青海南山地区加里东期强过铝质花岗岩锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb age, geochemical characteristics and geological significance of the Caledonian strongly peraluminous granites in the Nanshan area, Qinghai Province

作　　者：张永明[1,2] 裴先治 李佐臣 李瑞保 刘成军 裴磊 陈有炘 王盟 ZHANG Yongming;PEI Xianzhi;LI Zuochen;LI Ruibao;LIU Chengjun;PEI Lei;CHEN Youxin;WANG Meng(Faculty of Resources and Environmental Engineering,Shandong University of Technology,Zibo 255049,Shandong,China;Faculty of Earth Science and Resources,Chang’an University/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,MNR,Xi’an 710054,Shaanxi,China)

机构地区：[1]山东理工大学资源与环境工程学院,山东淄博255049 [2]长安大学地球科学与资源学院/西部矿产资源与地质工程教育部重点实验室/自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《地质通报》2019年第5期742-756,共15页Geological Bulletin of China

基　　金：国家自然科学基金项目《扬子地块西北缘碧口群构造属性及与Rodinia超大陆聚合-裂解关系》(批准号:41872233)、《秦岭-祁连结合部位早古生代晚期岩浆事件及其对构造演化的启示》(批准号:41872235)、《东昆仑东段晚古生代—早中生代构造演化与造山过程研究》(批准号:41472191);国家自然科学基金青年项目《东昆仑东段东昆中蛇绿岩年代学及构造属性研究》(批准号:41502191);中国地质调查局项目《青海省共和县曲什那地区1:5万三幅区域地质矿产调查》(编号:12120114041201)

摘　　要：青海南山地区位于南祁连构造带和西秦岭造山带的交接部位,在该地区元古宇变质地层中新厘定出一套含石榴子石白云母二长花岗岩,并对其进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb定年研究。结果表明,浪日娘含石榴子石白云母二长花岗岩结晶年龄为438.7±4.2Ma,形成于早志留世早期。岩石含石榴子石、白云母、电气石等高铝矿物,同时具高SiO2、富Al2O3特征,高铝饱和指数A/CNK=1.09~1.28,属高钾钙碱性强过铝质S型花岗岩;微量元素富集大离子亲石元素Cs、Rb、U、K和Pb,亏损高场强元素Nb、Ti、Zr、P和Ba、Sr;稀土元素总量低,配分曲线为轻稀土元素富集的右倾模式,具有弱-中等负Eu异常。高Rb/Sr值(1.83~3.95)、低CaO/Na2O值(0.11~0.19),伴随有Pb正异常和Ba负异常,暗示源区物质成分为泥质岩并经历了缺水熔融条件下的白云母脱水熔融。结合岩体年龄及区域地质资料,推断其可能形成于原特提斯洋闭合碰撞造山过程。The Nanshan area of Qinghai is located in the junction of the South Qilian belt and the West Qinling orogenic belt. A garnet- bearing muscovite monzogranite intruding into the Proterozoic metamorphic strata was newly recognized in Langriniang, Nanshan area of Qinghai. This paper reports the LA-ICP-MS zircon U-Pb dating result as well as petrology and geochemistry of this monzogranite. The crystallization age of the Langriniang garnet- bearing muscovite monzogranite was dated at 438.7 ± 4.2Ma.The Langriniang garnet- bearing muscovite monzogranites are characterized by high SiO2, Al2O3 and ASI (A/CNK=1.09~1.28) values. In addition, they have aluminous mineral assemblages of muscovite, tourmaline and garnet, showing typical features of strongly peraluminous S-type granites. Geochemically, the garnet-bearing muscovite monzogranites display enrichment of LREE and LILEs (e.g., Cs, Rb, K, U and Pb) and depletion of HREE and Nb, Ta, P, Zr, Ti, Ba and Sr, with weak to moderate negative Eu anomaly. Besides, the Langriniang monzogranites have high Rb/Sr ratios (1.83~3.95) and low CaO/Na2O ratios (0.11~0.19). These features indicate that the Langriniang monzogranites were derived from muscovite dehydration melting of metapelites under the water-absent condition. Combined with regional geology and age of the Langriniang monzogranites, the authors hold that the Langriniang monzogranites were formed during the closure of the Tethys Ocean and collision orogeny.

关 键 词：过铝质 S型花岗岩 加里东期 青海南山 LA-ICP-MS锆石U-P测年 

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