南阿尔金木纳布拉克地区石英闪长岩的成因:来自地球化学特征、锆石U-Pb定年和Lu-Hf同位素组成的制约  

Origin of quartz diorite in the Munabulake area, South Altyn Tagh: constraints from geochemical characteristics, zircon U-Pb dating and Lu-Hf isotopic composition

作　　者：高慧 曹玉亭 刘良[3] 王超[3] 康磊[3] 杨文强[3] 陈晓宏[5] GAO Hui;CAO Yuting;LIU Liang;WANG Chao;KANG Lei;YANG Wenqiang;CHEN Xiaohong(Shandong Provincial Key Laboratory of Depositional Mineralization&Sedimentary Minerals,College of Earth Science&Engineering,Shandong University of Science and Technology,Qingdao 266590;Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069;Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029;Gas-field development department,CNPC Qinghai Oilfield Company,Dunhang,Gansu,736202)

机构地区：[1]山东省沉积成矿作用与沉积矿产重点实验室,山东科技大学地球科学与工程学院,山东青岛266590 [2]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [3]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [4]地球与行星物理院重点实验室,中国科学院地质与地球物理研究所,北京100029 [5]青海油田气田开发处,甘肃敦煌736202

出　　处：《地质学报》2020年第8期2262-2278,共17页Acta Geologica Sinica

基　　金：山东省自然科学基金(ZR2019BD046);国家自然科学基金(41872053,41602052);自然资源部深地动力学重点实验室开放课题基金(J1901-16);西北大学大陆动力学国家重点实验室开放课题基金(17LCD07);山东科技大学科研创新团队支持计划(2015TDJH101)等项目资助的成果。

摘　　要：本文对南阿尔金木纳布拉克地区西侧出露在巴什库尔干岩群的石英闪长岩体进行了详细的岩石学、全岩地球化学、锆石年代学和Lu-Hf同位素分析研究。全岩地球化学显示,石英闪长岩的SiO2=55.94%~57.38%,具有高的Na2O/K2O=1.19~1.60比值、准铝质(A/CNK=0.92~0.95)的特征。稀土元素配分图上,所有样品显示弱或无Eu负异常,轻稀土富集和重稀土相对亏损;在原始地幔标准化微量元素蛛网图上,大部分样品相对富集Rb、Ba、K等大离子亲石元素,相对亏损Nb、Ta、P、Ti等高场强元素,总体显示壳源型高钾钙碱性-钙碱性系列的准铝质I型花岗岩特征。CL阴极发光图像显示,该石英闪长岩中的锆石晶体多为长柱状,自形程度较好,具有清晰的韵律环带结构,利用LA-ICP-MS进行锆石U-Pb定年分析,获得其年龄为455.5±1.3Ma,结合锆石的CL图像内部结构特征,推断该年龄为石英闪长岩的结晶年龄。该年龄与南阿尔金高压-超高压岩石的高压麻粒岩相退变质年龄一致,且与南阿尔金早古生代第三期岩浆活动时间(460~451Ma)一致。锆石Hf同位素研究获得该岩石的两阶段模式年龄(1512~1823Ma)和Hf同位素组成[εHf(t)=-6.29^-1.35]与南阿尔金同期的~450Ma的早古生代花岗岩一致[tDM2=1331~1789 Ma,εHf(t)=-8.8^-0.4],表明二者源岩的源区具有相似性,主要来自于中元古-古元古地壳物质的重熔再造。在源岩判别图解上,所有样本均落在玄武岩源区附近,推断该石英闪长岩为下地壳玄武岩部分熔融形成。此外,研究区内出露有与该石英闪长岩同时期的超镁铁质岩石,且样品的某些地球化学特征值介于地幔和地壳平均值之间,显示其形成过程中应有幔源岩浆的混入。综合上述研究,推断南阿尔金木纳布拉克地区的石英闪长岩应为南阿尔金俯冲陆壳在折返过程中,由于压力降低导致下地壳玄武岩发生部分熔融并与地幔物质发生混合,后侵入地壳�The article mainly focusses on the petrology, geochemistry, zircon chronology and Lu-Hf isotope analysis of the quartz diorite that is exposed in the Bashikourgan rock group in the Munabulake area on the west side of the South Altyn Tagh. Whole rock geochemical research indicates that the quartz diorite has SiO2 content of 55.94%~57.38%, exhibits the characteristics of high ratio of Na2O/K2O=1.19~1.60 and quasi-aluminium(A/CNK=0.92~0.95). On the REE partition diagram, all samples show weak or no obvious Eu anomaly, enriched LREE pattern and defected HREE pattern. On the primitive mantle-normalized spider diagram, samples are relatively enriched in large ion lithophile elements(LILE), such as Rb, Th and K, and depleted in high field strength elements(HFSE), such as Nb, Ta, Sr, P and Ti, showing the characteristics of quasi-aluminous I-type granites of crustal high-K calc-alkaline to calc-alkaline series. The zircon crystals in the quartz diorite are euhedral and mostly show long columnar shape with clear oscillatory zones. Zircon U-Pb dating by LA-ICP-MS obtains the age of 455.5±1.3 Ma, which is inferred to represent the formation age of quartz diorite based on the internal structure of CL image of zircon. This age is identical to the high-pressure granulite facies retrograde metamorphic age of HP/UHP rocks from the South Altyn Tagh, and is also identical to the third stage of the magmatism(460~451 Ma) in early Paleozoic in the South AltynTagh. All spots of zircons have εHf(t)=-6.29^-1.35 and TDMC=1512~1823 Ma, which is similar to early Paleozoic granite of the Southern AltynTagh(TDMC=1331~1789 Ma, εHf(t)=-8.8^-0.4), suggesting that they were derived from the consistent source rock, which was accreted in Middle Mesoproterozoic-Paleoproterozoic. According to the geochemical characteristics, the quartz diorite was inferred to have formed by partial melting of the basalt in the lower crust, with mantle magma mixed in during the formation process. Based on the results of our studies we conclude that the quartz dior

关 键 词：木纳布拉克地区 石英闪长岩 高压-超高压变质 锆石U-PB定年 锆石Lu-Hf同位素特征 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]