Mesoproterozoic (~1.32 Ga) modification of lithospheric mantle beneath the North China craton caused by break-up of the Columbia supercontinent

Abstract

The Mesoproterozoic Yanliao diabase sills are widespread at the northern margin of the eastern North China Craton (NCC) and provide a means to examine the evolution of the NCC lithospheric mantle from amalgamation to breakup and dispersal of the Columbia supercontinent. Here, we report new baddeleyite U–Pb ages, whole-rock geochemical and Sr–Nd–Hf isotopic data, and baddeleyite Hf isotopes for diabase rocks from different sills, which provide insights into the source and petrogenesis of the magmas and the Mesoproterozoic evolution of the NCC. In situ baddeleyite U–Pb dating yields consistent ages of ca. 1320 Ma for these sills, suggesting coeval emplacement. The diabase samples are all tholeiitic and have high TiO2 and total Fe2O3, and low alkali contents. They have variable Mg# values and major- and trace-element contents but uniform primitive-mantle-normalized trace-element patterns, with weak enrichment in light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), and depletion in high-field-strength elements (HFSEs). The whole-rock and in situ isotopic contents of the diabase samples are homogeneous, with initial 87Sr/86Sr ratios of 0.7032–0.7049, εNd(t) values of −0.7 to +3.1, εHf(t) values of +0.8 to +3.7, and baddeleyite εHf(t) values of +1.9 to +7.2. All of these geochemical features suggest that these rocks were derived from high-degree partial melting of a fertile lithospheric mantle source at the depth of spinel stability, with subsequent olivine, clinopyroxene, and plagioclase fractionation. This lithospheric mantle was distinct from the previous Archean to Paleoproterozoic cratonic lithospheric mantle beneath the NCC, indicating a refertilization process by upwelling asthenospheric materials during the Mesoproterozoic. This upwelling, together with other Mesoproterozoic magmatism at the craton margin, would have significantly modified the subcontinental lithospheric mantle of the eastern NCC during the Mesoproterozoic, thereby increasing the susceptibility of the craton to subsequent Mesozoic decratonization.