北天山艾维尔沟东北部奇尔古斯套组硅质岩地球化学特征及地质意义

Geochemistry Characteristics and Geological Significances of Silicate from Qiergusitao Formation in Northeast Aiweiergou area,North Tianshan

为研究北天山艾维尔沟地区晚古生代沉积环境特征,以该地区上石炭统奇尔古斯套组中广泛分布的硅质岩为研究对象,开展岩石学、岩石地球化学特征等研究。该区硅质岩为非纯硅质岩,在Fe-Mn-Al三角图中样品位于生物成因区及附近,反映出较多外来物质的加入。Al/(Al+Fe+Mn)平均值0.59,δCe为1.28~1.98,显示为生物成因硅质岩。Al_(2)O_(3)/(Al_(2)O_(3)+Fe_(2)O_(3)),(La/Ce)_(N),(La/Yb)_(N)等特征比值及构造环境判别图,反映出硅质岩沉积环境为大陆边缘。结合陆源碎屑岩碎屑组分和副矿物特征,表明北天山洋残余洋盆规模有限,研究区大河沿组磨拉石沉积角度不整合于早期地层之上,标志残余洋盆最终闭合。

In order to study the sedimentary environment characteristics of the Late Paleozoic in Aiweiergou area of North Tianshan,the authors have conducted the petrological and geochemical analyses of the widely distributed silicate in Qiergusitao Formation of Upper Carboniferous.The siliceous rocks have similar phase behavior as nonhydrothermal siliceous rocks in the Fe-Mn-Al diagram,with a continuous supply of land-based materials during the deposition process.The average value of Al/(Al+Fe+Mn)is 0.60,δCe is 1.07~1.98,indicating that they are biogenic siliceous rocks.The ratios of Al_(2)O_(3)/(Al_(2)O_(3)+Fe_(2)O_(3)),(La/Ce)_(N) and(La/Yb)_(N) and tectonic environment discriminant diagram demonstrate that the silicate developed in a shallow-slope depesitional environment in the continental margin.Combining with composition of granule in sedimentary rock and para-mineral characteristics,it shows that the scale of the residual oceanic basin of North Tianshan ocean is limited.The angular inconsistency of the molassic-type deposition of the Daheyan Formation above the early stratum indicates the final closure of the residual ocean basin.