新疆西准噶尔塔北地区晚古生代中酸性侵入岩的成因分析

Genesis of the granitoids intrusions in Tabei area,West Junggar,Northwest China: Evidences from geological and geochemical characteristics

塔尔巴哈台-萨吾尔地区位于西准噶尔北部，中酸性岩浆侵入作用十分强烈。本文对塔尔巴哈台．萨吾尔地区西段的塔北地区出露的克孜贝提、哲北、巴斯、卡姆斯台、阿西和科鲁克6个代表性中酸性岩体的地质、成岩年代和地球化学特征进行研究。结果表明，塔北地区中酸性岩浆作用可分为早石炭世早期（343-338Na）、早石炭世晚期（328-324Ma）和晚石炭世（315Ma）三个阶段：早石炭世早期中酸性岩体包括克孜贝提、哲北岩体；岩性主要为闪长岩，具有碱性、过铝质岩石的特点；早石炭世晚期中酸性岩体包括巴斯、卡姆斯台和阿西岩体，岩性主要为花岗闪长岩，具有钙碱性-碱性和准铝质．过铝质岩石的特点；晚古生代中酸性侵入岩体为科鲁克岩体，岩性为钾长花岗岩，具有碱性和过铝质岩石的特点。从早石炭世至晚石炭世，塔北地区中酸性岩具有向富K、si和贫Ca演化的趋势，研究源区以壳源为主、有幔源物质混入的特征；岩浆演化具有分离结晶增强、围岩混染减弱的特点。塔北地区早石炭世早期中酸性岩体形成于俯冲岛弧环境，旱石炭世晚期．晚石炭世岩浆侵位于后碰撞环境。

Taerbahatai-Sawuer district is located in the northwest part of the North Junggar area, where widely distribute granitoid intrusions. In this study, we focused on the six granitoid intrusions （named as Kezibeiti, Zhebei, Basi, Kamusitai, Axi and Keluke respectively） in Tabei area, west section of the Taerbahatai-Sawuer district. After detailed geological and petrological investigation, these six granitoid intrusions are dated by the zircon LA-ICPMS U-Pb method, and their diagenetic ages are between 343 - 315Ma, which can be subdivided into 3 stages： early stage （343 -338Ma） ; middle stage （328 - 324Ma） and late stage （315Ma）. In the early stage, the granitoid intrusions （Kezibeiti and Zhebei plutons） are diorite, with alkaline peraluminous characters. In the middle stage, the granitoid intrusions （Basi, Kamusitai, and Axi plutons） are granitic diorite, with calc-alkaline-alkaline and metaluminous- peraluminous character. In the late stage, the granitoid intrusion （Keluke pluton） is granite, with alkaline and peraluminous characters. From the early stage to late stage, the evolution trending of granitoid intrusions Tabei area are higher K, Si content and lower Ca content, their magmatic source are generally crust with some-degree mantle materials; and stronger fractional crystallization and less crustal assimilation. The petrogenetic discriminative indicators shows that the two early-stage plutons are formed within Arc subduction environment （343 - 338Ma）, while other four plutons are emplace with post-collisional environment （328 -315 Ma）.