伊犁盆地南缘琼博拉二长花岗岩锆石年代学及形成动力学机制  

The Zircon U-Pb geochronology and dynamics mechanism for the formation of monzonitic granite in the Qiongbola area, south of Yili basin

作　　者：李平[1] 刘红旭[1] 丁波[1] 田明明[1] LI Ping;LIU Hongxu;DING Bo;TIAN Mingming(Beijing Research Institute of Uranium Geology,Beijing 100029,China)

机构地区：[1]核工业北京地质研究院,北京100029

出　　处：《中国地质》2018年第4期720-739,共20页Geology in China

基　　金：国家重点基础研究发展计划"973"项目"典型产铀盆地成矿机理与成矿模式研究"(2015CB453004);中国地质调查局"塔里木盆地北缘库车坳陷西段铀矿资源调查评价"项目(DD2016013628)联合资助~~

摘　　要：西天山造山带内琼博拉地区的长条状岩体位于伊犁盆地南缘,由二长花岗岩组成。为厘定该二长花岗岩的形成机制,本文对该二长花岗岩进行了详细的锆石U-Pb年代学、主量元素、微量元素以及Sr-Nd-Pb同位素研究。LA-ICP-MS锆石年代学研究揭示出琼博拉地区二长花岗岩成岩年龄为(330.5±2.2)Ma、(339.7±2.2)Ma、(351.2±3.0)Ma,为早中石炭世花岗岩,比伊犁盆地511矿床含矿砂体的U-Pb同位素等时线年龄(308±26Ma)老,表明该二长花岗岩体可能是该含矿砂体的一部分物质来源。岩石主量元素、微量元素和Sr-Nd-Pb同位素测试结果揭示该二长花岗岩具有以下特征:(1)SiO_2(70.15%~73.38%)含量高,碱质(K_2O+Na_2O含量为6.32%~7.88%)含量较高,A/CNK(0.82~1.03)较高,表明二长花岗岩为准铝质岩石,属于高钾钙碱性系列;(2)LREE(50.19×10^(-6)~87.92×10^(-6))相对富集,HREE(9.44×10^(-6)~12.08×10^(-6))相对亏损,无明显Eu异常(δEu为0.71~0.97);(3)富集Rb、Th、K、Pb和Sr等大离子亲石元素,相对亏损Nb、Ta、Zr、P和Ti等高场强元素;(4)初始锶同位素比值为0.7050~0.7082,143Nd/144Nd值为0.512217~0.512254,ε_(Nd)(t)为0.3~1.0,Nd模式年龄为1010~1098 Ma。二长花岗岩的Sr、Nd、Pb同位素组成表明该岩石是由幔源玄武质岩浆与地壳重熔形成的硅铝质岩浆混染形成。结合区域构造演化,本文认为二长花岗岩形成于板块的同碰撞构造环境。Located in the south of Yili basin,the Western Tianshan Orogen belt played an essential provenance role in the formation of Yili basin.This paper focused on the dominant monzonitic granites of Qiongbola area,which is situated on the northern margin of Western Tianshan belt.The authors investigated their U-Pb geochronology by using zircon and geochemistry.These granites are Early Carboniferous intrusions,which mainly include three stages,which are(351.2±3.0)Ma,(339.7±2.2)Ma,and(330.5±2.2)Ma,respectively,according to the LA-ICP-MS U-Pb dating results of zircons.The whole-rock U-Pb dating of ore-bearing sandstone of 511 U deposit yielded an isochron age of 308±26Ma,suggesting that these granites were probably the main provenance for orebearing sandstone.The SiO2 content of these granites varies from 70.15%to 73.38%,the K2O+Na2O values vary from 6.32%to 7.88%,and the A/CNK ratios vary from 0.82 to 1.03,suggesting that these intrusions are high-K calc-alkaline granites.The LREE values are from 50.19×10-6 to 87.92×10-6,suggesting relatively more enriched than HREE which are 9.44×10-6 to 12.08×10-6,withδEu being commonly 0.71 to 0.97.In addition,these granites are commonly rich in Rb,Th,K,Pb,and Sr and depleted in Nb,Ta,Zr,P,and Ti.The Sr isotope ratios range from 0.7050 to 0.7082,the 143Nd/144Nd ratios vary from 0.512217 to 0.512254,and theεNd(t)vary from 0.3 to 1.0,with model ages being from 1010 to 1098Ma.These geochemical results highly suggest that these intrusions were the mixture of mantle-derived basaltic and crustal molten magma,and were formed in the syn-collision tectonic environment.

关 键 词：二长花岗岩 锆石年代学 SR-ND-PB同位素 琼博拉 西天山 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]