东昆仑驼路沟钴(金)矿床千枚岩碎屑锆石年代学、Lu-Hf同位素特征及其地质意义

Detrital Zircon Geochronological and Lu-Hf Isotopic Characteristics of Phyllite from Tuolugou Cobalt (Gold) Deposit,East Kunlun and Their Geological Significance

青海驼路沟钴(金)矿床内发育一套浅变质海相火山-沉积岩系,该套火山-沉积岩系形成时代及构造属性存在争议。本文对该套地层中的绿泥绢云千枚岩样品进行了锆石LA-ICP-MS测年、Lu-Hf同位素和岩石地球化学研究,对其原岩沉积时代、沉积物源及基底构造亲缘性进行了探讨。年代学结果表明,该套浅变质海相火山-沉积岩系碎屑锆石最年轻的年龄组为433~412 Ma,加权平均年龄为(422.8±6.8)Ma,结合区域构造岩浆事件资料认为其原岩沉积时代上限为晚志留世。433~412 Ma年龄组的ε(t)值为-2.02~5.47,平均为1.80,表明该组锆石的母岩主要为新生的地壳物质;其一阶段年龄为1124~829 Ma,说明这些锆石的母岩浆来自Grenvillian期Rodinia超大陆汇聚时的壳幔相互作用。岩石地球化学结果显示,驼路沟千枚岩的原岩可能为一套泥砂质沉积岩,沉积环境为稳定的被动大陆边缘环境,其沉积环境与区域构造演化研究一致,即昆中洋于430 Ma左右俯冲结束,东昆仑地区开始进入板内伸展环境,而昆南地块南部地区于晚志留世进入被动大陆边缘环境。碎屑锆石U-Pb年龄谱综合分析表明,太古宙时期碎屑锆石源区属性并不明确,中—新元古代昆南地区的基底与华南克拉通具有明显亲缘性。自Grenvillian造山运动形成华夏—扬子—昆仑—柴达木—祁连联合大陆,至泛非期(650~550 Ma)昆仑陆块可能已从联合大陆中分离出来。

A set of epimetamorphic marine volcano-sedimentary rock series developed in Tuolugou cobalt(gold)mining area,Qinghai Province,of which the formation ages and tectonic attributes are controversial.In this paper,zircon LA-ICP-MS dating,Lu-Hf isotopic and geochemical analysis were carried out on the phyllites from Tuolugou deposit,and their protolith depositional ages,sediment provenance and tectonic affinity of the basement were discussed.The chronological results show that the youngest age group of detrital zircons is 433-412 Ma with weighted average age of(422.8±6.8)Ma.Combined with the data of regional tectonic magmatic events,the upper limit of the protolithic depositional age is the Late Silurian.Theε(t)values of zircons in age group of 433-412 Ma range from-2.02 to 5.47,with an average of 1.80,indicating that the parent rocks of this zircon group are mainly new crustal materials.The Tage ranges from 1124 to 829 Ma,indicating that the zircons originated from the crust mantle interaction during the convergence of the Rodinia supercontinent in the Grenvillian period.The petrogeochemical results show that the protolites of the Tuolugou phyllites may be a set of mud-sandy sedimentary rocks,and the depositional environment is a stable passive continental margin.It is consistent with the result of regional tectonic evolution which is:The subduction of the middle Kunlun Ocean ended around 430 Ma,and the whole east Kunlun area began to enter the intraplate extension setting,while the southern part of the south Kunlun block entered the passive continental margin in the Late Silurian.The comprehensive analysis of the U-Pb age spectrum of detrital zircons shows that the original properties of detrital zircons during the Archean is not clear,and the basement of the south Kunlun in the Mesoproterozoic has obvious affinity with the South China craton.Since the Grenvillian orogeny formed the United Continent of Cathaysia-Yangzi-Kunlun-Qaidam-Qilian,the Kunlun block may have been separated from the United Continent during the Pan-African period(about 650-550 Ma).