内蒙古赵井沟钾长花岗岩锆石U-Pb定年、Hf同位素和岩石地球化学特征

Zircon U-Pb dating and Hf isotopic and geochemical characteristics for K-feldspar granite in Zhaojinggou,Inner Mongolia

赵井沟铌钽矿与区内花岗岩关系非常密切,锆石LA-ICP-MS U-Pb定年结果表明矿区内黑云母钾长花岗岩形成时代为125±1 Ma。岩石地球化学分析结果显示,矿区内晚中生代岩浆岩为准铝质-弱过铝质碱性岩类,属于高钾钙碱性系列,具有轻稀土元素富集、Eu强负异常、大离子亲石元素(Rb、Th、U)和高场强元素(Hf、Y)强烈富集的地球化学特征,属于A1亚类的A型花岗岩;锆石^(176)Hf/^(177)Hf值介于0. 000 5～0. 003 0之间,ε_(Hf)(t)值为-15. 42～-5. 55,对应的模式年龄t_(DM2)变化于2 247～1 640 Ma之间。花岗岩浆主要来源于地壳物质部分熔融的产物。

The Zhaojinggou Nb-Ta deposit has close relationship with granite. Zircon LA-ICP-MS U-Pb dating indicates that the age of biotite K-feldspar granite in the mining area is 125 ± 1 Ma. Geochemical data show that the Late Palaeozoic magmatic rock is characterized by metaluminous alkaline rock, high potassium and alkali,enrichment of LREE with strong negative Eu anomaly and enrichment of LILE( Rb,Th and U),and strong negative anomalies of Hf and Y in primitive mantle-normalized spidergrams. It thus belongs to A1 subtype of A type granites,and has176 Hf/177 Hf ratios in the range of 0. 000 5 ~ 0. 003 0,ε Hf( t) values in the range of-15. 42 ^-5. 55 and corresponding model ages( tDM2) between 2 247 and 1 640 Ma. Granite was formed in a post-orogenic setting,mainly derived from the partial melting of crustal materials.