吐—哈盆地及周缘早二叠世火山岩地球化学特征及大地构造环境探讨

GEOCHEMISTRY OF EARLY PERMIAN VOLCANIC ROCKS AND THEIR TECTONIC SETTINGS FROM THE TURPAN-HAMI BASIN, XINJIANG

长期以来对吐—哈盆地及其周缘地区早二叠世构造环境的归属存在较大异议.通过对盆地早二叠世火山岩地球化学特征的研究,进一步厘定了火山岩的产出环境.研究表明,区内火山岩以玄武岩、玄武安山岩和流纹岩为主,具双峰式火山岩特征,大部分玄武岩相对MORB强烈富集LILE和LREE,HFSE适度富集,Th/Ta比值>5,Ta、Nb的适度亏损和陆壳的混染有关,少量玄武岩带有与消减作用有关的地球化学信息,与造山期后伸展环境下的火山岩地球化学特征相似.结合区域地质特征及邻区研究结果,认为吐—哈盆地早二叠世火山岩为造山期后伸展背景下裂谷环境的产物.

The Turpan-Hami basin in the east of Xinjiang is one of the most important petroliferous basins in China. It contains early Permian volcanic rocks including basalt, basaltic andesite and rhyolite. Geochemical analyses show characteristics of bimodal volcanic rocks. Discrimination diagram of REE and trace elements indicate that the volcanic rocks are of with-in-plate tholeiite affinity. In comparison with MORB, most basalts are highly enriched in LILE and LREE, and moderately in HFSE. The ratio of Th/Ta exceeds 5. The depletion of Ta and Nb may be interpreted as continental contamination, which similar to the geochemical characteristics of basalt in extensional settings in post-orogenic. Combining regional geological characteristics and its neighboring areas, we concluded that the Turpan-Hami basin in early Permian was in rift of extensional settings in post-orogenic.