Late Neoarchean granites in the Qixingtai region, western Shandong: Further evidence for the recycling of early Neoarchean juvenile crust in the North China Craton
© 2020 John Wiley & Sons Ltd The Neoarchean basement rocks of the Qixingtai region in the northwest of western Shandong, eastern North China Craton are divided into western and eastern domains, separated by a ductile shear zone. The western domain is mainly composed of early Neoarchean tonalitic and supracrustal rocks, and the eastern domain is composed of late Neoarchean crustally-derived granite with diverse early Neoarchean enclaves up to several kilometres long of supracrustal and gneissic TTG-diorite rocks. This study reports an integrated field, whole-rock geochemistry and zircon U–Pb-Hf study on the granites and their enclaves in the eastern domain. The supracrustal enclaves are mainly composed of meta-basaltic and meta-ultramafic rocks and are the same in lithological association and formation time as the 2,750–2,700 Ma Liuhang “Formation” in the western area. The TTG-diorite enclaves can be divided into early and late groups. Magmatic zircons from early TTG-diorite samples have U–Pb ages of 2,731 ± 17 to 2,748 ± 13 Ma and εHf(t) values of +2.7 to +9.5, whereas trondhjemite samples of the late group have U–Pb zircon ages of 2,588 ± 18 to 2,606 ± 12 Ma and εHf(t) values of +0.6 to +6.5. The Hf isotopic signatures on magmatic zircon from the >2,700 Ma diorite-tonalites indicate that they are predominantly juvenile crustal additions, probably with minor involvement of older crust in their genesis, as given by tDM (Hf) ages ranging back to 2.92 Ga. The eastern granites range from monzogranite to syenogranite in composition and commonly have negative Eu anomalies, indicating residual plagioclase in the source region. Magmatic zircons from two granite samples have U–Pb ages of 2,516 ± 24 and 2,527 ± 18 Ma and εHf(t) values of +1.0 to +7.0. A fine-grained syenogranite dyke contains inherited early Neoarchean zircons with εHf(t) values of +1.6 to +7.4. The isotopic signatures of the late Neoarchean granites that dominate the eastern domain show that they were derived from partial melting recycling of older continental crust recognized in the region – early Neoarchean rocks formed as a result of juvenile crustal additions. This is a common signature for late Archean crustal evolution throughout much of the North China Craton, and is the hallmark of some other Archean terranes, such as the Dharwar Craton of south India. The geodynamic explanations for the formation globally of vast amounts of crustally-derived late Neoarchean granite are discussed.