摘要
本文对青海南山构造带西段黑马河花岗杂岩体中的石英闪长岩和花岗闪长岩以及花岗闪长岩中的暗色微粒包体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb年代学研究。结果表明,花岗闪长岩及暗色微粒包体的结晶年龄分别为244.4±1.1 Ma和243.0±1.2 Ma,表明岩体形成于中三叠世早期。石英闪长岩和花岗闪长岩为准铝质高钾钙碱性系列,暗色微粒包体为高钾钙碱性—钾玄岩系列,稀土元素配分曲线均具有轻重稀土明显分异的右倾特征,具弱负Eu异常(δEu=0.65~0.83),富集大离子亲石元素(Cs、Rb、Th、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常。岩相学和岩石地球化学特征指示黑马河花岗杂岩体具壳幔岩浆混合特征,形成于活动大陆边缘的俯冲环境,石英闪长岩为受俯冲流体交代的地幔楔部分熔融产生的基性岩浆演化的产物,花岗闪长岩则源自壳源岩浆与少量幔源岩浆的混合。黑马河花岗杂岩体是中三叠世早期宗务隆洋向南俯冲消减的岩浆记录。
Objectives：As a granitic pluton in the west part of the Qinghai’nanshan tectonic belt，the Heimahe granitic pluton are mainly composed of granodiorite, quartz diorite, diorite and gabbro. The formation age and geochemical affinity of those rocks play a key role for investigating the transitional relation between the west Qinling and the Qilian orogenic belts in Paleozoic Tethys evolution stage． Methods：In this paper，a detailed study of LA-ICP-MS zircon U-Pb dating，petrology and geochemistry characteristics was carried out for quartz diorite，granodiorite and mafic microgranular enclaves from the Heimahe granitic pluton． Results：The LA-ICP-MS zircon U-Pb ages of the granodiorite and MMEs are 244.4 ± 1.1 Ma and 243.0 ± 1.2 Ma，respectively，indicating that the Heimahe granitic pluton formed in early Middle Triassic．The whole rock geochemical data show that quartz diorite and granodiorite belong to the metaluminous high-K calc-alkaline series and MMEs are high-K calc-alkaline to alkaline series．The REE patterns display rightward incline and weak negative Eu anomalies（δEu = 0.65 ~ 0.83）．The trace element geochemistry is evidently characterized by positive anomaly of LILEs（e.g. Cs，Rb，Th，K）and Pb，negative anomaly of HFSE（e.g. Nb，Ta，Ti）and P，Ba． Conclusions：The petrographic and geochemical characteristics of the Heimahe granitic pluton imply a closely subduction related origin at active continental margin arcs，with crust—mantle mixing characteristics．The mafic magma was derived from partial melting of the mantle wedge which was metasomatized by hydrous fluids from subduction slab dehydration. Then the quartz diorite originated from crystallization differentiation of mantle source magma，and the granodiorite originated from crust sourced magma mixing some mantle sourced magma．Connecting with the predecessors research results，it can be supposed that the petrogenesis of the Heimahe granitic pluton may be related to the southward subduction of Zongwulong Oceanic crust during the early Middle Triassic．
作者
张永明
裴先治
李佐臣
李瑞保
刘成军
裴磊
陈有炘
陈国超
王盟
ZHANG Yongming PEI Xianzhi LI Zuochen LI Ruibao LIU Chengjun PEI kei CHEN Youxin CHEN Guochao WANG Meng(Key Laboratory of Western China＇ s Mineral Resources and Geological Engineering, Ministry of Education, Key Laboratory for the study of Focused Magmatism and Giant Ore Deposits ,MLR ,Faculty of Earth Science and Resources Chang＇ an University,Xi＇ an, 710054 Faculty of Resources and Environmental Engineering, Shandong University of Technology, Zibo, Shandong, 255049 China University of Geosciences ,Beijing, 100083 Nanyang lnstitutte of Technology, Nanyang, Henan, 473000)
出处
《地质论评》
CAS
CSCD
北大核心
2017年第4期1079-1101,共23页
Geological Review
基金
国家自然科学基金资助项目(编号:41472191、41502191、41172186)
中国地质调查局地质调查项目(编号:12120114041201、12120114018219)
中央高校基本科研业务费专项资金项目(编号:CHD2011TD020、2013G1271091、2013G1271092)的成果~~
关键词
青海南山
黑马河花岗杂岩体
锆石U-PB年龄
岩石成因
构造环境
Qinghai’nanshan tectonic belt
Heimahe granitic pluton
LA-ICP-MS zircon U-Pb dating
petrogensis
tectonic setting
