Geochemical and Detrital-Zircon U–Pb Constraints on the Provenance of the Taiyuan Formation Bauxitic Succession in Longdong, Ordos Basin

Abstract

Recent exploration of the Taiyuan Formation bauxitic succession in Longdong has highlighted the need to discriminate between the local carbonate-residue and external aluminosilicate-supply models. However, these alternatives have rarely been tested in Longdong by jointly assessing the compositional viability of carbonate residues and the geochemical–geochronological correspondence between the bauxitic succession and candidate external source regions. Major-, trace-, and rare-earth-element data from wells DLF7, THF4, and THS7 were integrated with 203 detrital-zircon U–Pb ages from two samples and regional tectono-paleogeographic evidence. Immobile-element systematics indicate derivation mainly from calc-alkaline intermediate–felsic igneous rocks and related metamorphic rocks. Weathered fractions calculated for North Qinling granitoids and Taihua Group metamorphic rocks show major-element affinities with Taiyuan Formation claystone, whereas the Si–Al compositions of calculated insoluble residues from the underlying limestone and dolostone are inconsistent with a dominant source role for these carbonate rocks. Trace-element and REE patterns likewise show closer affinities with felsic upper-crustal rocks than with the underlying carbonates. Detrital zircons define prominent age components at ca. 470–400 Ma, ca. 1000 Ma, and ca. 2500 Ma; the dominant ca. 470–400 Ma component corresponds closely to Caledonian magmatism in North Qinling. The aluminosilicate material incorporated into the Taiyuan Formation bauxitic succession was therefore derived predominantly from weathering products of multistage igneous–metamorphic terranes in North Qinling, whereas ancient basement along the southern margin of the North China Craton may have provided subordinate components.