阿尔金南缘新元古代盖里克片麻岩年代学、地球化学特征及其构造意义

Zircon U-Pb Ages,Geochemical Characteristics and Tectonic Implications of Neoproterozoic Gailike Gneiss in the South Altyn Tagh

盖里克片麻岩分布于阿中地块亚干布阳—帕夏拉依档一带,岩体主要岩性由眼球状黑云斜长片麻岩、二云二长片麻岩组成。LA-ICP-MS锆石U-Pb定年得到206Pb/238U加权平均年龄值为（886.5±5）Ma,说明盖里克片麻岩原岩形成于新元古代早期青白口纪;地球化学结果显示：主量元素具有高SiO_2、Al_2O_3、K_2O＋Na_2O含量,低Na_2O、MgO、CaO和TiO_2含量的特征,A/CNK值介于1.03~1.17之间,属于高钾钙碱性系列的过铝质花岗岩。岩石富集Rb、Th、K等大离子亲石元素,亏损Nb、Ta、Sr、P、Hf、Ti等高场强元素,具有典型的大陆碰撞型花岗岩相应的元素丰度特征;岩石轻稀土富集而重稀土亏损,具有明显的负Eu异常,总体呈右倾的＂V＂型稀土分配模式,显示了典型的地壳重熔型花岗岩特征。盖里克片麻岩的源岩为地壳中角闪岩相基性岩类（变玄武岩）,形成于同碰撞构造环境。综上说明本区存在新元古代早期的构造岩浆事件,可能对应于新元古代的罗迪尼亚（Rodinia）超大陆汇聚事件,说明塔里木和柴达木板块之间在新元古代早期曾经存在板块的汇聚碰撞。

Gailike gneiss,located in the Yaganbuyang-Paxialayidang area at the Azhong Block,is composed mainly of augen biotite plagioclase gneiss and two-mica monzonitic gneiss. The U-Pb dating of zircons from the gneiss using LA-ICP-MS yields an age of（ 886. 5 ± 5） Ma,which indicates the protolith of Gailike gneiss was generated at Early Neoproterozoic era. The geochemical analysis shows that major element characterized by high SiO_2,Al_2O_3 and K_2O ＋ Na_2O contents,and low Na_2O,MgO,CaO and TiO_2 contents. A / CNK from 1. 03 to1. 17,which suggest that the protolith belongs to the typical high-K calc-alkaline series with peraluminous. The protolith is riched in large ion lithophile elements of Rb,Th,K and depleted in high field strength elements of Nb,Ta,Sr,P,Hf,Ti. These characteristics are similar to values of the continental collision type granite.REE distribution patterns show negative anomaly of Eu,distinct enrichments in LREE relative to HREE. The chondrite-normalized REE patterns are right-inclined,with a clear V trough. The protolith of the gneiss was mainly from the melting of basaltic rocks in crust and generated in the syn-collisional environment. These fea-tures indicate the existence of Early Neoproterozoic tectonomagmatic activity in Altyn Tagh area,and was related to the formation of the Rodinia supercontinent. It means that a collision and convergence between the Qaidam microplate and the Tarim Plate had taken place during the Neoproterozoic time.