Geochemistry and zircon U-Pb-Hf isotopes of the late Neoarchean granodiorite-monzogranite-quartz syenite intrusions in the Northern Liaoning Block, North China Craton: Petrogenesis and implications for geodynamic processes

Late Neoarchean weakly foliated to massive granodiorite-monzogranite-quartz syenite intrusions are widely distributed in the Northern Liaoning Block, North China Craton. LA-ICP-MS zircon dating reveals that these rocks were emplaced during 2.56-2.53 Ga and underwent regional metamorphism at similar to 2.51 Ga. These granitoid rocks that contain abundant K-feldspar and high K2O contents with high K2O/Na2O ratios can be subdivided into four lithological types based on their lithological and geochemical characteristics, including porphyritic granodiorites, medium-grained granodiorites, medium-grained monzogranites and porphyritic quartz syenitic gneisses. The porphyritic granodiorites contain biotite as the main mafic mineral, and are characterized by high (La/Yb)N (16-60) and Sr/Y (46-93) ratios, low Yb and Y contents, and weakly positive Eu anomalies for most samples. They also show depletion of Nb, Ta and Ti in the primitive mantle-normalized spidergrams, with zircon epsilon(Hf)(t(2)) values of +3.8 to +6.3, suggesting that they were derived from partial melting of juvenile high-K mafic rocks at the lower crust. The medium-grained granodiorites have major mafic minerals of hornblende and biotite. They display zircon epsilon(Hf)(t(2)) values (+4.6 to +7.5) similar to the porphyritic granodiorites, and have higher CaO contents, molar CaO/(MgO+FeOtot) ratios and Yb, Y contents, with relatively lower (La/Yb)(N) (9-34) and Sr/Y (29-43) ratios for most samples. They show weakly negative Eu and Sr anomalies for most samples, with significant Nb, Ta and Ti depletion, indicating that they might be produced by partial melting of calcalkaline volcanic sources with higher CaO contents at relatively higher levels of the lower crust, compared with the porphyritic granodiorites. The medium-grained monzogranites show the highest Si02 contents (69.71-77.64 wt%), strongly to moderately fractionated REE patterns ((La/Yb)N = 25-69 for most samples), and weakly positive to significantly negative Eu and Sr anomalies, with zircon epsilon(Hf)(t2) values of +2.4 to +4.7, indicating that they may be produced by partial melting of metagreywackes at middle to lower crustal levels. The porphyritic quartz syenitic gneisses exhibit the highest K2O concentrations of 5.11-7.05 wt% and are attributed to the shoshonitic series, and they are featured by high (La/Yb) ratios (34-45), and positive Eu and Sr anomalies, with zero-straddling zircon epsilon(Hf)(t(2)) values (-2.4 to +4.1). We consider that they might be derived from partial melting of a mixed source of juvenile mafic rocks and ancient continental materials in the deep lower crust. Integrating the available data from the previous studies, we conclude that a late Neoarchean active continental margin setting can account for the generation of these granodiorite-monzogranite-quartz syenite intrusions. (C) 2017 Elsevier B.V. All rights reserved.