Chronological, Petrogenetic, and Tectonic Significance of Paleoproterozoic Continental Crust within the North China Craton during the Global Tectono-Magmatic Lull

Abstract

The 2.45–2.20 Ga period during the early Paleoproterozoic era is considered to have witnessed a global “Tectono-Magmatic Lull (TML)” and thus marks a relatively quiescent period. Our study unveils a 2.45–2.20 Ga magmatic suite from the Xiong’ershan area in the southern North China Craton, offering some key constraints on localized active tectonics during the TML. Zircon U-Pb dating shows Paleoproterozoic ages for the meta-basalt (2.31, 2.28 Ga), Na-rich meta-andesite (~2.33 Ga), tonalite-trondhjemite-granodiorite (TTG) gneisses (2.36, 2.30 Ga), K-rich granodiorite (~2.29 Ga), and monzogranite (2.33, 2.27 Ga). The meta-basalts geochemically and petrographically belong to calc-alkaline basalts and show distinctive Nb, Ta, and Ti contents and primitive mantle normalized patterns from different places in the Xiong’ershan area. Combined with their enriched εHf(t) values, the magmas were derived from subduction-related enriched mantle sources within a convergent plate boundary. The meta-andesites display high MgO content (average 4.5 wt%) and Mg# (44–57), strongly fractionated rare-earth pattern, calc-alkaline affinity, and negative Nb, Ta, and Ti anomalies. The TTG gneisses are of high SiO2 type (>62 wt%), high (La/Yb)N (17.5, 39.2), and Sr/Y (50.2, 104.3) and mostly display positive Eu anomalies and high-pressure type. Zircons from these rocks show a relatively narrow range of δ18O isotope values (5.35‰, 6.79‰) with εHf(t) isotope characteristics (−9.3, −3.3), suggesting derivation from partial melting of a thickened mafic lower crust. The youngest K-rich granodiorite and monzogranite show high K2O/Na2O ratios (0.65, 2.45). Variable molar ratio Al2O3/(CaO+Na2O+K2O) (A/CNK) and low zircon εHf(t) values suggest that the K-rich granitoids formed from the partial melting of different levels of crust. The presence of meta-basalt to andesite assemblages and diverse intermediate to felsic magmatic rocks implies magmatic activity within a convergent plate boundary tectonic environment with potential influence from plume-triggered extensional processes, supported by evidence of slab rollback and upwelling of mantle material.