Geochronological and geochemical studies on the granitoid gneisses in the northeastern North China Craton: Insights into the late Neoarchean magmatism and crustal evolution

Abstract

Granitoid gneisses, including TTG and granitic gneisses, are important components of the Archean continental crust and can provide significant clues to crustal growth and geodynamic setting. The granitoid gneisses in Southern Jilin Province (SJP) were formed at 2496–2513 Ma, which experienced the late Neoarchean metamorphism. Zircon Hf isotopes indicate that the ∼2.5 Ga granitoid magma in SJP was mainly originated from the remelting of 2.7–3.0 Ga crust. In combination with other Hf isotopic data from previous studies, it is suggested that the major crustal growth period in SJP is 2.7–2.8 Ga with subordinate mantle extraction at ∼3.0 Ga. According to the mineralogical and geochemical features, the granitoid gneisses in SJP can be divided into three groups: high-Mg group (HMG) TTG gneisses, low-Mg group (LMG) TTG gneisses and granitic gneisses. Most of the HMG TTG gneisses are characterized by high Sr and low Y contents, negligible negative Eu anomalies, LREE enrichment, HREE depletion, flat MREE-HREE patterns, and superchondritic Nb/Ta ratios, suggesting that they were derived from polybaric melting with residues of garnet-amphibolite and rutile-eclogite (melting depths >45–60 km). However, the geochemical features of the LMG TTG gneisses together with published experimental studies suggest that they were formed by partial melting of basaltic rocks with minor felsic crust material inputs. In addition, garnet amphibolite residue and plagioclase accumulation were involved in the formation process of the LMG TTGs, which were generated at shallower depths (45 ≤ D < 60 km). High Mg# values, Cr and Ni contents and other evidence together indicate possible generation of HMG TTGs by partial melting of subducted slab. Furthermore, their large ranges of εHf(t) values (−1.36 to +4.98) and TDM2 ages (2727–3067 Ma) are consistent with those of continental arc model. In contrast with HMG TTGs, the LMG TTG gneisses display low Mg# values, Cr and Ni contents and more evolved zircon Hf isotopes, indicating derivation from melting of the thickened lower crust. The granitic gneisses were presumably generated by melting of variable contributions of TTGs and metasedimentary rocks in a subduction-related setting. Combined with other studies, it is proposed that extensive subduction-related magmatic rocks possibly existed during the late Neoarchean all over the world.