Neoarchean to Paleoproterozoic continental growth in the southeastern margin of the North China Craton: Geochemical, zircon U–Pb and Hf isotope evidence from the Huoqiu complex

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The Huoqiu complex in the southeastern margin of the North China Craton (NCC) is dominated by Neoarchean gray gneisses, amphibolites and voluminous metasediments. Here we report the occurrence of Neoarchean to Paleoproterozoic rocks from drill-core samples. The gneisses are similar to TTG (tonalite–trondhjemite–granodiorite) in composition and show close spatial association with amphibolites. Geochemical characteristics such as high Sr/Y and (La/Yb)N with steep REE patterns and trace element modeling suggest that these rocks were generated by partial melting of hydrous meta-basalts (amphibolites) at the base of a thickened mafic continental crust, leaving a rutile-bearing eclogite residue. LA-MC-ICP-MS U–Pb age data from magmatic zircon grains show protolith emplacement ages of 2.76–2.71Ga. Subsequently, widespread migmatization took place at 1.91–1.82Ga, generating voluminous migmatites and high-K granites. Hf isotopic compositions of zircon grains from the amphibolite and gneiss show εHf(t) values of 2.4–15.5 and −3.0–1.5, respectively. The tDM2(Hf) model ages of the gneisses range from 2.87 to 3.14Ga, and are identical to the tDM1(Hf) ages of amphibolites (2.84–3.16Ga) within analytical uncertainty, suggesting that the gneisses formed by partial melting of amphibolite, and attest to large-scale reworking of the ancient continental crust during Neoarchean. The zircon grains from the granites define two groups with regard to their Hf isotopic composition. The older group (1916±42Ma) has εHf(t) values and tDM2(Hf) ages of −10.5–2.4 and 2.40–3.20Ga, respectively, whereas the younger one (1823±41Ma) shows a large variation in εHf(t) values ranging from −18.1 to 12.5, with tDM2(Hf) model ages of 1.70–3.59Ga. A couple of zircon grains from the younger group display consistent U–Pb ages and tDM2, indicating accretion of juvenile crust from depleted mantle sources during 1.82 to 1.91Ga. However, the dominant Hf isotope features are consistent with the reworking of preexisting continental crust. We therefore infer that only limited accretion of juvenile crust occurred during this time, and that the Paleoproterozoic (1.82 to 1.91Ga) tectonics in the southeastern margin of the NCC witnessed extensive reworking of older continental crust.