东昆仑浪麦滩地区A型花岗岩年代学、地球化学特征及其地质意义  

Geochronology, geochemical characteristics and geological significance of A-type granite from the Langmaitan area, East Kunlun

作　　者：李金超[1] 国显正 孔会磊[1] 姚学钢 贾群子[1] LI Jinchao;GUO Xianzheng;KONG Huilei;YAO Xuegang;JIA Qunzi(Xi’an Center of Geological Survey,CGS,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposit,MNR,Xi'an,Shaanxi 710054,China;School of Resources ancl Environmental Engineering Hefei University of Technology,Hefei,Anhui 230009,China)

机构地区：[1]中国地质调查局西安地质调查中心.自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [2]合肥工业大学资源与环境工程学院,安徽合肥230009

出　　处：《地质学报》2021年第5期1508-1522,共15页Acta Geologica Sinica

基　　金：第二次青藏高原综合科学考察研究项目(编号2019QZKK0801);中国地质调查局项目(编号DD20190143,DD20160013)资助的成果。

摘　　要：东昆仑造山带出露大面积的花岗岩,是研究岩浆活动的天然实验室,晚三叠世A型花岗岩为该区构造演化提供了新的约束。本文通过对东昆仑浪麦滩地区出露的正长花岗岩开展岩相学、锆石U-Pb定年、Hf同位素及地球化学研究,以期限定其形成时代,探讨岩石成因,并为区域构造岩浆演化提供依据。正长花岗岩由正长石、条纹长石、斜长石、石英和少量黑云母等矿物组成。LA-ICP-MS锆石U-Pb年龄为231.5±1.7Ma,形成于晚三叠世。岩石地球化学具有高硅富铝特征,SiO_(2)含量为72.36%~74.58%,Al2O3含量为12.76%~12.89%,相对富钾贫钠,K_(2)O、Na_(2)O含量分别为4.43%~4.96%、4.0%~4.25%,低MgO、TiO_(2),富集Rb、K等大离子亲石元素,强烈亏损Ba、Nb、Ta、P、Ti等高场强元素,具有明显的负铕异常(δEu=0.040~0.08),表明为A型花岗岩。Mg#介于0.40~0.43之间,εHf(t)值介于+2.05~+7.53之间,二阶段Hf模式年龄TDM2为782~1132 Ma,指示源区有幔源岩浆物质的参与。综合分析表明,在后碰撞伸展背景下由于幔源岩浆底侵,新生地壳部分熔融并混入幔源物质,最终形成浪麦滩地区A型花岗岩。East Kunlun contains large areas of intermediate-acid intrusive rocks, providing a natural laboratory for the study of magmatism, and the Late Triassic A-type granites can provide new constraints for the tectonic evolution in this area. In this paper, we present a detailed investigation of zircon U-Pb dating, whole rock geochemistry and Hf isotopes of the Langmaitan syenogranite in the eastern segment of East Kunlun, in order to identify the chronology and petrogenesis of rocks, and provide a basis data for the evolution of regional tectonics. Syenogranite consists mainly of orthoclase, perthite, plagioclase, quartz, and a small amount of biotite. The zircon U-Pb dating yields an age of 231.5±1.7 Ma, indicating its emplacement in Late Triassic. The syenograniteis geochemically characterized by high SiO_(2)(72.36%~74.58%) and rich Al2O3(12.76%~12.89%);is relatively rich in K_(2)O(7.52%~7.89%), but poor in Na_(2)O(4.0%~4.25%), low in MgO and TiO_(2);enriched in large ion lithophilic elements Rb, K, etc., depleted in high field strength elements such as Ba, Nb, Ta, P, Ti, and displays significantly negative europium anomalies(δEu=0.04~0.08). All these characteristics indicate that they are A-type granites. Mg# is between 0.40 and 0.43, the εHf(t) value is between +2.05 and +7.53, and TDM2 ages between 782 Ma and 1132 Ma, indicating that the syenogranite involvement of mantle components in petrogenesis. Based on the comprehensive regional geology and the characteristics, it is concluded that the Langmaitan A-type granite formed by partial melting of juvenile crust and mixed with mantle-derived materials in post-collision extensional environment.

关 键 词：正长花岗岩 锆石U-PB定年 地球化学 LU-HF同位素 东昆仑 

分 类 号：P588.121[天文地球—岩石学]