Reworking of continental crust on northeastern North China Craton: Evidence from geochronology and geochemistry of Early Cretaceous granitic rocks

Abstract

This paper reports new whole–rock major– and trace–element and zircon UPb and HfO isotopic data for Early Cretaceous granitic rocks on Liaodong Peninsula, NE China, with the aim of constraining continental reworking in the northeastern North China Craton. On the basis of SiO2, MgO, and Sr contents and Sr/Y values, the rocks can be divided into three groups. The low–Mg adakitic rocks show zircon UPb ages of (134–120 Ma), and high SiO2 (67.11–71.14 wt%) and low MgO (0.53–0.62 wt%) contents, and high Sr (531–1108 ppm) contents, Sr/Y (29.3–132) ratios, with enriched Sr–Nd–Hf–O isotopic compositions, indicating an origin of thickened lower mafic crust. The high–Mg adakitic rocks show ages of (126–114 Ma) and are characterized by low SiO2 (53.11–63.88 wt%) and high MgO (2.07–8.93 wt%) contents, and high Sr (391–1041 ppm) contents, Sr/Y (23.9–64.1) ratios, with relatively depleted Sr–Nd–Hf–O isotopic compositions, suggesting that they were derived from partial melting of delaminated lower mafic crust. The normal granitic rocks show ages of (127–121 Ma) and high SiO2 (71.65–77.22 wt%) and low MgO (0.10–0.51 wt%) and Sr (12.1–309 ppm) contents, Sr/Y (0.89–24.5) ratios, with relatively depleted Sr–Nd–Hf–O isotopic compositions, suggesting an origin from lower mafic crust with normal crustal thickness. These constraints, combined with the regional occurrence of A–type granites, bimodal igneous rocks, and metamorphic core complexes, as well as the regional distribution of Mesozoic granitic rocks displaying a younging trend from southeast to northwest for the Jurassic rocks but a reverse trend for the Cretaceous rocks, recorded the roll–back of the Paleo–Pacific plate towards the Eurasian continental margin.