Abstract
The Neoarchean crust-mantle interaction and crustal evolution of the North China craton are controversial and are instructive of the processes of continental crust growth and cratonic evolution. We present here a systematic study of the petrology, geochemistry, and geochronology of Neoarchean granitoids from the eastern North China craton to elucidate their petrogenesis and tectonic setting. The rocks were collected from the Jielingkou, Anziling, and Qinhuangdao plutons, and an amphibole-monzoporphyry dike in the Qinhuangdao pluton. Samples from the Jielingkou pluton, consisting dominantly of monzodiorite and diorite with minor monzonite and granodiorite, contain 52.2–64.4 wt% SiO2, 2.46–4.52 wt% MgO (Mg# = 0.41–0.54), 3.76–5.77 wt% Na2O, and K2O/Na2O ratios of 0.29–0.71. The Anziling pluton samples, comprising syenite and monzonite, display slightly higher SiO2 (60.9–66.7 wt%) and K2O/Na2O ratios (0.70–1.11), but lower MgO (1.54–2.33 wt%) and Mg# (0.40–0.47) values, compared to the Jielingkou rocks. The Qinhuangdao pluton samples, consisting mainly of granite and minor syenite and granodiorite, with some diorite and monzoporphyry dikes, are characterized by the highest SiO2 values (75.7–76.9 wt%) and K2O/Na2O ratios (0.73–1.41) and lowest MgO content (0.14–0.32 wt%) among the studied samples. The amphibole-monzoporphyry dike has intermediate SiO2 (56.3 wt%), high MgO (3.79 wt%), Na2O (5.55 wt%), and Mg# (0.45), and low K2O/Na2O ratio (0.66). Zircon U-Pb laser-ablation–inductively coupled plasma–mass spectrometry dating showed that all plutons have a ca. 2.5 Ga crystallization age. Zircon crystals have mildly positive εHf(t) values (+0.24 to +5.45) and a depleted mantle model age (TDM1) of ca. 2.7 Ga. We interpret the granitoid rocks as sanukitoid-related, Closepet-type granites, potassium-rich adakites, and potassium-rich granitoid rocks that crystallized in the late Neoarchean (2.5 Ga) and were derived from partial melting of mantle peridotite that was metasomatized with the addition of slab melt, thickened alkali-rich juvenile lower crust and juvenile metamorphosed tonalitic rocks. Mantle plume activity ca. 2.7 Ga is thought to have been responsible for the early Neoarchean tectono-thermal event in the eastern North China craton. This activity resulted in a major crustal accretion period in the craton, with subordinate crustal reworking at its margins. A steep subduction regime between ca. 2.55 Ga and ca. 2.48 Ga led to the remelting of older crustal material, with subordinate crustal accretion by magma upwelling from a depleted mantle source resulting in late Neoarchean underplating. This crustal reworking and underplating resulted in the widespread ca. 2.5 Ga plutons in the eastern North China craton. Continental crust growth in the North China craton thus occurred in multiple stages, in response to mantle plume activity, as well as protracted subduction-related granitoid magmatism during the Neoarchean.
Heat- and melt-fluxed melting of lower continental crust: Insights from two types of subduction-related granitoids in northeastern China and the implications for crustal reworking and growth
