Petrogenesis of the 2.3 Ga Lengkou metavolcanic rocks in the North China Craton: Implications for tectonic settings during the magmatic quiescence

Abstract

Paleoproterozoic (~2.3) Ga metavolcanic rocks occur in the Lengkou area, northern Zhongtiao Mountains of the North China Craton (NCC). The area is dominated by metabasic volcanic rocks, intercalated with metamorphosed intermediate to acid volcanic rocks. The Lengkou metavolcanic rocks have a magmatic zircon U-Pb age of 2317 ± 13 Ma, but also contain some 2508 Ma inherited zircons. The Lengkou metabasic and intermediate volcanic rocks are calc-alkaline with high SiO2 and K2O contents. They display fractionation of the HREE relative to the LREE, relative enrichments in large ion lithophile elements and depletion in high field strength elements resulting in negative Nb-Ta-Ti and Zr-Hf anomalies. Therefore, they are inferred to have formed in a volcanic arc setting. The meta-acid volcanic rocks of the Lengkou series have geochemical features similar to the surrounding Sushui Complex (Neoarchaean tonalitic gneiss), resulting from partial melting of ancient crust. The Lengkou metabasic volcanic rocks have a low 143Nd/144Nd ratio and εNd(t) value of 0.8–1.5, with TDM of 2.57–2.63 Ga, indicating the mantle-derived mafic rocks were variably contaminated by older continental material. The integrated data from the Lengkou metavolcanic rocks indicate a convergent subduction-related regime in the early Paleoproterozoic. The isotopic signatures and the xenocrystic zircons demonstrate that subduction occurred at a margin of continental crust, rather than within intra-ocean, exploring an Andean-like setting in the NCC at that time.