Geochronology and Geochemistry of Paleoproterozoic Granites in Xinyang Area: Implications for Crustal Evolution of Southern North China Craton

The multistage magmatism and metamorphism in the Paleoproterozoic of the southern North China craton (NCC) have recorded the basement and tectonic evolution of the southern NCC. However, the magmatism in Middle-Late Paleoproterozoic were rarely reported. In this paper, it presents a detailed study of petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotope for the Middle-Late Paleoproterozoic granites in the Xinyang area of southern NCC. They include the Panzhuang K-feldspar granite and Chenzhuang biotite K-feldspar granite. The magmatic zircons from them yield the crystallization ages of 1 868 Ma and 1 955 Ma, respectively, indicating that they formed in the Middle-Late Paleoproterozoic. All the studied granites have high SiO₂, and total alkaline, but low CaO, P₂O₅ and MgO contents. Their A/CNK values range from 1.12 to 1.28, suggesting that they are peraluminous rocks. Meanwhile, they show enrichment of LILEs (e.g. Rb, Th and K) but depletion of HFSEs (e.g. Nb, Ta and Ti), Sr and P with moderate to weak negative Eu anomalies. Moreover, the Panzhuang and Chenzhuang plutons have similar zircon ε_Hf(t) values (-0.6-+2.6), with the two-stage Hf model ages (T_crust) ranging in 2.40-2.64 Ga. All of these evidences indicate that the Late Archean to Early Paleoproterozoic crust in the Xinyang area were strongly modified in Middle-Late Paleoproterozoic. Combined with the records of magmatism and metamorphic events in the southern margin of the NCC, it is suggested that the formation of the granites in the Xinyang area may be related to the collision between the eastern and western blocks of NCC. Furthermore, the frequent Paleoproterozoic magmatic activities (2.24-1.85 Ga) in this area probably resulted from an eastward-directed subduction of an ancient ocean between the eastern and western blocks, and the western block.