Neoarchean sanukitoids and associated rocks from the Tengzhou-Pingyi intrusive complex, North China Craton: Insights into petrogenesis and crust-mantle interactions

Abstract

Quartz monzodiorites, granodiorites and monzogranites constitute the dominant lithological assemblage in the Neoarchean Tengzhou-Pingyi intrusive complex (TPIC) in the southwestern part of western Shandong Province (WSP) in the eastern part of the North China Craton (NCC), and mafic magmatic enclaves (MMEs) are widely developed only in granodiorites of the TPIC. LA–ICP–MS zircon U-Pb isotopic dating reveals that the TPIC was emplaced at ~2.54–2.52 Ga. The ~2.54 Ga monzogranites display geochemical affinities with high-K granites, and they were likely derived from the partial melting of metamorphic greywackes at lower crustal levels. The ~2.54–2.52 Ga quartz monzodiorites and granodiorites show significant geochemical similarities to the Archean sanukitoids of the western Karelian Province of Finland with higher Mg# (43–57) values, Cr (24–88 ppm), Sr (547–1154 ppm), and Ba (662–1961 ppm) contents and K2O/Na2O (0.42–1.00) ratios. Therefore, we define the quartz monzodiorites and granodiorites as Neoarchean sanukitoids. Based on their lithological assemblages and geochemical characteristics, these sanukitoids can be subdivided into sanukitoid quartz monzodiorites (SQMs) and porphyritic sanukitoid granodiorites (PSGs). The SQMs exhibit higher positive ɛHf(t2) values from +1.9 to +3.6 with TDM values of 2.70 to 2.77 Ga and are strongly enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), implying a mantle source that was enriched by either fluids or melts. The PSGs have a wide range of ɛHf(t2) values from −3.4 to +3.8, suggesting that they were formed by crust-mantle magma mixing. This interpretation is also supported by the petrological textural and compositional disequilibrium of plagioclase phenocrysts from the PSGs. Moreover, the MMEs and their host PSGs have identical crystallization ages (~2.54 Ga), similar mineral chemistries and zircon Lu-Hf isotopic compositions, indicating that the MMEs are cumulates from the earlier host PSGs magma. Petrogenetic studies and zircon Lu-Hf isotopic features of these lithological assemblages indicate that the interval of ~2.55–2.52 Ga in the TPIC represents an important period of crustal growth and crust-mantle interactions. Considering the spatial-temporal relationships and the petrogenesis of the diverse lithological assemblages, we propose that the Neoarchean TPIC was most likely formed in an active continental margin setting.