新疆哈尔里克早石炭世A型花岗岩的岩石成因及构造意义

PETROGENESIS AND TECTONIC SIGNIFICANCE OF EARLY CARBONIFEROUS A-TYPE GRAINTE IN HARLIK,XINJIANG

对出露在哈尔里克山西段小白杨沟—南山口一带的早石炭世花岗岩进行了锆石LA-ICP-MS U-Pb定年,结果为331.3±1.9 Ma,属早石炭世晚期。其岩石组合为碱长花岗岩、碱性花岗岩,暗色矿物以黑云母为主,见钠质角闪石,具富碱、贫钙镁和低铝铁的特征,微量元素明显富集Rb、Th、K等大离子亲石元素和Zr、Hf等高场强元素而强烈亏损Ba、Sr、Eu等元素,10000 Ga/Al值变化于2.93~3.80之间,表明该碱性花岗岩属于典型的A型花岗岩,具板内花岗岩特征,并非前人认为的岛弧花岗岩,其正εNd(t)值(+5.66^+6.12)和年轻的Nd模式年龄(T_(DM2)=0.60~0.62 Ga)显示岩浆来源于新生年轻地壳。从本次1∶50000区调研究成果看,博格达自早石炭世开始伸展,早石炭世晚期进入闭合阶段,哈儿里克山早石炭世晚期岩体应处于博格达裂谷晚期阶段,并非前人所说的后碰撞和岛弧环境。

The alkali-feldspar granite is located at the area of Nanshankou,western part of the Harlik Mountain. Its LA-ICP-MS zircon U-Pb age is 331. 3 ± 1. 9 Ma. Therefore,the granite is formed in the late stage of Early Carboniferous. The dark minerals in the rock are mainly biotite,with litte Na amphibolite. This type of granite is riched in alkali elements,poor in calsium,magnesium,and has low content of aluminum and iron oxide. The rock is riched in large ion lithosphile elements,such as Rb,Th and K. It has abundant HFSE elements and depleted in Ba,Sr and Eu. The 10000 Ga / Al value is varied from 2. 93 ~ 3. 80. It indicates that the rock is A-type granite,formed in intraplate tectonic settings,instead of the previous island arc environment. ItsεNd（ t） values range from 5. 66 to 6. 12,the Nd model ages are 600 ~ 620 Ma. It tells that the magma may originate from the young crust. Based on the results of the 1∶ 50000 regional geological survey,the Bogada rift was extended during Early Carboniferous,and closed at the late stage of Early Carboniferous. The Late Early Carboniferous alkali-feldspar granites should formed in the rift environment,instead of coming from the previous post-collisional or arc tectonic setting.