罗迪尼亚大陆西北缘俯冲作用:来自藏北安多拉伸纪花岗片麻岩的证据  

Oceanic subduction along the northwestern margin of the Rodinia:Evidence from the Tonian granite gneisses in the Amdo area,northern Tibet

作　　者：杨宁 胡培远[1] 翟庆国[1] 唐跃[1] 刘一鸣 李金勇 YANG Ning;HU Peiyuan;ZHAI Qingguo;TANG Yue;LIU Yiming;LI Jinyong(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2023年第6期1797-1814,共18页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42072268,41872240);第二次青藏高原综合科学考察项目(编号2019QZKK0703);国家重点研发计划(编号2021YFC2901901);中国地质科学院地质研究所基本科研业务经费(编号J2202);中国地质调查项目(编号20221630)联合资助的成果。

摘　　要：罗迪尼亚超大陆的古地理重建和各陆块拼接方案一直是中外地球科学家关注和竞相研究的热点和前沿。目前,青藏高原各陆块的起源及其在罗迪尼亚超大陆中的古地理位置尚不清楚,岩浆事件的对比研究是解决这一问题的有效方法之一。本文报道了青藏高原中部安多微陆块的拉伸纪花岗片麻岩的LA-ICP-MS锆石U-Pb定年、岩石地球化学和锆石Hf和全岩Sr-Nd同位素分析结果。这些花岗片麻岩的原岩形成于802~801 Ma,具有不均一的锆石Hf和相对均一的全岩Nd同位素成分(ε_(Hf)(t)=9.4~+1.9;ε_(Nd)(t)=4.8~3.4)以及古老的地壳模式年龄(2289~1575 Ma),可能形成于幔源岩浆对元古宙地壳的改造,随后经历了广泛的结晶分异过程。花岗片麻岩样品具有较低的P_(2)O_(5)含量,P_(2)O_(5)与SiO_(2)含量呈负相关性,且含少量角闪石矿物,符合I型花岗岩的特征,其中部分样品具有较高的高场强元素含量(Zr+Ce+Nb+Y>350×10^(-6))和锆石饱和温度(> 800℃),因而兼具A型花岗岩的特征。综合前人研究成果与区域地质背景,中国安多地区拉伸纪花岗片麻岩可能形成于弧后盆地环境,与马达加斯加、塞舌尔和印度西部的同时代岩浆记录可以对比,从而为重建罗迪尼亚超大陆提供了新的依据。The paleogeographic reconstruction of Rodinia supercontinent and the scheme of blocks have always been the focus and frontier of earth scientists at home and abroad.At present,the origin and paleogeographic location in the Rodinia supercontinent of the blocks in the Qinghai-Tibet Plateau are not clear.The comparative study of magmatic events is one of the effective methods to solve this problem.In this paper,LA-ICP-MS zircon U-Pb dating,petrogeochemistry,and zircon Hf and whole-rock Sr-Nd isotopic analyses of the granitic gneisses from the Amdo microcontinent in the central Tibetan Plateau are reported.The protoliths of these granitic gneisses were formed at 802~801 Ma,have heterogeneous zircon Hf and homogeneous whole Nd isotopic compositions(ε_(Hf)(t)=9.4~+1.9;ε_(Nd)(t)=4.8~3.4) and ancient crustal model ages(2289~1575 Ma),and were probably generated by melting of mantle-modified Proterozoic crust and subsequent extensive crystallization differentiation.All samples have low P_2O_(5) contents,that is negatively correlated with SiO_(2) contents,and the samples contain a small amount of hornblende minerals,which is similar to those of I-type granite.Some rocks have high contents of high field strength elements(Zr+Ce+Nb+Y350×10~(-6)) and zircon saturation temperature(800℃) of A-type granite affinitiy.Finally,we propose that the granitic gneisses were probably formed in a back-arc basin environment,and could be compared with coeval magmatic rocks in Madagascar,Seychelles,and western India.This work provides new information for reconstruction of the Rodinia supercontinent.

关 键 词：青藏高原 安多微陆块 全岩地球化学 锆石U-PB定年 

分 类 号：P588.345[天文地球—岩石学] P542[天文地球—地质学]