西南天山东段基性火山岩地质及地球化学特征

Geological and Geochemical Characteristics of the Late Paleozoic Basic Volcanic Rocks in the Eastern Sector of the Southwestern Tianshan Mountains

西南天山东段色日克牙依拉克一带的基性火山岩主要为致密块状玄武岩、枕状玄武岩,与硅质岩、粉砂岩互层,沿走向火山岩不稳定,常相变为硅质岩、粉砂岩,其中枕状玄武岩枕状构造发育。玄武岩主量元素、稀土及微量元素特征与N-MORB玄武岩相似,综合判断该玄武岩应形成于N-MORB环境。根据放射虫鉴定、枕状玄武岩^(40)Ar/^(39)Ar同位素测年,结合前人在邻区的研究成果,确定火山岩形成年代应为早石炭世。据此可以确定南天山古洋在早石炭世仍存在并处于扩张阶段,晚古生代南天山洋盆最终闭合时限应在早石炭世之后。

The basic volcanic rocks in Serikeyayilake, eastern sector of the Southwest Tianshan Mountains are mainly composed of compact massive basalt and pillow basalt interbedded with the silicalite and siltstone. They are usually transformed into silicalite and siltstone along the strike. Pillow structure was developed in the pillow basalt. REE and trace elements geochemistry of the basalt is similar to that of N-MORB basalt. This shows that the basalt was formed in the N-MORB environment. Volcanic rocks should be formed in the Early Carboniferous on the basis of the radiolaria, 40Ar/39Ar dating for the pillow basalt and previous research in the adjacent regions. From this it is concluded that that old South Tianshan Ocean was in a spreading stage during the Early Carboniferous, and the final closing time of Late Paleozoic South Tianshan Ocean basin should be after the Early Carboniferous.