Neoarchean-Paleoproterozoic tectonic evolution of the southern margin of the North China Craton: Insights from geochemical and zircon U–Pb–Hf–O isotopic study of metavolcanic rocks in the Dengfeng complex

Abstract

Neoarchean magmatic rocks are widespread in the North China Craton (NCC). But the tectonic setting of these Neoarchean rocks is still controversial. The Dengfeng Complex in the southern segment of the NCC contains a typical suite of early Precambrian metamorphic rocks including massive Neoarchean metavolcanic rocks, which are important recorders of the early geodynamic setting and crustal evolution of NCC. In this study, we examine the geochemical and zircon U-Pb-Hf-O isotopic signatures of the Neoarchean metavolcanic rocks (amphibolite, biotite leptynite and leptite) from the Dengfeng Complex, with a focus on rocks from the understudied Jishan area together with rocks from the Songshan area for comparison, to constrain the petrogenesis of these rocks and further infer the geochronological framework, tectonic setting and crustal evolution of the southern NCC.The studied amphibolites are characterized by high Mg#, and enrichments in LREE, Rb, K and Pb. Their zircons show positive εHf(t) values and mostly high δ18O values (6.0–7.5‰). All these features indicate that they were most likely derived from a mantle wedge that was modified by components from low-temperature altered oceanic crust. SIMS zircon U–Pb isotopic dating reveals that the protoliths of the amphibolites were emplaced from as early as 2.83 Ga to 2.51 Ga, and underwent two metamorphic events at 2.48 Ga and 1.92 Ga, respectively. The studied felsic metavolcanic rocks are characterized by low Mg# values, enrichments in LREE, K, Rb and Pb, depletions in Nb, Ta and Ti, and various negative Eu anomalies. Their zircons display positive εHf(t) and mantle-like δ18O values. All these features suggest that they were mainly derived from partial melting of juvenile crustal components. SIMS zircon U–Pb isotopic dating indicates the felsic metavolcanic rocks erupted at 2.54–2.53 Ga. No zircon overgrowth was observed in these volcanic rocks during later metamorphic events. Based on these new data, we proposed a new tectonic model for the Neoarchean tectonic evolution of the southern margin of the NCC with tight constraints on the timing from subduction (at least 2.54 Ga) to collision (2.48 Ga).