Geochemical characteristics of Linxi Formation along Taohaiyingzi section in Ar Horqin Banner, Inner Mongolia, and the constraint on the provenances and the tectonic settings

A set of thick-bedded dark muds and shales are developed in Linxi Formation of Upper Permian in south-central part of Da Hinggan Mountains, serving as one of the important Upper Paleozoic hydrocarbon source rock strata in this region. The Taohaiyingzi section in Ar Horqin Banner is one of the most typical sections of Linxi Formation, and the authors took the section as the study area. Test and analysis of major elements, trace elements and rare earth elements were conducted for ten pieces of sand or mud samples of Linxi Formation along the section. The results of element analysis and the diagrams of provenance discrimination function (F₁-F₂), Ni-TiO₂ and La/Th-Hf show that Linxi Formation along the section had several provenances, which mainly included felsic igneous rock provenance and quartzite sedimentary provenance besides a minority of intermediate-basic igneous provenance. Based on the analysis of the spider diagram of trace elements standardized by PAAS, the distribution pattern of rare earth elements standardized by chondrite, the diagrams of K₂O/Na₂O-SiO₂, Zr/Th and TiO₂-TFe₂O₃+MgO and provenance tectonic setting discrimination function (F₁-F₂)'of the samples of the section, and the sand geochemical parameter contrast between the samples and different tectonic settings, the authors hold that the provenances of Linxi Formation along the section exhibited complex tectonic settings with the characteristics of passive continental margin, active continental margin and continental island arc. The comprehensive analysis shows that the provenances of Linxi Formation of the section consisted of igneous rocks and quartziferous sedimentary rocks under the passive continental margin background, and igneous rocks under the active continental margin and continental island arc background. Combined with the previous related study achievements, it could be concluded that the sedimentary formations of Late Carboniferous to Permian magmatic passive continental margin under extension background and Paleozoic arc magmatic rocks under subduction background in Xing'an-Mongolian Orogenic belt ought to be the primary provenances of Linxi Formation along the section.