东昆仑夏日哈木矿区新元古代早期二长花岗岩锆石U-Pb年代学、地球化学及其构造意义

摘要

本文报道了东昆仑造山带中部夏日哈木矿区二长花岗岩体的锆石U-Pb年代学和全岩地球化学资料,以确定岩体的形成时代、岩石成因及其构造属性.夏日哈木矿区的二长花岗岩呈岩株状和脉状捕虏体出露于矿区中部.2件二长花岗岩样品中岩浆锆石LA-MC-ICP-MS U-Pb加权平均年龄分别为923.7±2.5 Ma (MSWD=0.27)和920.1±2.8 Ma (MSWD=0.18),属新元古代早期.岩石高硅(SiO2=73.24％～73.83％)、富碱(Na2O+K2O=7.96％～9.79％)、贫钙(CaO=0.31％～1.13％)、贫镁(MgO=0.11％～0.21％),属于高钾钙碱性、过铝质系列花岗岩;稀土配分曲线呈现轻稀土元素相对富集的右倾分布特征,具明显的Eu负异常(δEu=0.30～0.45);原始地幔标准化微量元素蛛网图显示Sr、Ba、Nb、P、Eu和Ti的负异常.岩石学及地球化学特征表明其属于S型花岗岩.岩石具有较低的CaO/Na2O比值(介于0.13 ～0.26之间,平均0.19),较高的Rb/Sr比值(介于1.27～12.45之间,平均7.61),显示出上部地壳源区的成分特征,可能由泥质岩石部分熔融形成.结合区域构造演化及构造判别,本文认为该区二长花岗岩形成于同碰撞的构造环境,岩石成因可能与加厚陆壳上部泥质岩石减压熔融并经历了斜长石等矿物的分离结晶作用有关,热源主要来自于陆壳加厚过程中K、Th、U等元素放射性蜕变产生的热量.综合分析认为,东昆中隆起带中部地区存在新元古代早期的岩浆活动,时间上对应于全球Rodinia超大陆的汇聚时间.%In this paper,we present zircon U-Pb dating,major and trace element geochemical data for the monzogranite intrusion in the Xiarihamu ore district which is located in the middle part of the East Kunlun Mountain Belt.Our aim is to elucidate the formation time,petrogenesis and tectonic setting of the intrusion.U-Pb dating of zircons from two monzogranite samples yielded weighted mean 206pb/238U ages of 923.7±2.5 Ma (MSWD=0.27) and 920.1±2.8 Ma (MSWD=0.18),respectively.The monzogranite is peraluminous and belongs to the high-K calc-alkaline series.The monzogranite is characterized by high SiO2 (73.24％-73.83％),high alkali (Na2O+K2O=7.96％-9.79％),low CaO (0.31％-1.13％) and MgO (0.11％-0.21％) contents.The monzogranite is enriched in LREE and relatively depleted in HREE with significant negative Eu anomalies (δEu=0.30-0.45),showing significant Sr,Ba,Nb,P,and Ti depletion on primitive mantle-normalized trace elements diagrams.Petrological and geochemical evidence indicates that the monzogranite belongs to S-type granite.The low CaO/Na2O ratios (ranging from 0.13 to 0.26,and the average value is 0.19) and high Rb/Sr ratios (ranging from 1.27 to 12.45,and the average value is 22.63) of the rock indicate a upper crustal origin,maybe associated with the partial melting of argillaceous rocks.Combined with regional tectonic evolution and discrimination of tectonic setting,we suggest that the monzogranite was formed in a syn-collision compression setting.The genesis of monzogranite maybe relevant with decompression partial melting of argillaceous rocks located in the thicken upper crust and the subsequent fractional crystallization of feldspar,etc.The main heat source may be provided by the in situ decay of K,U and Th.In summary,there exists an Early Neoproterozoic magmatic activity in the central part of Eastern Kunlun middle uplifted basement and granitic belt,which responded to the amalgamation of the Rodinia supercontinent.