Petrogenesis of the Neoarchean diorite-granite association in the Wangwushan area, southern North China Craton: Implications for continental crust evolution

Abstract

The crustal evolutionary scenarios and geodynamic driving mechanisms of the North China Craton (NCC) during the late Neoarchean (∼2.5 Ga) are still lacking comprehensive understanding due to subsequent strong deformation and metamorphic overprinting events. The widespread ∼2.5 Ga tectono-thermal activities throughout the NCC can be studied to constrain the tectonic evolution at this period. The Wangwushan Neoarchean diorites and high-K granites in the southern NCC were formed at ∼2.52–2.51 Ga. The diorites have high Mg#, Th, Y, low Sr and Sr/Y ratios and variably positive zircon εHf(t) (+2.4 – +8.4) and whole rock εNd(t) values (−0.26 – +3.24), indicating a depleted mantle wedge source which was metasomatized by the melted subducted silicic sediments. The depleted Nb, Ti and enriched LILE and Pb features indicate that the diorites were derived from slightly metasomatized mantle wedge in a subduction-related setting. The high-K granites show a shoshonite affinity and peraluminous features. The rocks have low 10,000 Ga/Al ratios, Zr and Zr + Nb + Ce + Y concentrations, and calculated zircon saturation temperature (TZr = 686–837 °C, 774 °C on average), belong to fractionated I-type granite. Low Sr, Y, flat HREE, and negative Eu anomalies indicate the presence of Ca-rich plagioclase and absence of garnet in the residue during partial melting of the sources, thus further indicating a shallower source with a pressure of <10 kbar and a depth less than 35 km. Zircon Hf and whole-rock Nd isotopic compositions (εHf(t) = −2.7 to +7.4, εNd(t) = +1.25 to +3.09, TDM2 ages are 3.20–2.56 Ga and 3.20–2.65 Ga, respectively) are identical to those of the Neoarchean TTGs, amphibolites and diorites in the Wangwushan area, which likely represent plausible sources for the high-K granites. The partial melting was probably triggered by underplating of mantle-derived mafic magmas in a post-collision setting. Together with 2.57–2.52 Ga TTGs and amphibolites in this area, the magmatic spectrum of these igneous rocks are typical of subduction-related magmatism, involving multi-stage processes in a convergent plate margin, and likely record a transitional regime from early oceanic plate subduction to late post-collisional extension.