西藏中拉萨地块晚侏罗世许如错花岗岩地球化学与岩石成因  

Geochemistry and petrogenesis of the Late Jurassic Xuru Tso batholith in central Lhasa Terrane

作　　者：闫晶晶[1] 赵志丹[1] 刘栋[1] 王珍珍[1] 唐演[1] YAN JingJing ZHAO ZhiDan LIU Dong WANG ZhenZhen TANG Yan(State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China)

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

出　　处：《岩石学报》2017年第8期2437-2453,共17页Acta Petrologica Sinica

基　　金：国家重点研发计划(2016YFC0600304);国家“973”项目(2015CB452604);国家自然科学基金项目(41273044、41225006);中国地质调查局工作项目(1212011121260、1212011121066);长江学者和创新团队发展计划(IRT1083)联合资助

摘　　要：西藏中部拉萨地块晚侏罗世花岗岩的岩石成因与源区性质目前尚未得到很好约束。本文报道了中部拉萨地块西段许如错岩体的寄主花岗岩和闪长质包体的锆石U-Pb年龄、元素地球化学和锆石Hf同位素成分。许如错岩体寄主花岗岩年龄为155.1±0.7Ma,闪长质包体与寄主花岗岩同期(155.7±0.7Ma)形成。寄主花岗岩属I型偏铝质-弱过铝质高钾钙碱性系列岩石,富集Rb、K等大离子亲石元素和轻稀土元素,亏损Nb、Ta、P、Ti等高场强元素,锆石εHf(t)值(-16.6^-6.6)指示其可能来源于拉萨地块古老下地壳物质的重熔作用。闪长质包体为准铝质钙碱性系列,锆石εHf(t)值(-8.9^-3.8)具有总体为负但明显高于寄主花岗岩εHf(t)值的特征,表明这些闪长质包体代表了幔源物质组成的加入。许如错晚侏罗世花岗岩可能形成于班公湖-怒江特提斯洋洋壳在中晚侏罗世向南俯冲于拉萨地块之下,引起幔源物质与中部拉萨地块古老基底重熔所产生的酸性岩浆发生岩浆混合作用形成的。The Late Jurassic magmatism is spreading in the central Lhasa subterrane,but their petrogenesis remains poorly constrained. This study presents new zircon U-Pb age,whole rock geochemistry,and zircon Hf isotopic data for the host granite and dioritic enclaves from the Xuru Tso area. The zircon dating for the host granite yields U-Pb age of 155. 1 ± 0. 7Ma,which is identical to that of the dioritic enclave（155. 7 ± 0. 7Ma）. The host rocks are metaluminous to slightly peraluminous and high K calc-alkaline I-type granites,showing enrichment of large ion lithophile elements and light rare earth elements relative to high field strength elements. Their negative zircon εHf（t） values（-16. 6 ^-6. 6） indicate that they were derived from antaxis of ancient Lhasa terrane crust. The dioritic enclaves are metaluminous calc-alkaline and exhibit overall negative but significantly higher zircon εHf（t） values（-8. 9 ^-3. 8） in comparison with the host granites,suggesting that these enclaves may document the input from mantle lithosphere. These observations indicate that the Late Jurassic granitoids from Xuru Tso were formed by the magma mixing between mantle-derived melts and crust-derived silicic melts originating from ancient crust beneath central Lhasa subterrane,and can be best explained as reflecting the southward subduction of Bangong-Nujiang Neo-Tethyan oceanic seafloor.

关 键 词：地球化学 锆石U-Pb-Hf 许如错花岗岩 中部拉萨地块 青藏高原 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]