青海夏日哈木矿区中泥盆世闪长玢岩锆石U-Pb年代学、地球化学及其地质意义

夏日哈木矿区的闪长玢岩主要出露于矿区北部。闪长玢岩LA-MC-ICP-MS锆石U-Pb年龄为（381.7±1.9） Ma，MSWD=0.20，属中泥盆世；结合闪长玢岩侵入成矿杂岩体的野外产状，研究表明夏日哈木镍矿的形成早于381.7±1.9 Ma。岩石学及化学成分显示其属于钙碱性、偏铝质系列闪长玢岩。岩体富Na（K2O/Na2O值为0.45~0.60），稀土元素总量较低（ΣREE为128.28×10-6 ~ 141.65×10-6），轻重稀土分馏明显，（La/Yb）N值为6.86 ~ 7.96；根据其较高的La/Nb值（3.32~3.76，平均3.57）、Th/Nb值（0.95～1.02，平均为0.99）以及Th/La值（0.266～0.291，平均0.278），结合源区判别图解，研究表明该岩石为下地壳部分熔融的产物。综合区域地质演化背景，表明夏日哈木矿区闪长玢岩形成于造山后伸展向板内过渡的环境。

Geochemistry,Zircon U-Pb Dating and Geological Significance of Diorite Porphyrite in Xiarihamu Deposit,Eastern Kunlun Orogenic Belt,Qinghai

Diorite porphyrite mainly emerges in the north part of Xiarihamu Cu-Ni deposit in Qinghai province. The zircon LA-MC-ICP-MS U-Pb dating result of diorite porphyrite is 381.7±1.9 Ma (MSWD = 0.20), which falls into Middle Devonian. Considering field occurrence of diorite porphyrites intruding mineralization complex, it is demonstrated that the Xiarihamu Ni deposit formed before Middle Devonian. The petrology and chemical components of diorite porphyrite show that they are calc-alkaline and metaluminous rocks with the characteristics of high-Na (K2O/Na2O = 0.45-0.60), low ΣREE (128.28×10-6-141.65×10-6) and obvious fractionation of LREE and HREE ((La/Yb)N = 6.86-7.96). It has relatively high ratio of La/Nb (3.32-3.76, and the average is 3.57), Th/Nb (0.95-1.02, and the average is 0.99) and Th/La (0.266-0.291, and the average is 0.278). It can be concluded that the diorite porphyrite is the product of lower crustal partly melting according to discrimination diagrams. Combining with the regional tectonic evolution background, the diorite porphyrite in Xiarihamu Cu-Ni deposit is formed in the extension to intraplate tectonic setting.