新疆西准噶尔北部谢米斯台-赛尔山地区早-中古生代火山岩及其构造意义

The West Junggar in Xinjiang is characterized by widespread development of Late Carboniferous to Permian post-collisional granitoids and volcanic rocks， but little is known about the Devonian and older magmatism in the West Junggar, leading to an incomplete recognition of its Paleozoic tectonic history. We have reported that there are some Middle Paleozoic A-type granites and associated mafic to felsic plutons across the Xiemisitai-Saier Mountains in northern West Junggar, but this preliminary work was restricted within the geochronological study. In this project, on the base of detailed investigations in the field, the representative volcanic and subvolcanic rocks throughout the Xiemisitai-Saier Mountains would be dated by zircon U-Pb dating method to establish the whole geochronological framework of magmatism in this region. Petrological, geochemical and isotopic analysis on these rcoks would be performed to reveal their petrogenesis and source features. All the data from this project and those avalible in the adjacent region would provide key insights into the Early to Middle Paleozoic acceretionary orogen process in northern West Junggar and help to understand the whole Paleozoic tectonic evolution of this region.

新疆西准噶尔地区以大量发育晚石炭世-二叠纪后碰撞型花岗质岩体和火山岩为特征，但由于很少有关泥盆纪和更早岩浆活动的报道，从而导致对该区整个古生代的演化认识并不完整。虽然项目申请者曾经报道了在西准噶尔北部的谢米斯台-赛尔山地区存在少量晚志留世-早泥盆世A型花岗岩及伴生的基性-酸性岩体，但仅限于年代学研究。本项目拟在系统的野外调查基础上，侧重立足于对谢米斯台-赛尔山地区广泛分布的火山岩、次火山岩进行锆石U-Pb测年来建立该区岩浆作用完整的年代学框架，准确限定早-中古生代岩浆作用的时限；对火山岩的岩石学、矿物学、元素地球化学、Sr-Nd同位素的系统分析来识别早-中古生代岩浆的成因、演化特征及源区性质。结合本区早-中古生代岩浆特征及邻区地质资料，加深对西准噶尔北部早-中古生代增生造山过程的理解，确立西准噶尔北部古生代完整的构造演化模型。

西准噶尔北部以东西走向构造单元区别于西准噶尔中、南部地区，其最近发现的中古生代岩浆活动对更全面认识其构造演化具有重要意义。本项目选取西准噶尔北部谢米斯台-赛尔山广泛分布的火山岩、次火山岩及代表性侵入岩体作为研究对象，经过详细的野外调查与系统的室内测试分析，获得若干重要数据资料，取得的主要成果包括:（1）谢米斯台-赛尔山地区存在晚奥陶世-早志留世（446~437Ma）火山活动，并发育同期的侵入岩（~440Ma），但并未发现前寒武基底。早古生代岩浆活动的确立进一步证明该区属于博什库尔-成吉斯岛弧的东段。研究区内以早泥盆世（420-410Ma）火山岩-侵入岩广泛分布为特征。（2）谢米斯台-赛尔山晚奥陶世-早志留世火山岩-侵入岩表现出钙碱性、岛弧岩浆的地球化学特征，具有亏损地幔为主的同位素特征，可能形成于准噶尔洋早古生代的由南向北的俯冲环境。（3）谢米斯台-赛尔山早泥盆世中-基性火山-侵入岩表现出富水的岩石学特征，酸性岩浆以A型花岗质岩浆为主，均中度-强烈富碱，具有亏损地幔为主的同位素特征。综合区域地质资料，认为其形成于西准噶尔晚志留世首次拼贴聚合后的后碰撞伸展环境。（4）中古生代同样是西准噶尔发生地壳生长的重要阶段。.相关成果已发表在《Journal of Asian Earth Sciences》上，也为后续研究奠定了坚实的基础。