Ascertaining the origin of magmas for the 1.32 Ga Yanliao mafic sills: An elemental and Os-Nd isotope perspective

Mafic sills witness the evolution of magma and can serve as a sensitive indicator of tectonic regimes. The elemental and isotopic characteristics of mafic sills are crucial for ascertaining the petrogenesis and understanding their tectonic implications. Here, we present new baddeleyite and zircon U-Pb ages, whole-rock geochemical and Os-Nd isotopic data for the 1.32 Ga Yanliao mafic sills from the northeastern North China Craton. The SIMS baddeleyite and LA-ICP-MS zircon dating yields the ²⁰⁷Pb/²⁰⁶Pb ages of 1329 ± 8 to 1303 ± 7 Ma, serving as an epitome of the Mesoproterozoic magmatic event of the North China Craton. The diabases exhibit low SiO₂ and variable Mg^# (Mg^#=Mg²⁺/(Mg²⁺+Fe²⁺) in molar), belonging to subalkaline series with high-Fe tholeiitic affinities. They are abundant in LREE, Pb and LILEs (Rb, Th, and U), depleted in HFSEs (Nb and Ta) and endowed with enriched mantle geochemical peculiarities. The simulations of Nd and Os isotopes indicate the mafic rocks have undergone slight crustal contamination (ca. 4–9 %) during magma ascent. The correlations among V, Ni, and Cr contents suggest the clinopyroxene fractionation in the magma evolution. The incompatible-element ratios and ɛ_Nd(t) reveal that the Yanliao mafic sills were predominantly derived from the subcontinental lithospheric mantle, with a minor contribution from the asthenospheric or mantle plume source. Their parental magmas are modeled to have originated from approximately 10 % partial melting of spinel-bearing garnet lherzolite, representing the melting traits of the contemporaneous subcontinental lithospheric mantle. Coupled with other geological data, it is suggested that the diabases from the Yanliao mafic sills have witnessed the episode of the plume and/or asthenosphere upwelling at ca. 1.32 Ga. The vertical mantle upwelling regimes heated and facilitated the partial melting of the enriched lithospheric mantle, resulting in the mafic magmatism in North China Craton during the Mesoproterozoic.