东段地区发现和识别出大量洋岛、海山、洋内弧、楔顶盆地、大洋盆地等洋板块地层。通过对该洋板块地层岩石组合序列、产出状态与变形变质特征与形成时代、构造环境等的初步研究,得出如下新的认识:(1)新发现的洋板块地层单元是雅鲁藏布江结合带东段在特提斯洋演化过程俯冲消减而形成增生杂岩带的重要组成部分;(2)在青藏高原南部古特提斯和新特提斯洋同时存在并连续演化;(3)南冈底斯带在中生代具有新特提斯增生楔和增生弧的地质背景,并且该增生楔是冈底斯南缘加厚新生下地壳的重要物质组成部分,对斑岩铜矿的形成起了促进作用。

Discovery and reestablishment of the ocean plate stratigraphy unit(OPS)and rock assemblage sequence in the complex collisional orogenic belt during the large scale ocean-continent conversion are important geodynamical and geological frontier issues.This paper reported new discoveries of the ocean plate stratigraphy including the ocean island,seamount,intra-oceanic arc,wedge-top basin,and oceanic basin,which are exposed at the eastern part of the Gangdese metallogenic belt and the Indus-Tsangpo Suture Zone in the Southern Tibet Plateau.Through detailed research on their rock assemblage sequence,occurrence,deforming,metamorphism,formation age and tectonic setting,we recognized that(1)the ocean plate stratigraphy unit is an important part of the accretionary complex,which is the result of the continental accretion in the southern Tibet Plateau during the Tethys evolution;(2)It is a continuous evolution from the paleo-Tethys ocean to neo-Tethys ocean in the Southern Tibet Plateau;and(3)The Mesozoic southern Gangdese belt is characterized by its geological setting of the neo-Tethys accretionary wedge,accretionary arc and the accretionary wedge.It is an important part of the thickening new lower crust at the southern margin of Gangdese,facilitating the formation of porphyry copper deposits in the areas.