东昆仑五龙沟晚二叠世花岗闪长岩LA-ICP-MS锆石U-Pb定年、岩石成因及意义  

Zircon U-Pb geochronology,petrogenesis and implication of the Later Permian granodiorite from the Wulonggou Area in East Kunlun,Qinhai Province

作　　者：罗明非[1,2] 莫宣学[1,2] 喻学惠[1,2] 李小伟[1,2] 黄雄飞[1,2] 

机构地区：[1]地质过程与矿产资源国家重点实验室 [2]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2015年第5期182-195,共14页Earth Science Frontiers

基　　金：中国地质调查局工作项目(1212011121260);国家自然科学基金项目(41403028);中国博士后科学基金资助项目(2014M550081)

摘　　要：报道了东昆仑东段五龙沟岩体的锆石U-Pb年代学、全岩和痕量元素地球化学、Sr-Nd同位素和原位锆石Hf同位素数据。五龙沟岩体的LA-ICP-MS锆石U-Pb定年表明花岗闪长岩主要侵位于260 Ma左右。花岗闪长岩具有适中的SiO2、高Al2O3和全碱含量,属于中钾钙碱性弱过铝质系列。样品富集LREE,大离子亲石元素(LILE),亏损高场强元素(HFSE),具有陆缘弧花岗岩的特征。此外,花岗闪长岩具有弱的负Eu异常(δEu=0.8~1.0),高Sr((377~484)×10-6),低Y((8.7~17.5)×10-6)和Yb((0.89~1.57)×10-6),类似于埃达克质岩石的地球化学特征。岩石具有较均一(87Sr/86Sr)i值(0.709 1~0.707 6),较低的全岩εNd(t)值(-4.3^-5.3)和古老的Nd模式年龄T2DM(1.6~1.7Ga)。原位锆石Hf同位素显示εHf(t)值介于0.6^-3.5,对应二阶段模式年龄T2DM(1.3~1.5Ga)。上述地球化学特征说明花岗闪长质岩浆是由古老的基性下地壳部分熔融而成,其形成深度在30~40km。岩体中出露的同生成基性岩墙指示该时期有幔源岩浆活动,部分熔融作用可能与岩浆底侵作用相关。因此,结合区域地质研究,我们认为晚二叠世五龙沟花岗闪长岩形成于活动大陆边缘的局部伸展环境,这种背景可能响应了布青山—阿尼玛卿洋洋壳北向俯冲过程中俯冲极性的突变。In this paper, we report the zircon U-Pb geochronology, whole-rock major elements and trace elements, Sr-Nd isotopic compositions and in situ zircon Lu-Hf isotopic date for the Wulonggou pluton in the eastern segment of East Kunlun. The LA-ICP-MS U-Pb zircon dating result has shown that the Wulonggou pluton was emplaced around 260 Ma. The granodiorite has moderate SiO2 concentrations, high Al2O3 and total alkalis contents, which can be classified into the medium K calc-alkaline and weakly peraluminous series. The rock samples display marked enrichment in LILE, depletion in HFSE, showing affinities similar to continental arc granites. In addition, the granodiorite has weakly negative Eu anomalies （εEu =0. 8- 1.0）, high Sr contents （（377 - 484） × 10 ^-6 ） and low Y （ （8. 7 - 17.5） × 10^-6 ） and Yb （（0. 89 - 1.57） × 10^-6 ） abundances, displaying geochemical characteristics similar to those of adakitic rock. The studied rocks have uniform initial 87 Sr/86 Sr （0. 7091 -0. 7076）, and relatively low whole-rock SNa （t） values （--4. 3---5.3）, corresponding to the ancient Nd model ages of （1.6- 1.7 Ga）. In situ zircon Lu-Hf isotopic data have shown that the egf（t） values range from 0. 6 to -- 3.5, corresponding to the two-stage models ages of 1.3 - 1.5 Ga. The geochemical features mentioned above have demonstrated that these granodiorites were derived from partial melting of the ancient mafic lower crust, with depths varying from 30 to 40 km. The occurrence of syn-magmatic mafic dikes among these granodiorites indicates the presence of the mantle-derived magmas, and the trigger of partial melting is probably related to the continental magmatic underplating. Consequently, in combination with the regional geology, we argue that the Permian Wulonggou pluton formed in the active continental margin, along with local extension. This geological background may be in response to the abrupt change of subduction polarity of the northward subducting Buqingshan-A＇nyemaqen oceanic c

关 键 词：东昆仑 晚二叠世 花岗闪长岩 埃达克质 岩浆底侵 俯冲环境 

分 类 号：P588.12[天文地球—岩石学]