甘肃阿克塞余石山铌钽矿区二长花岗岩成因和形成环境:来自年代学及地球化学的证据  

Petrogenesis and Forming Environment of Monzonitic Granite in Yushishan Nb-Ta Mining Area, Akesai, Gansu Province:Evidences from Chronology and Geochemistry

作　　者：廖风云 陈威[1] 曹晓峰[1,2] 陈广琛 何昆洋 杨文 吴义布[3] 李通国[3] Liao Fengyun;Chen Wei;Cao Xiaofeng;Chen Guangchen;He Kunyang;Yang Wen;Wu Yibu;Li Tongguo(School of Earth Resources,China University of Geosciences,Wuhan 430074,China;National Demonstration Center for Experimental Mineral Exploration Education,China University of Geosciences,Wuhan 430074,China;Gansu Geological Survey,Lanzhou 730000,China)

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]中国地质大学固体矿产勘查国家级实验教学示范中心,湖北武汉430074 [3]甘肃省地质调查院,甘肃兰州730000

出　　处：《地球科学》2020年第12期4589-4603,共15页Earth Science

基　　金：中祁连西段稀有金属矿产综合勘查示范项目(No.2017YFC0602404)。

摘　　要：余石山铌钽矿区位于北阿尔金-柴北缘-祁连的交汇部位,该区域构造演化复杂.为了揭示矿区内二长花岗岩的成因和形成环境,运用岩石学、岩石地球化学、锆石U-Pb年代学、锆石Lu-Hf同位素等理论及技术方法对该二长花岗岩进行了系统的研究.该二长花岗岩的详细定名为中细粒似斑状黑云二长花岗岩,暗色矿物以黑云母、角闪石为主.地球化学特征表明,余石山的二长花岗岩属于钾玄质准铝质-弱过铝质系列,富集Rb、Th、K等大离子亲石元素,相对亏损Nb、Sr、P、Ti等高场强元素,稀土元素配分曲线具有明显的负Eu异常,δEu的平均值为0.57,(La/Yb)N的平均值为11.09,说明该二长花岗岩体岩浆部分熔融程度较高.根据岩石学及地球化学特征可判断该岩体为I型花岗岩.锆石LA-ICP-MS U-Pb定年显示,该二长花岗岩的结晶年龄为481.3±1.7 Ma,形成于早奥陶世.锆石Lu-Hf同位素分析表明,锆石εHf(t)的值为+0.4^+11.8,均为正值,二阶段模式年龄的范围为675~1 308 Ma,指示其源岩主要为元古代新生地壳物质.该二长花岗岩的形成与早奥陶世时期北阿尔金洋壳俯冲中南祁连陆壳密切相关,在中南祁连陆壳边缘的余石山地区(弧后),由于洋壳俯冲导致了陆壳的伸展从而产生了裂隙,俯冲产生的熔融岩浆通过裂隙上侵而形成了该二长花岗岩岩体.The Yushishan Nb-Ta mining area is located at the junction of North Altun, Qaidam and Qilian, and the tectonic evolution of this area is complex. The research of petrology, rock geochemistry, zircon U-Pb chronology and zircon Lu-Hf isotope was carried out on the monzonitic granite to reveal petrogenesis and forming environment of it. The detailed name of the monzonitic granite is medium-fine-grained porphyritic biotite monzonitic granite and its dark minerals are mainly biotite and hornblende. The geochemical characteristics show that the monzonitic granite belongs to the typical high-K series with quasialuminous to weakly peraluminous. Large ion lithophile elements(Rb, Th and K) are relatively enriched and high field strength elements(Nb, Sr, P and Ti) are in distinct negative anomaly. The REE distribution patterns show negative Eu anomaly, with the mean δEu value of 0.57 and the mean(La/Yb)Nvalue of 11.09, they show that the monzonitic granite magma has a high degree of partial melting. The features of petrological and geochemical indicate that the monzonitic granite belongs to I-type granite. Zircon LA-ICP-MS U-Pb dating of the monzonitic granite yielded a crystallization age of 481.3±1.7 Ma and it was formed in the Early Ordovician. The zircons Lu-Hf isotope analysis shows that the εHf(t) ranges from +0.4 to +11.8 and the two-stage Hf model ages range from 675 to 1 308 Ma, suggesting that the source rocks are partial melting of Neoproterozoic juvenile crustal materials. The formation of the monzonitic granite was closely related to that North Altun oceanic crust subducted Middle-South Qilian continental crust, in the Yushishan area on the edge of Middle-South Qilian continental crust(back arc), the upward intrusion of molten magma from the fractures formed the monzonitic granite because of the subduction of the oceanic crust.

关 键 词：余石山 二长花岗岩 U-PB定年 地球化学 LU-HF同位素 岩石学 

分 类 号：P581[天文地球—岩石学]