广西来宾蓬莱滩剖面中上二叠统硅质岩的地球化学特征及沉积背景

广西来宾地区中上二叠统广泛发育硅质岩,蓬莱滩剖面和铁桥剖面是本地区中上二叠统出露最好的剖面.本文对蓬莱滩剖面28件硅质岩(分别为中二叠统茅口组3件与上二叠统合山组25件)的主量和稀土元素进行了分析研究,并结合岩石学特征,认为:蓬莱滩剖面合山组硅质岩沉积于受到陆源物质影响的边缘海盆环境,它们的硅质主要来源于硅质生物,为生物成因;而其茅口组硅质岩则沉积于远离陆源物质影响的边缘海盆环境,它们的硅质主要来源于热液,为热液成因.通过与铁桥剖面的热液成因硅质岩的沉积背景对比研究,结果表明:中晚二叠世时期,来宾地区为富硅的边缘海盆环境,而陆源物质输入程度的差异是造成本地区形成不同成因硅质岩的主要因素.

Geochemistry and sedimentary background of the Middle-Upper Permian cherts in the Penglaitan section,Laibin,Guangxi Province

The Middle-Upper Permian cherts occur extensively in Laibin area, Guangxi Province, in which the Penglaitan section and the Tieqiao section well expose them. In this study, 28 bedded chert samples (3 samples from the Maokou Formation of the Middle Permian and 25 samples from the Heshan Formation of the Upper Permian) were analyzed for major and rare earth elements. Based on the results of major and rare earth element contents of these samples and lithofacies characteristics of them, we considered that bedded cherts from the Heshan Formation in the Penglaitan section deposited in marginal sea basin environment influenced by terrigenous materials and silica of them derived from siliceous organism as biogenic origin, whereas, those from the Maokou Formation deposited in marginal sea basin environment without influence of terrigenous materials and silica of them primarily derived from hydrothermal fluid as hydrothermal origin. Comparing sedimentary background of bedded cherts in the Penglaitan section with those as hydrothermal origin in the Tieqiao section, this study showed that Laibin area developed a marginal sea basin environment rich in silica during the Middle-Late Permian and discrepancy in influence of terrigenous materials controlled the different origin of bedded cherts in Laibin area.