西藏纳如松多矿区晚白垩世石英闪长岩锆石原位Hf-O同位素特征与岩石成因

拉萨地体的增生演化受到新特提斯洋俯冲的制约, 新特提斯洋于中生代启动北向俯冲, 在拉萨地体南部形成晚白垩世"岩浆大爆发"。纳如松多铅锌矿床位于中拉萨地体南缘, 矿区内晚白垩世石英闪长岩的岩浆源区特征及成因机制目前尚未得到很好的解释。通过矿区内该石英闪长岩的SHRIMP锆石U-Pb年龄与Hf-O同位素组成研究, 结果表明, 纳如松多石英闪长岩结晶年龄为83.0±1.0 Ma, 锆石εHf(t)和二阶段模式年龄TDM2分别为-2.6~1.0(平均值为-0.8)和1139~1363 Ma(平均值为1253 Ma); δ18O值介于6.5‰~7.9‰之间(平均值为7.2‰)。锆石原位Hf-O同位素组成指示, 石英闪长岩源区具有壳幔二端元混合的特征, 二端元混合模式计算显示幔源岩浆贡献较大, 且存在成熟地壳物质加入。纳如松多石英闪长岩与南拉萨地体晚白垩世岩浆的活动时间和动力学背景一致, 是拉萨地体南部晚白垩世岩浆大爆发事件的一部分, 指示由新特提斯洋北向俯冲引起的晚白垩世强烈岩浆活动的范围不局限于南拉萨地体, 还延伸到中拉萨地体。

In situ zircon Hf-O isotopic characteristics and petrogenesis of Late Cretaceous quartz diorite in the Narusongduo Pb-Zn mining area,Tibet

The accretion and evolution of the Lhasa Terrane is restricted by the subduction of the Neo-Tethys Ocean.The northward subduction of the Neo-Tethys Ocean started in the Mesozoic and formed the Late Cretaceous "magmatic burst" event in the south Lhasa Terrane.The Narusongduo Pb-Zn deposit is located in the southern margin of the central Lhasa Terrane.The nature of the magma source and petrogenesis of the quartz diorite in the mining district have not been well documented.The zircon SHRIMP U-Pb age and Hf-O isotopic characteristics of the quartz diorite are systematically reported in this study.The quartz diorite has SHRIMP U-Pb ages of 83.0 ±1.0 Ma, εHf(t)values of -2.6 to 1.0(mean = -0.8)and the corresponding TDM2 of 1088 Ma to 1312 Ma(mean=1253 Ma), and δ18O values between 6.5‰ and 7.9 ‰(average value = 7.2‰), indicative of an enriched source.In situ zircon Hf-O isotopic compositions display a binary mixing trend between mantle and continental crust, with the mixing calculations show in the mantle as a primary contributor.The Narusongduo quartz diorite has similar ages and geodynamic setting as the Late Cretaceous "magmatic burst" event in the southern part of Lhasa Terrane, implying that the Late Cretaceous magmatic activities triggered by the northward subduction of the Neo-Tethys Ocean were not limited in the south Lhasa Terrane and also extended to the central Lhasa Terrane.