西准噶尔谢米斯台地区双峰式火山岩的发现及其地质意义
Discovery of Bimodal Volcanics and Its Geological Significance in the Xiemisitai Region, Western Junggar, China

摘要： 西准噶尔谢米斯台地区是研究准噶尔洋盆构造演化的关键地区，新发现的双峰式火山岩为开展研究提供了直接的载体，对其物质组成特征、岩石地球化学特征和锆石UPb年代学等进行研究，判别成因机制和大地构造环境，对恢复造山带大地构造格局有着重要的意义。本次研究获得如下认识：该套双峰式火山岩为碱性玄武岩-钙碱性流纹岩组合，流纹岩LAICPMS锆石UPb年龄(4318±23) Ma；玄武岩来源于俯冲流体交代的地幔部分熔融，流纹岩来源于地壳物质的部分熔融；双峰式火山岩形成于早志留世弧后盆地初始演化阶段；结合前人的研究成果，认为西准噶尔谢米斯台地区在早古生代存在完整的沟-弧-盆体系。
Abstract: The Xiemisitai region in the Western Junggar is a key region to investigate the tectonic evolution of the Junggar ocean basin. The discovery of the Xiemisitai bimodal volcanics and their composition, petrogeochemistry, and zircon UPb age are important to discriminate formation mechanism and tectonic setting, reconstruct the tectonic framework of Western Junggar orogenic belt. The following acquaintances were obtained by this paper.The bimodal volcanics are composed of alkaline basalt and calcalkaline rhyolite, and the LAICPMS zircon UPb dating of the rhyolite is (4318±23) Ma. The mafic magma was likely derived from partial melting of the mantle metasomatized by subductionrelated fluid, and the felsic magma was derived from the partial melting of crust materials. The bimodal volcanics may have formed in an early Silurian incipient backarc basin. Combined with previous studies, we suggest that there was a complete Early Paleozoic trencharcbasin system in the Xiemisitai region, Western Junggar