南祁连化隆地区鲁满山花岗岩的岩石成因:地球化学、锆石U-Pb年代学及Hf同位素约束  

Petrogenisis of Lumanshan granites in Hualong area of southern Qilian Mountain:Constraints from geochemistry,zircon U-Pb geochronology and Hf isotope

作　　者：郭周平[1] 李文渊[1] 张照伟[1] 高永宝[1] 张江伟[1] 李侃[1] 孔会磊[1] 钱兵[1] 

机构地区：[1]中国地质调查局西安地质调查中心国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《中国地质》2015年第4期864-880,共17页Geology in China

基　　金：中国地质调查局地质调查项目"青海省化隆县甘都地区铜镍矿调查评价"(1212010918024);"青海省门源县银灿-浪力克1:5万成矿预测"(1212011221043)及"青海门源县宁缠河-牛头山一带铜多金属矿调查评价"(12120115022401)联合资助

摘　　要：位于南祁连化隆地区的鲁满山花岗岩体，岩石类型主体为黑云二长花岗岩。LA—ICP—MS锆石u—Pb定年测得其成岩年龄为（452．9-4-1．8）Ma，属于加里东期岩浆活动的产物。化学组成上，岩体具有高硅、富碱的特征，属于弱过铝质高钾钙碱性系列。微量和稀土元素组成上，岩体富集大离子亲石元素Rb、U、Th、K和Pb，亏损Ba、Sr、Ta、Nb、P、Ti，具明显轻稀土富集，重稀土亏损特征，显示较强烈的负Eu异常（6Eu=0．06～0．55，平均0．31），综合地质地球化学资料指示该岩体应属于高分异的I型花岗岩。锆石Hf同位素分析结果显示，岩体的eHf（t）为-7．4～0．1，二阶段模式年龄介于1425～1930Ma，指示成岩过程中应有亏损地幔组分参与，其壳源源区很可能包括化隆岩群。结合区域构造演化，认为鲁满山花岗岩体形成于柴北缘洋壳与中南祁连陆壳俯冲碰撞的地球动力学背景下，由幔源岩浆与其诱发的地壳物质熔融产生的长英质岩浆在地壳深部混合后再经历分异演化形成。The pluton in Lumanshan of Hualong area, located in southern Qilian Mountain, is mainly composed of biotitic monzogranites. Zircon LA-ICP-MS dating yielded a concordant age of 452.9~ 1.8 Ma, indicating that the pluton was formed in Caledonian. Geochemical data show that the Lumanshan pluton is silica enriched in alkali. It is a weakly peraluminous granite and belongs to the high-K calc-alkaline series. In trace and REE aspects, the granites are enriched in Rb, Th, U, K, Pb and LREE and depleted in Ba, Sr, Ti, P with strong negative anomaly of Eu （8Eu=0.06-0.55 with a mean value of 0.31）. Integrated geological and geochemical data suggest that the Lumanshan pluton should be genetically ascribed to highly fractionated I-type granites. The Hf isotope shows that the eHf（t） values of the pluton range from -7.4 to 0.1, with bM2 ages between 1425Ma and 1930Ma, indicating that depleted mantle materials had been involved in magma formation and the source region of granite probably included the Hualong Group. In combination with comprehensive analysis of the tectonic evolution, the authors hold that the Lumanshan pluton was formed in a subducfion-collision environment between the Qaidam and South Qilian terrane and most likely generated by mixing of a depleted mantle-derived magma and an induced crustal-melted felsic magma in the deep crust; later, it suffered further differentiation during magma ascent.

关 键 词：锆石U-PB年龄 地球化学 HF同位素 鲁满山花岗岩 南祁连化隆地区 

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