Provenance and weathering as are control on the geochemical composition of the Devonian and Carboniferous sedimentary rocks in the Sudut area, Uvurkhangay Province, Mongolia

Abstract

Major and trace element analyses were made on twenty nine Middle-Upper Devonian and Lower Carboniferous sedimentary rocks from the Sudut area. Negative linear correlation trend on a SiO2-Al2O3 plot and positive correlations of other major oxides with Al2O3 indicates that the proportions of quartz, feldspar and lithics relative to clays is the dominant control on the chemistry of the basement sedimentary rocks. Positive correlations among Al2O3, Zr, Y, Nb, P2O5 and Th suggest that both heavy minerals and clay phases control the abundances of these elements. Major and trace element concentrations in the basement sedimentary rocks suggest a relatively homogeneous source, with felsic composition similar to Upper Continental Crust (UCC). Average Chemical Index of Alteration (CIA) values of the Middle Devonian (58.9), Upper Devonian (53.3), and Lower Carboniferous (54.9) sediments are very low, suggesting weak to moderate weathering of their original source. Middle Devonian sediments were suffered more intense post-depositional K-metasomatism than the Upper Devonian and Lower Carboniferous sediments.