摘要
青海南山构造带是衔接宗务隆构造带、南祁连构造带和西秦岭造山带的重要结合带。沟后岩浆杂岩体位于青海南山构造带东段,主要由辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩组成。本文对沟后岩浆杂岩体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb同位素年代学研究。结果表明,辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩及暗色微粒包体的结晶年龄分别为248.8±2.6 Ma、243.2±2.1 Ma、243.1±0.9 Ma、244.0±2.1 Ma和249±3 Ma。辉长岩富铁、镁,贫碱;辉长闪长岩高铝、富钙和钠,二者均为钙碱性岩类。石英闪长岩和花岗闪长岩为准铝-弱过铝质高钾钙碱性岩,暗色微粒包体属钙碱性-碱性岩系列。不同岩石类型均表现为富集大离子亲石元素(Cs、Rb、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常;稀土元素配分曲线均具有轻重稀土分异的右倾特征,具弱-中等负Eu异常。岩相学和岩石地球化学特征表明沟后岩浆杂岩体具壳幔岩浆混合特征,暗示其可能形成于由俯冲流体交代地幔楔部分熔融的幔源岩浆底侵作用下的构造环境。辉长岩为幔源岩浆经分离结晶的产物,辉长闪长岩为幔源岩浆经分异演化并混染少量壳源岩浆的产物;中基性岩浆与壳源中酸性岩浆发生混合并经历一定的分异演化过程形成了石英闪长岩和花岗闪长岩。结合区域地质资料分析认为,沟后岩浆杂岩体可能代表了研究区早三叠世晚期-中三叠世早期宗务隆洋向南消减作用相关的构造岩浆事件。
The Qinghai Nanshan tectonic belt, situated in the northern margin of the Gonghe Basin, is the conjunction area among the West Qinling orogenic belt, South Qilian tectonic belt and Zongwulong tectonic belt. As a magmatic complex in the east part of the Qinghai Nanshan tectonic zone, the Gouhou complex consists of gabbro, gabbro-diorite, quartz diorite, and granodiorite. In this paper, a detailed study of LA-ICP-MS zircon U-Pb geochronology, petrology and geochemistry were carried out on the Gouhou complex. LA-ICP-MS zircon U-Pb ages of the gabbro, gabbro-diorite, quartz diorite, granodiorite and MMEs are 248.8±2.6 Ma, 243.2±2.1 Ma, 243.1±0.9 Ma, 244.0±2.1 Ma and 249±3 Ma, respectively. Geochemically, the gabbros have low Na2O＋K2O, but high Fe2O3T and MgO contents, and the gabbro-diorites are enriched in CaO, Al2O3 and Na2O, overall belonging to the calc-alkaline series. The quartz diorite and granodiorite are metaluminous to weak peraluminous and high-K calc-alkaline, whereas the enclaves are of high-K calc-alkaline to alkaline series. All the samples are evidently enriched in LILEs （Cs, Rb, K） and Pb, and depleted in HFSEs （Nb, Ta, Ti） and P, Ba. The REE patterns are right-dippling lines with weak to moderate negative Eu anomalies. The above petrographic and geochemical characteristics of the rocks suggest that mixing of mantle- and crust-derived magmas played an important role in the generation of the Gouhou complex. Partial melting of the wedge mantle, which was metasomatized by hydrous fluids from the subducted slab, generated the primitive basaltic magma. The gabbros were produced by fractional crystallization of mantle-derived primitive magma. The gabbro-diorites were formed through a more complicated process that involves fractional crystallization of the primitive basaltic magma and contamination of crustal material. The quartz diorites and granodiorites crystallized from a hybrid magma formed by mixing of the intermediate-basic magma and intermediate-felsic magma. Considering the regional tectonic evolution, we propose that the Gouhou complex was related to the southward subduction of the Zongwulong oceanic crust from the late stage of Early Triassic to the early stage of Middle Triassic.
作者
张永明
裴先治
李佐臣
李瑞保
刘成军
裴磊
陈有炘
王盟
陈国超
ZHANG Yongming PEI Xianzhi LI Zuochen LI Ruibao LIU Chengjun PEI Lei CHEN Youxin WANG Meng CHEN Guochao(MOE Key Laboratory of Western China＇s Mineral Resources and Geological Engineering, MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, Faculty of Earth Science and Resources, Chang＇an University, Xi＇an 710054, Shaanxi, China Faculty of Resources and Environmental Engineering, Shandong University of Technology, Zibo 255049, Shandong, China School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China School of Civil Engineeringy, Nanyang Institutte of Technology, Nanyang 473000, Henan, China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2017年第5期908-932,共25页
Geotectonica et Metallogenia
基金
国家自然科学基金(41472191
41502191
41172186)
中国地质调查局地质调查项目(12120114041201
12120114018219)
中央高校基本科研业务费专项资金(CHD2011TD020
2013G1271091
2013G1271092)联合资助
关键词
青海南山
西秦岭北缘
沟后岩浆杂岩体
锆石U-PB定年
岩石成因
构造环境
Nanshan, Qinghai province
northern margin of the West Qinling
Gouhou complex
LA-ICP-MS zircon U-Pb dating
petrogensis
tectonic setting
