班公湖-怒江缝合带西段阿翁错地区中酸性侵入岩的成因及其对区域构造演化的指示  

Petrogenesis of Intermediate-Acid Intrusive Rocks in Awengcuo Area in the West Segment of the Bangongco-Nujiang Suture, Tibet, and its Implications on the Regional Tectonic Evolution

作　　者：雷传扬[1,2] 吴建亮[2] 尹显科[2] 刘文[2] 王波[2] 李威[1,2] 袁华云 张伟[2] 尹滔[2] 裴亚伦[2] LEI Chuanyang;WU Jianliang;YIN Xianke;LIU Wen;WANG Bo;LI Wei;YUAN Huayun;ZHANG Wei;YIN Tao;PEI Yalun(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan,China;Geological Survey of Sichuan Province,Chengdu 610081,Sichuan,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]四川省地质调查院,四川成都610081

出　　处：《大地构造与成矿学》2019年第1期168-185,共18页Geotectonica et Metallogenia

基　　金：中国地质调查局班公湖-怒江成矿带铜多金属矿资源基地调查项目(DD20160026)资助

摘　　要：班公湖-怒江缝合带西段出露大量中酸性侵入岩,为特提斯洋俯冲、拉萨地块与羌塘地块碰撞造山过程中岩浆响应的重要组成部分。本文对该缝合带西段阿翁错地区的闪长岩、花岗闪长岩和花岗岩进行了详细的岩石地球化学和锆石U-Pb年代学研究。锆石LA-ICP-MS U-Pb定年结果表明闪长岩、花岗闪长岩、花岗岩成岩年龄分别为119.3±1.8 Ma、114.7±1.4 Ma和103.2±1.3 Ma。岩石地球化学特征显示中酸性侵入岩属高钾钙碱性系列,具准铝质-弱过铝质I型花岗岩特征;其LREE分馏程度较高,而HREE近于平坦,存在Eu负异常;富集Rb、La等大离子亲石元素和Th、Zr、Hf等高场强元素,亏损Nb、Ta、P、Ti等高场强元素,具有岛弧岩浆岩的特征。研究结果表明在早白垩世晚期(103.0±1.3 Ma)班公湖-怒江特提斯洋壳仍在向北俯冲于南羌塘地块之下,随着俯冲深度增加,大洋板片发生大规模脱水,释放的流体交代地幔楔并引发其部分熔融,产生的幔源岩浆向上运移,与下地壳物质不同比例混合形成了闪长岩和花岗闪长岩;而花岗岩主要由古老下地壳物质部分熔融形成,并有少量地幔物质的参与。Numerous intermediate-acid intrusions outcrop in the western segment of the Bangongco-Nujiang suture zone,which are possibly results of the subduction of the Tethys Ocean and the orogenic process of the Lhasa and Qiangtang Blocks.Detailed geochemical and zircon U-Pb isotopic analyses have been carried out on the diorites,granodiorite and granite in the western segment of this suture zone.According to the LA-ICP-MS zircon U-Pb dating results,the ages of the three kinds of intrusions are 119.3±1.8 Ma,114.7±1.4 Ma and 103.2±1.3 Ma,respectively.The intrusive rocks are high-potassium calc-alkaline and metaluminous to weakly peraluminous,showing characteristics of I-type granite.The chondrite normalized REE patterns are characterized by significant enrichment and fractionation of LREE,relatively flat HREE patterns and negative Eu anomalies.The primitive mantle normalized trace element spider diagrams show relative enrichment of large ion lithophile elements,such as Rb,and high field strength elements,such as Th,Zr,and Hf,with depletion of Nb,Ta,P and Ti.These geochemical characteristics are similar to those of island arc magmatic rocks,indicating that the Bangongco-Nujiang Tethyan Oceanic Plate subducted northward under the South Qiangtang Block during the Early Cretaceous(103.2±1.3 Ma).Dehydration of the subducting oceanic plate yielded fluids that metasomatized the mantle wedge,and caused the partial melting of the mantle.The mixing of the mantle-derived magma with melts of the lower crustal basic rocks formed the parental magma of the diorite and granodiorite in the study area,while the granite was likely formed from partial melting of the ancient lower crust with minor mantle materials.

关 键 词：西藏 班公湖-怒江缝合带 阿翁错地区 锆石U-PB年龄 岩石成因 岩浆源区 构造演化 

分 类 号：P581[天文地球—岩石学] P54[天文地球—地质学]