西部林子宗群火山岩源区组成对拉萨地块东部与西部壳幔归属的指示

It has been recognized that there are clearly geogical and geophysical differences between western and eastern Lhasa block, however, reasons of the differences are still unclear. Linzizong volcanic rocks (K-T) widely occur in western and eastern Lhasa block, but a few studies focused on those of the western. This project will mainly investigate the Linzizong volcanic rocks in western Lhasa block. Mineralogy (magmatic melt inclusion), petrology and geochemistry of these volcanic rocks will been studied in detail, their eruption time will be determined, meanwhile crust-mantle source compositions of the volcanic rocks and chemical variation are recognized. Then, comparing Linzizong volcanic rocks in western block with those from eastern block, this project trys to conclude the compositional differernce of crust and mantle below western and eastern Lhasa block, and illustrate what result in these differences, as well as insight into crust and mantle adscription beneath eastern and western part of Lhasa block. Our study will lead to better understand tectonic evolution of western and eastern part during collision between the India and Asian continents, and provide more geological and geochemical evidences.

青藏高原拉萨地块的东部与西部存在明显的地质地球物理差异，但是导致这种差异的原因仍不清楚。晚白垩世-始新世林子宗群火山岩广泛分布在拉萨地块的东部和西部，目前对西部林子宗群火山岩还缺乏系统的地质学、地球化学研究。本研究拟以拉萨地块西部代表性的林子宗火山岩为主要研究对象，通过对其内部各个组成单元火山岩的矿物学（熔融包裹体）、岩石学和地球化学系统解剖，限定出西部林子宗火山岩的喷发年代和上下时限，查明这些火山岩的壳、幔源区组成和演变，并与拉萨地块东部典型剖面的林子宗群火山岩进行系统的对比，揭示拉萨地块西部和东部之下地壳和地幔组成是否存在系统差异，从而进一步探讨导致青藏高原拉萨地块东西存在差异的原因，鉴别拉萨地块的东部和西部岩石圈的可能归属，为讨论青藏高原陆陆碰撞过程中东部与西部的构造演化提供有效的地质和地球化学约束。

结题摘要（中文）通过对青藏高原西部林子宗群火山岩、同时代的中基性侵入岩脉带以及班公湖-怒江带榴辉岩等的系统研究，本项目查明了林子宗群火山岩的形成时代(45-64 百万年)，最早喷发的林子宗火山形成在约64百万年，揭示出西部与东部林子宗群火山岩的主要差异受拉萨地块西部和东部地壳和地幔成分差异的制约；对厘定出的同期东西向伸展中基性侵入岩脉研究，指示出在林子宗群火山岩的形成过程中发生了俯冲或碰撞挤压之后区域伸展的构造转变，表明可能存在的俯冲板片断离过程；在林子宗群中识别出一些更老的侏罗纪和白垩纪的岩浆产物，总结出它们是古老的侏罗纪和白垩纪岩浆弧的产物；另外，我们还首次在班公湖-怒江蛇绿-混杂岩带中，发现了真正的高压变质形成的洋壳型榴辉岩，揭示出班公湖-怒江洋曾经经历过洋盆的俯冲消减、和之后的大陆碰撞过程。