Complex Neoarchean mantle metasomatism: Evidence from sanukitoid diorites-monzodiorites-granodiorites in the northeastern North China Craton

Abstract

Mantle metasomatism is a major factor leading to diverse arc magmatism. Late Neoarchean sanukitoid diorites-quartz diorites-monzodiorites-granodiorites (DQMGs) are widespread in the North Liaoning Block, northeastern North China Craton, and were evidently emplaced into Neoarchean tonalite-trondhjemite-granodiorite (TTG) gneisses and metamorphic calc-alkaline volcanic rocks. Integrated with these slightly earlier arc-related TTGs and volcanic rocks, DQMG magmatism may preserve crucial signatures of complicated Neoarchean mantle metasomatism.These DQMGs show emplacement ages of ~2.56 to 2.53 Ga and wide ranges of SiO2 (51.34–68.74 wt%), K2O (1.67–4.56 wt%), MgO (1.48–6.68 wt%), Cr (29–334 ppm) and V (46–329 ppm) concentrations and high Mg# values of 45 to 65, with zircon ɛHf(t2) values from +0.0 to +6.9, suggesting that the DQMGs are typical Archean sanukitoids. According to geochemical characteristics and petrogenesis, these sanukitoid DQMGs are subdivided into Group #1 and Group #2. The Group #1 magma was derived from partial melting of a fluid-metasomatized mantle source altered further by adakitic melts, and the Group #2 magma from the mantle source was further metasomatized by subducted sediment melts. The relatively high K2O contents, K2O/Na2O, Nb/Zr ratios and various TDM(Hf) values of the sanukitoid DQMGs were derived from a lithospheric mantle source that was metasomatized by subducted fluids, slab- and sediment-derived melts. Therefore, the complex mantle metasomatism may be an essential reason for the appearance of a mass of K-rich granitoids with sanukitoid composition and the Neoarchean diversity of granitoid rocks.