Neoproterozoic basic magmatism in the north of Anhui Province: Evidence from whole-rock geochemistry and U-Pb geochronology of Diabase in Langan area

The mafic rock is exposed in North Anhui province of the East China. It consists of diabase, gabro-diabase and dabaseporphyrite. This paper presents a synthetic U-Pb isotopic study of zircons and a whole-rock geochemical study on diabase that were emplaced into the Proterozoic formations in the Langan area of the North Anhui province. The SHRIMP U-Pb zircon dating results indicate that the diabase were emplaced at ca.870-890 Ma. Geochemically, the diabase swarms are characterized by enriched in SiO₂、CaO and (K₂O < Na₂O).It is therefore deduced that the diabases might belong to intraplate tholeiite occurring within the North China Plate. There are also show relative enrichment in LREE and LILE(Rb, Ba and La), a comparative enrichment in Cr and Ni, but a slight depletement in HFSE(Th, Nb, Ta, Zr and Hf).They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams. Taken together, these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Langan area could have been derived from a transitional mantle in the Mesoproterozoic, and were most probably emplaced under a continental margin extensional setting at ca.870-890 Ma. The results of this study demonstrate that the Neoproterozoic magmatism occurred at the Langan area of the North Anhui province, and created conditions for diamond mineralization. Taken along with the Neoproterozoic breakup of the Rodinia Supercontinent and the close relationship between the coeval magmatism and the hypothesis of a superplmue, it is reasonable to contribute the emplacement of the Neoproterozoic diabases in the Langan area to the geochemical fingerprints the contemporaneous mantle plume activity preserved in the continental margin of the North China Block.