新疆阿奇山岩体LA-ICP-MS锆石U-Pb年龄、Sr—Nd—Pb同位素特征及其成因探讨  

LA-ICP-MS zircon U-Pb Age,Sr—Nd—Pb isotopic compositions of Aqishan pluton in Xinjiang and their petrogensis significance

作　　者：田明明[1] 何建国[1] 张松[1] 高红雷 孔维豪[1] 李平[1] TIAN Mingming;HE Jianguo;ZHANG Song;GAO Honglei;KONG Weihao;LI Ping(Beijing Research Institute of Uranium Geology,Key laboratory of Uranium Resource Exploration and Evaluation Technology,CNNC,Beijing,100029)

机构地区：[1]核工业北京地质研究院中核铀资源勘查与评价技术重点实验室

出　　处：《地质论评》2020年第1期141-156,共16页Geological Review

基　　金：“高放废物处置库新疆预选区阿奇山地段候选场址筛选与评价研究”项目资助的成果~~

摘　　要：本文运用LA-ICP-MS锆石U-Pb定年法对新疆阿奇山岩体进行了测定,获得年龄为269.5±1.6 Ma^272.1±1.3 Ma,表明阿奇山岩体为晚二叠世。岩石的Sr、Nd、Pb同位素分析表明,该岩体有较低的锶同位素初始比值[n(87Sr)/n(86Sr)]i(0.7044~0.7055)、正εNd(t)值(0.48~3.66)及较为年轻的Nd同位素两阶段模式年龄t2DMC(741~1090 Ma),表明其源岩与亏损地幔有关,而在Pb同位素n(207Pb)/n(204Pb)-n(206Pb)/n(204Pb)构造模式演化图解中,又显示其物质来源与壳幔相互作用有关。综合岩体岩石地球化学特征、前人研究成果及该区大地构造背景,分析认为阿奇山岩体的形成是地幔柱活动背景下壳幔相互作用过程的产物。阿奇山岩体位于新疆北部,属于中亚造山带的一部分,在晚二叠世,整个新疆北部已经进入后造山阶段,且晚古生代时期板块俯冲已经结束。但后造山岩浆形成必然需要新的动力及热源,而幔源岩浆的底侵不仅可以为后造山岩浆活动提供热源,还提供了大量物源。因此在区域性伸展构造环境下,由于壳幔相互作用强烈,来自深部的地幔柱幔源岩浆底侵,带来的热源诱发较年轻的地壳物质部分熔融,同时有部分幔源物质的混染,从而使阿奇山岩体花岗岩物源具有地幔和地壳双重特征。Objectives: Aqishan pluton is located in Shanshan county,Turpan region,Xinjiang province. In geotectonic position,It is located near the boundary between the Kazakh-Zhunge plate and the Tarim plate,and is inclined to the Tarim plate. By collecting the data from previous studies,some profiles have been performed systematically to reveal the characteristics of mineralogy,petrology and lithogeochemistry of Aqishan pluton. While very fewer work on high precision isotopic age have been done,and the study on Sr,Nd,Pb isotopes have not been carried out.Methods: We use the methods of high precision isotopic age dating which called LA-ICP-MS Zircon U-Pb age dating to determine the formation age of Aqishan pluton;On the other hand,we use Sr-Nd-Pb isotope geochemical tracer technique to synthetical analyse the genesis of Aqishan pluton.Results: The result of LA-ICP-MS zircon U-Pb dating shows that the age of Aqishan Pluton is 269.5±1.6 Ma ~272.1 ± 1. 3 Ma,indicating that the Aqishan pluton formed in Late Permian. As for the Sr-Nd-Pb isotope compositions,the rocks have low initial ratio of strontium isotope [n(87Sr)/n(86Sr)]i( 0.70442 ~ 0.70553),positive εNd(t) values (0. 48 ~ 3. 66) and relatively juvenile t2DMC( 741 ~ 1090 Ma). The Sr-Nd isotope compositions suggest that their primitive magma was most possibly derived from juvenile crust with variable involvement of depleted mantle derived magma,while in the Pb tectonic framework diagram,the material source is also related to the crust-mantle interaction. In combination with the characteristics of lithogeochemistry,previous research results and tectonic background,we analyzed that Aqishan pluton is the product of crust-mantle interaction under the background of mantle plume activity. Aqishan pluton is located in the northern Xinjiang,belongs to the part of the Central Asian orogenic belt,in Late Permian,the entire northern Xinjiang has entered to post-orogenic satge,and the late Paleozoic plate subduction dynamics system has ended,while the formation of post-orogenic ma

关 键 词：LA-ICP-MS锆石U-PB年龄 Sr、Nd、Pb同位素 岩石成因 阿奇山岩体 

分 类 号：P597[天文地球—地球化学] P581[天文地球—地质学]