Late Neoarchean potassic high Ba–Sr granites in the Taishan granite–greenstone terrane: Petrogenesis and implications for continental crustal evolution

Abstract

A series of Late Neoarchean high Ba–Sr granites with a potassium-rich signature has been identified from the Taishan granite–greenstone terrane (TSGT), within the Eastern Block of the North China Craton (NCC). LA-ICP-MS zircon dating shows that the Wanghailou, Hujiazhuang and Xiajiazhuang granitic intrusions were emplaced at ~2.54Ga, ~2.52Ga and ~2.47Ga, respectively. Geochemically, they are alkali-rich, with high K2O contents and high K2O/Na2O ratios, revealing their high-potassium calc-alkaline nature. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to typical A-, I- and S-type granites, and show negative anomalies in HFSE (Nb, Ta, Ti) and weak Eu anomalies. Their geochemical and isotopic characteristics, such as extremely low Y and Yb concentrations, high Sr/Y and (La/Yb)cn ratios, strongly fractionated REE patterns and elevated εNd(t) and εHf(t), imply that the parental magmas were derived directly from partial melting of the sub-arc enriched mantle at depths >15kbar with residual garnet in the source. This mantle was previously depleted lithospheric mantle and was subsequently metasomatized by subduction-related fluids and/or melts. Fractional crystallization and crustal assimilation of these magmas during ascent resulted in their variable geochemical and isotopic characteristics. Taking into account the space–time patterns of late Archean magmatism in the area, an active subduction regime is favored to account for the generation of these potassic high Ba–Sr granites in the TSGT.The two-stage Nd and Hf model ages of these granites suggest that continental crust older than 2.80Ga is preserved beneath the TSGT. In combination with previous data from the region, it is noted that, apart from rapid crustal growth at ~2.7Ga, other additions of mantle-derived magma, such as minor 2.6–2.5Ga sanukitoids, siliceous high-Mg basalts (SHMBs) and high Ba–Sr granites, also made a significant contribution to continental crustal evolution in the TSGT.