柴达木盆地西部昆北断阶带基底花岗岩锆石U-Pb年龄、地球化学特征及其地质意义

Zircon LA-ICPMS U-Pb dating and geochemistry of basement granites from north Kunlun faults zone,western Qaidam Basin and their geological implications

柴达木盆地西部基底分布有大量的有花岗岩类岩石。通过对柴达木盆地西部昆北断阶带钻遇的基底花岗岩样品开展详细的岩石学、锆石激光探针等离子体质谱u．Pb同位素年代学及岩石地球化学研究表明，锆石u—Pb同位素年龄为467—450Ma，显示基底花岗岩的结晶年龄为中-晚奥陶世，属于加里东期岩浆侵入旋回。详细的岩石地球化学分析表明，昆北断阶带基底花岗岩属过铝高钾钙碱性系列，其稀土元素配分模式为具有Eu负异常的轻稀土元素富集型，昆北断阶带中南部基底花岗岩属上地壳物质熔融，同碰撞环境下形成的花岗岩。综合区域上的研究成果，昆北断阶带及其以西地区存在中奥陶世-早志留世的加里东期构造．岩浆事件，这对探讨柴达木盆地西部基底花岗岩成因类型及岩浆演化具有重要的意义。

Lots of granitoids occur in north Kunlun faults zone of western Qaidam Basin. Comprehensive petrology, laser ablation ICPMS zircon U-Pb geochronology （LA-ICPMS U-Pb） and geochemistry of drilling basement granites were carried out from north Kunlun faults zone, western Qaidam Basin. Zircon U-Pb isotopic ages of 467 - 450Ma, i.e. Middle-Late Ordovician, show the crystallization age of the basement granites which belong to the Caledonian magmatic cycles. Detailed geochemical analyses show that the basement granites are per-aluminous and high-K calc-alkaline series, characterized by obvious LREE enrichment with medium to strong negative Eu anomalies. These geochemical features indicate that the basement granites probably resulted from crustal remelting of syn-collision setting. There exist Middle Ordovician-Early Silurian Caledonian tectonic-magmatic events, which provide important information for the researches on magmatic and tectonic evolution in north KunXun faults zone and its west.