西天山阿吾拉勒石炭纪火山岩年代学和地球化学研究

西天山阿吾拉勒裂谷带内广泛发育石炭纪火山岩, 主要由玄武岩、粗面玄武岩、玄武质粗安岩、玄武质安山岩、粗面岩和流纹岩组成。以中基性岩为主, 多为钙碱性系列。LA-ICP-MS锆石U-Pb测年结果显示, 区内流纹岩形成于(316.1±2.2) Ma, 为早石炭世晚期。微量和稀土元素特征表明, 本区的火山岩具有俯冲带大陆边缘岛弧火山岩的典型特征, 应形成于早石炭世晚期的准噶尔洋向伊犁板块俯冲的大陆边缘弧环境。可能是由受俯冲流(熔)体交代的地幔楔尖晶石二辉橄榄岩发生1%~5%的部分熔融, 并在上升过程中经历了不同程度的结晶分离和同化混染作用而形成的。

Zircon U-Pb Chronology and Geochemistry of Carboniferous Volcanic Rocks in Awulale Area, Western Tianshan Mountains

Carboniferous volcanic rocks are widespread in Awulale rift zone area. Geochemical data suggest that they belong to calc-alkalic series, and consist of basalt, trachybasalt, basaltic trachyandesite, basaltic andesite, trachyte and rhyolite. LA-ICP-MS zircon dating of the rocks yielded an isotopic age of (316.1±2.2) Ma, which represents the late Early Carboniferous. Their major and trace element geochemistry shows that these volcanic rocks are characterized by the enrichment of large ion lithophile elements, suggesting that they had a very intimate relationship with volcanic-arc rocks and probably resulted from the northward sudbuction of the Junggar Ocean beneath the Ili-Middle Tianshan Plate. They might have been formed from a partially melted (about 1%~5%) lithospheric mantle (probably spinel-lherzolite) source that had been enriched with subduction fluids, and experienced extensive fractional crystallization and crustal contamination before eruption.