Petrogenesis of Early Cretaceous granitoids and mafic enclaves from the Jiaodong Peninsula, eastern China: Implications for crust-mantle interaction, tectonic evolution and gold mineralization

Abstract

Early Cretaceous granitic plutons in the Jiaobei Terrane, Eastern China, contain abundant mafic enclaves (MMEs), which are important to understand the tectonic settings and genesis of gold mineralization in the Jiaodong Peninsula. Here, we combine petrology, geochronology, and isotopic geochemistry for MMEs and host granitoids to constrain their tectonic evolution and understand the genesis of coeval gold mineralization in the Jiaodong Peninsula during the Early Cretaceous. Zircon U-Pb dating reveals two magmatic events: (1) the earlier magmatic event (130–126 Ma), represented by Congjia MME (CJ-MMEs) and host granodiorite, and (2) the later magmatic event (121–116 Ma), including Gushan MME (GS-MMEs) and host granite. Field relationship, disequilibrium textures, and elemental and Sr-Nd-Hf isotopic compositions indicate that MMEs and host granitoids formed through mixing/mingling of mafic and felsic magmas. However, significant differences between CJ-MMEs and GS-MMEs indicate that the former has adakitic affinity and was produced by mixing of magmas from lithospheric mantle and mafic lower crust in deep hot zone, whereas the latter has arc-magmatic affinity, suggesting enriched lithospheric mantle source. Higher SiO2 and lower MgO contents in the host granitoids indicate that they were originated from reworking ancient NCC lower crust. Our results reveal crustal growth during the earlier magmatic event, followed by rapid crustal/lithospheric thinning in the later magmatic event, all triggered by ongoing rollback of subducting Paleo-pacific plate. These results combined with complex assemblages of sulfides and volatiles in GS-MMEs indicate that the lithospheric thinning, the rise of enriched lithospheric mantle-derived melts to shallow crustal levels, and crustal-mantle interactions around ∼ 120 ± 3 Ma, are the main factors for massive gold precipitation in the Jiaodong Peninsula.