阿尔金南缘榴辉岩带中花岗片麻岩的时代及构造环境探讨

阿尔金南缘榴辉岩带中花岗片麻岩的时代及构造环境探讨

王超，刘良，车自成，陈丹玲，张安达，罗金海

大陆动力学国家重点实验室、西北大学地质系,西安 710069

收稿日期:2006-03-20 修回日期:2006-03-20 出版日期:2006-03-20 发布日期:2006-03-20

U－Pb Geochronology and Tectonic Setting of the Granitic Gneissin Jianggaleisayi Eclogite Belt，the Southern Edge of Altyn Tagh

WANG Chao, LIU Liang, CHE Zi-cheng, CHEN Dan-ling, ZHANG An-da, LUO Jin-hai

State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xian 710069, China

Received:2006-03-20 Revised:2006-03-20 Online:2006-03-20 Published:2006-03-20

摘要/Abstract

摘要： 阿尔金南缘江尕勒萨依一带榴辉岩的围岩花岗片麻岩具有高SiO2（〉70％）、高铝（Al2O3〉13％）和高碱（ALK=7．52-8．91）的特征，铝饱和度指数ASI=1．10～1．27，属于钙碱性过铝质花岗质岩石；岩石强烈富集大离子亲石元素Rb和Th，中等富集K和Ba，亏损高场强元素Nb，Zr，Hf，Y和Yb；具典型大陆碰撞型花岗岩相应的元素丰度特征；岩石的稀土元素含量较高，轻、重稀土分馏明显，总体呈右倾的“V”型稀土配分模式，显示壳源型花岗岩特征；在R1-R2构造环境判别图上落于同碰撞花岗岩区。锆石的阴极发光图像和微量元素分析结果显示了典型岩浆钻石的特征，利用LA-ICP-MS方法进行锆石微区U-Pb同位素定年，得到^206Pb/^238U加权平均年龄值为923±13Ma，表明江尕勒萨依花岗片麻岩的原岩形成时代为新元古代早期。阿尔金新元古代同碰撞花岗岩的确定，不仪明确了新元古代早期陆块汇聚在该区的存在，而且对区内新元古代早期造山作用的鉴别，重塑西部古大陆的演化历史、构造格架以及探讨它们之间的关系都有十分重要的意义，同时对于深入探讨区内高压-超高压岩石与围岩之间的相互关系提供了重要的约束资料。

Abstract: Geochemical studies on the Jianggaleisayi granitic gneiss suggest that the rocks are characterized by SiO2>70％，Al20 3>13％，Na2O +K2O =7．52％～8．91％，and with ASI=1．10～ 1．27，belonging to syn-eollisional S-type granite．The chondrite-normalized REE patterns are right-inclined，with a clear"V"trough，belonging to the granite of crustal source．The midocean ridge granite-normalized trace element spidergrams are characterized bv enriched LILE(such as Rb and Th)and depleted HFSE(such as Nb，Zr，Hf，Y，and Yb)．0n the R1～ R2 tectonic discrimination diagram they are plotted in the typical continent-continent syn-collisional granite field．The CL investigations reveal that zircons from the granitic gneiss are generally colourless，transparent and eu'hedral。and have distinct zoning of oscillatory bands，typical of magmatic origin．By means of LA-ICP-MS U-Pb isotopic dating．the zircons yielded a weighted average 206Pb／238U age of 923±13(2σ)Ma and indicative of Neoproterozoie time．Combined with the Neoproterozoic syn-collisional granite obtained from adjacent area，it is suggested that a collision and convergence between microcontinents in NW China took place during the Neoproterozoic time．This is very important not only for determining the existence of Neoproterozoic orogeny and for reconstructingthe tectonic evolution of the ancient continents in northwestern China，but also for providing constraints for discussing the relationship between the HI 一UHPM rocks and their country gneisses in the study area.

王超，刘良，车自成，陈丹玲，张安达，罗金海. 阿尔金南缘榴辉岩带中花岗片麻岩的时代及构造环境探讨[J]. J4.

WANG Chao, LIU Liang, CHE Zi-cheng, CHEN Dan-ling, ZHANG An-da, LUO Jin-hai. U－Pb Geochronology and Tectonic Setting of the Granitic Gneissin Jianggaleisayi Eclogite Belt，the Southern Edge of Altyn Tagh[J]. J4.