新疆吾拉斯台一带下二叠统乌郎组火山岩地球化学特征

GEOCHEMISTRY OF VOLCANIC ROCKS OF THE LOWER PERMIAN WULANG FORMATION IN WULASITAI AREA,XINJIANG

乌郎组火山岩分布于哈萨克斯坦-准噶尔板块(Ⅰ级)伊犁-伊塞克湖微板块(Ⅱ级)阿吾拉勒晚古生代裂谷系(Ⅲ级)中,为一套陆相的火山岩和碎屑岩组合.吾拉斯台一带火山活动较强,火山堆积厚度巨大,区内厚近4000 m,属乌郎组中上部层位.火山岩主要由偏碱性的基性和酸性岩组成,总体以双峰式火山岩为特征.岩石地球化学所反映的构造环境为板内玄武岩和大陆裂谷玄武岩,这与所处的大地构造位置相吻合.顶部层位的粗面玄武岩207Pb/206Pb同位素年龄为285±30 Ma,时代为早二叠世.由此推断,阿吾拉勒晚古生代裂谷系火山活动在早二叠世时即将结束,之后晚二叠世接受陆相磨拉石堆积,进入稳定陆内盆地发展阶段.

The volcanic rock of Lower Permian Wulang formation, distributed in the Late Paleozoic Awulale rift of IliYisaikehu micro-plate, Kazakhstan-Junggar plate, is the assemblage of continental volcanic rocks and detrital rocks. Intense volcanic activities in the area left thick volcanic accumulation up to 4000m, which belongs to the middle and upper layers of Wulang formation. The volcanic rocks are dominated by alkali-basic rocks and acidic rocks, characterized by bimodal. Lithogeochemistry shows a tectonic environment of intraplate basalt and continental rift basalt, which is in accordance with its tectonic location. The trachybasalt in the top layer is dated as Early Permian, with 207pb/206pb isotopic age of the 285±30 Ma. It is suggested that the volcanic activities of the Late Paleozoic Awulale rift tended to end in Early Permian. Then continental molasse was cumulated in Late Permian, marking the start of stable developing period of intracontinental basin.