Petrogenesis of the early-middle Paleozoic granites in northern Wuyi, South China: Implications for the geodynamic process of the Wuyi-Yunkai orogen

Abstract

The Early Paleozoic igneous rocks are extensively distributed across the Cathaysia Block, documenting the Wuyi-Yunkai orogeny in South China. However, the detailed geodynamic process of this orogen remains unclear. To elucidate this tectonic history, we conducted an in-depth investigation of two significant granitic plutons in northern Wuyi. LA-ICP-MS zircon U-Pb dating reveals that the Huangdun pluton was emplaced during the early Silurian (435 – 434 Ma), whereas the Jiaoxi pluton was formed during the early Devonian (401 – 398 Ma). The Huangdun monzogranites characterized by high silica content, predominantly metaluminous to peraluminous nature, low FeO^T/MgO ratios (2.21 – 2.83) and normative-CIPW corundum values (C = 0.48 – 4.72 wt%), closely resembling I–S transformation-type granites. They show relatively low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7053 – 0.7077), ε_Nd(t) values (−6.6 to − 6.2), and zircon ε_Hf(t) values (−6.6 to − 0.6). These geochemical and isotopic signatures suggest that these granites were formed through partial melting of metasedimentary and meta-mafic rocks. In contrast, the Jiaoxi two-mica granites are rich in silica, peraluminous, with elevated FeO^T/MgO ratios (3.94 – 4.98) and high differentiation index values (88.6 – 93.4), indicating their classification as fractionated S-type granites. They display variable ε_Hf(t) values (−15.1 to + 0.6) and low ε_Nd(t) values (−7.0 to − 5.9). These features suggest that they were derived from partial melting of metasedimentary rocks. Integrating these findings with previous research, including the presence of Early Paleozoic MOR-type ophiolites, we propose that the Wuyi-Yunkai orogen as a subduction-collisional orogen. The Huangdun granites were formed during the syn-collisional stage in the early Silurian, while the Jiaoxi granites were generated during the post-collisional extension stage in the early Devonian.