四川盆地西缘上二叠统宣威组顶部泥岩、砂岩的地球化学特征及其地质意义

沉积物源分析是认识盆山演化的重要途径。了解四川盆地西南缘上二叠统宣威组物源，对于重建晚二叠世扬子克拉通周缘演化具有重要意义。本文对峨眉山地区宣威组顶部泥岩、砂岩开展了岩石学和全岩地球化学分析，进行了物源、沉积环境和构造背景的研究。宣威组泥岩主要成分为黏土矿物，SiO₂含量(平均49.42%)中等；砂岩成分大部分为火山岩屑，含有少量石英及长石，具中等的SiO₂含量(平均44.12%),属于杂砂岩系列。泥岩与砂岩均具有轻稀土元素富集、重稀土元素较右倾的稀土元素配分型式，微量元素相对大陆上地壳富集高场强元素(如Nb、Zr),亏损大离子亲石元素(如Sr、Ba)。根据地球化学分析结果结合已发表的扬子克拉通周缘二叠系沉积岩数据，认为上二叠统宣威组顶部沉积岩物源区经历了强烈的化学风化作用，沉积古环境为富氧的淡水沉积环境；宣威组顶部沉积物物源不仅来自于近源搬运的峨眉山高Ti玄武岩，还接受了扬子克拉通的补给，扬子克拉通西缘晚二叠世时期是活动大陆边缘沉积。

Geochemical characteristics and geological implications of mudstones and sandstones at the top of the Upper Permian Xuanwei Formation on the western margin of Sichuan Basin

Provenance analysis is an important way to understand basin mountain evolution. Understanding the provenance of the Upper Permian Xuanwei Formation in the southwest margin of Sichuan Basin is of great significance for reconstructing the evolution of the Late Permian Yangtze Craton perimeter. In this paper, the petrology and whole-rock geochemical analyses of mudstone and sandstone at the top of Xuanwei Formation in the Emeishan area are analyzed, and the provenance, sediment environment and tectonic setting are studied. The mudstone of the Xuanwei Formation is mainly composed of clay minerals with medium SiO₂ content (average 49.42%); the sandstone is mostly composed of volcanic rock fragments, containing a small amounts of quartz and feldspar, with medium SiO₂ content (average 40.12%), belonging to the greywacke series. Mudstone and sandstone of Xuanwei Formation have light rare earth element enrichment, heavier rare earth elements are more right-leaning. Compared with the continental upper crust, trace elements are relatively rich in high field strength elements (such as Nb, Zr) and relatively depleted in large ion lithophile elements (such as Sr, Ba). Combined with the published data of Permian sediments at the perimeter of the Yangtze Craton, it is considered that the source area of sediments at the top of Permian Xuanwei Formation experienced strong chemical weathering, and the depositional paleoenvironment was an oxygen-rich freshwater environment. The sediments at the top of Xuanwei Formation not only came from the Emeishan high-Ti basalt transported near the source, but also supplied by the Yangtze Craton. The western margin of the Yangtze Craton was deposited on the active continental margin during the Late Permian.