Geochronology, petrogenesis and oxidation state of the Wenyu igneous suite in the Xiaoqinling district, North China Craton: Implications for lithospheric thinning and magma fertility

Abstract

Recent studies have shown that the Mesozoic metallogenic event in the southern margin of the North China Craton (NCC) is related to the coeval magma activities generated by the lithospheric thinning and asthenosphere upwelling. However, the reason why some Mesozoic magmatic systems in this area are barren is not clear. In this study, we report new geochronological and geochemical data for a Mesozoic igneous suite of Wenyu monzogranites from the Xiaoqinling area in the southern margin of the NCC, focusing on the petrogenesis and oxidation state with their implications on lithospheric thinning and magma fertility. The Wenyu monzogranites have zircon UPb ages between 141.4 and 122.2 Ma. Whole-rock major and trace element, SrNd and zircon Hf isotope geochemistry suggest that the Wenyu monzogranites were dominantly derived from partial melting of the metamorphic and volcanic rocks from the Neoarchean to Paleoproterozoic, with potential replenishments of mantle-derived magmas triggered by the lithospheric thinning and hot asthenosphere upwelling. Zircon trace element geochemistry suggests a low oxidation state for the Wenyu magmatic system, which probably resulted in early sulfide saturation. Most of the ore-forming chalcophile elements (Au and Cu) were locked in a sulfide phase that was retained in cumulate rocks at depth due to the early sulfide saturation, so that when the magma became fluid saturated at the later stage of magmatic evolution, it did not have access to the Au and Cu. As a consequence, our study suggests that the Wenyu pluton was not prospective for magmatic-hydrothermal Au ± Cu deposits.