Petrogenesis of late Mesozoic granitoids in southern Jilin province, northeastern China: Geochronological, geochemical, and Sr–Nd–Pb isotopic evidence

Abstract

We present geochronological, geochemical, and Sr–Nd–Pb isotope data for late Mesozoic granitoids in southern Jilin province, northeastern China, with the aim of ascertaining the genesis of the granitoids, and further constraining the nature of the lower crust and Mesozoic tectonic evolution of the eastern North China Craton (NCC). The results of LA-ICP-MS zircon U–Pb dating for seven granitoid plutons (from northeast to southwest, the Liudaogou, Toudaogou, Xingfu, Ji'an, Yushulinzi, Lujiangchun, and Zhenjiang plutons) indicate that they formed in the Early Cretaceous (130–122Ma). The granitoids consist of granodiorite, monzogranite, syenogranite, and alkali feldspar granite. Geochemically, they have SiO2=61.8–76.2%, MgO=0.04–3.27%, Mg# [100(Mg/(Mg+Fe2+)]=7–55, and Al2O3=12.7–16.2%, and they are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs, such as Rb, Cs, and K), and depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, such as Nb and Ta). Their initial 87Sr/86Sr ratios, εNd(t) values, and initial 206Pb/204Pb ratios range from 0.70627 to 0.71067 (except for one sample), −1.9 to −13.9, and 17.84 to 18.47, respectively. Compared with the Zhenjiang, Yushulinzi, Lujiangchun, and Ji'an plutons from the southwestern part of the study area [εNd(t)=−9.8 to −13.9 and TDM2=1726–2058Ma], those from the northeastern part of the study area (the Xingfu, Toudaogou, and Liudaogou plutons) have relatively high εNd(t) values (−1.9 to −8.8), low TDM2 (1081–1641Ma). The Early Cretaceous granitoids with high SiO2 contents and low Mg# from the southwestern part of the study area, together with those with high SiO2 contents and low Mg# from the northeastern part of the study area, were possibly mainly derived from the partial melting of Paleoproterozoic lower crust, with a minor contribution from younger material. The latter granitoids, together with the Zhenjiang granodiorites from the southwestern part of the study area, may have formed via mixing between crust- and mantle-derived melts. The rock associations and geochemistry of the southern Jilin granitoids, together with the contemporaneous volcanic rocks in this area, indicate that they formed in an active continental margin setting associated with the oblique subduction of the Paleo-Pacific Plate beneath the Eurasian continent in the Early Cretaceous.