Characteristics and geodynamic evolution of Indosinian magmatism in South China: A case study of the Guikeng pluton

Abstract

We examined the geochronology, petrology, and geochemistry of the two-stage Guikeng pluton, Wuyi Mountain Range, South China, with the aim of assessing the influence on Indosinian magmatism in South China of collision/amalgamation between the Sibumasu Block and the Indo-China and South China blocks, and between the North China and Yangtze blocks. An additional aim was to summarise the characteristics and geodynamic evolution of Indosinian magmatism in South China. The Guikeng pluton was then compared with the Indosinian Fucheng–Hongshan and Shiwandashan–Darongshan plutons in the Wuyi–Yunkai Mountain Range Belt, two groups of Indosinian granites in Hunan Province (South China Inland Belt), and Indosinian granitoids in the Sulu–South Korea Belt.The Guikeng pluton consists of medium- to fine-grained biotite monzogranites and biotite granites in its marginal belt, medium- to coarse-grained K-feldspar phenocryst-rich biotite granites in its interior part, and late-stage fine-grained muscovite granites. The granites have high Rb, Cs values, (87Sr/86Sr)i, and Rb/Sr ratios, low Sr, Ba, and εNd(t) values, and slightly to moderately negative Eu anomalies. These geochemical characteristics suggest that the granites were derived from late Paleo-proterozoic meta-sedimentary basement (1.7–2.0Ga).The rocks of the marginal belt and the main part of the pluton originated from two distinct magma sources. The fine-grained muscovite granites were produced by intensive differentiation of K-feldspar phenocryst-rich biotite granites. The granites from the marginal belt and the main part of the pluton yield SHRIMP U–Pb zircon ages of 234±3 and 220.4±3Ma, respectively, consistent with early and late Indosinian magmatism in South China. The early Indosinian metaluminous to weakly peraluminous foliated biotite granites were formed in a collision/compressional setting, whereas late Indosinian strongly peraluminous massive granites were formed in a post-collision setting.The rock assemblage, source region of Indosinian granites, and tectonic setting differ between South China and Sulu–South Korea, indicating the metamorphic basement of the Ogcheon Metamorphic Belt in North China is different to that of the Nanhua Rift in South China.