兴蒙造山带南部图古日格地区徐尼乌苏组沉积相、物源分析及其构造意义

研究内蒙古西部图古日格地区徐尼乌苏组复理石建造的沉积相, 揭示其普遍具有不同厚度、不同类型的鲍玛序列, 属于浊流沉积相。参照浊积相模式, 将其归为中扇亚相, 包括辫状水道、辫状水道间和中扇前缘等3种微相。根据区域地层对比和最年轻锆石年龄峰值(437.9±2.7 Ma), 推测徐尼乌苏组的形成时代为早中志留世。物源分析发现, 徐尼乌苏组碎屑物质主要来自变质岩区的石英岩和火成岩区, 推测分别来自其北边的早古生代岛弧带和其南边的华北板块基底。图古日格、达茂旗和白乃庙3个地区的地层建造对比表明, 在南造山带东西方向约400 km范围内, 广泛发育以徐尼乌苏组和塔林宫群为代表的弧后盆地, 表明早古生代古亚洲洋的俯冲曾形成宽阔的沟弧盆体系, 因此推测华北板块北缘属于安第斯型活动大陆边缘。

Sedimentary Facies and Provenance Area Analysis of Xuniwusu Formation in Tugurige Area,Southern Xing-Meng Orogenic Belt and Their Tectonic Significance

Sedimentary facies studies on flysch formation of Xuniwusu Formation in Tugurige area, western Inner Mongolia reveal that the formation generally shows Bouma sequences with different thickness and types, in line with turbidity current sedimentary facies. According to turbidite facies model, it can be categorized into middle fan subfacies and contains three micro facies such as braided channel, inter-braided channel and central fan front margin microfacies. Xuniwusu Formation is speculated as the early-middle Silurian according to the regional stratigraphic correlation and the youngest peak of detrital zircon ages (437.9±2.7 Ma). Provenance analysis of Xuniwusu Formation reveals that it cames from the early Paleozoic island arc belt in the north and the basement of North China plate in the south, respectively. In addition, the strata comparison of Tugurige, Damaoqi and Bainaimiao areas suggests that a Back-arc Basin, representative of prevailing Xuniwusu Formation and Talingong Group, located in the south orogenic belt and extended about 400 km in East-West direction. Such a wide trencharc-basin system in early Paleozoic might be formed in relation to Paleo-Asia Ocean subduction and thus determines an Andean type active continental margin along the north edge of North China plate.