羌塘沱沱河地区多才玛二长岩SHRIMP锆石U-Pb年代学及岩石地球化学

摘要

The Duocaima Pb-Zn deposit is located in the northeast margin of Qiangtang block of Qinghai.The authors undertook a detailed study of zircon U-Pb dating and geochemistry of the monzonite in Tuotuohe mining area.The results indicate that the monzonite is calc-alkaline to high-K calc-alkaline and aluminous,and is characterized by relatively high Na2O,low K2O and MgO.The samples have higher Rb/Sr (0.21 ～0.47),lower Nb/Ta (13.25 ～ 14.02),and low Mg#,etc.,indicating that the monzonite was derived from crust.The samples are enriched in LREE,LILE (e.g.,Rb,Ba,K,Sr),and active incompatible elements (e.g.,Th,U),and depleted in HFSE (e.g.,Nb,Ta,P,Ti),similar to the characteristics of volcanic arc magmas.The SHRIMP zircon U-Pb dating of the monzonite yields Late Cretaceous to Early Paleocene ages (65.8 ± 1.1Ma).Combined with regional geological background,it is concluded that the monzonite was probably formed during the late stage of deep subduction of Tethys Oceanic Plate.%对青海省羌塘地块东北缘沱沱河多才玛铅锌矿区二长岩进行了系统的锆石U-Pb年龄和地球化学研究.结果表明二长岩属于钙碱性-高钾钙碱性,准铝质岩石,具有较高的Na2O和较低的K2O、MgO.样品的高Rb/Sr比值(0.21 ～0.47)、低Nb/Ta比值(13.25～ 14.02)和低Mg#值等特征显示二长岩岩浆来源于地壳.样品富集轻稀土元素(LREE)、大离子亲石元素(LILE)(Rb,Ba,K,Sr),以及活泼的不相容元素(Th、U),同时亏损高场强元素(HFSE)(Nb、Ta、P、Ti),与弧火山岩特征相似.二长岩的SHRIMP锆石U-Pb定年结果为(65.8±1.1) Ma,显示其形成于晚白垩世—早古新世.结合区域地质背景,推测多才玛二长岩形成于特提斯大洋板块的后期深俯冲阶段.