The late Early-Paleozoic granitic magmatism in Northwestern Fujian, China: constraints on intraplate orogeny in the South China block

Abstract

The Early Paleozoic tectono-thermal event was a significant orogenic activity during the Phanerozoic era, which had a profound impact on the early crust of the South China Block (SCB) and established the foundation for later tectonic activity. The Wuyi-Yunkai orogenic belt in Southeastern China was extensively exposed to Early Paleozoic magmatism, the genetic mechanism of which remains controversial. To shed light on this issue, detailed petrological, geochemical, and zircon U–Pb–Hf isotopic studies were carried out on two granitoids, namely the Yuntongshan pluton and the Gaoqiao pluton, identified in the central Wuyishan. Zircon U–Pb chronology of the Yuntongshan and Gaoqiao bodies yielded ages of 437 ± 4 Ma (MSWD = 2.2) and 404 ± 2 Ma (MSWD = 12), respectively, indicating that they were emplaced during the Early Silurian and Early Devonian periods. These granitoids are primarily composed of biotite-granite and biotite-monzonitic-granites, with high concentrations of S_iO₂ (73.59–75.91 wt%), K₂O + Na₂O (8.31–8.73 wt%), and low contents of MgO, CaO, Cr, Ni. They are classified as high-K calc-alkaline and weakly metaluminous-strongly peraluminous S-type granites. These granitoids are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. The εHf(t) values of − 3.3 to − 15.4 with two-stage Hf model ages ranging from 2829 to 1644 Ma, combined with the presence of Neoproterozoic inherited zircons, suggest that the primary magma of these granitoids was derived from the partial melting of Neoproterozoic crust with a Paleoproterozoic crustal model age. These findings, combined with the spatio-temporal distribution of regional magmatism, reveal that the late Early-Paleozoic granitoids formed in the intraplate orogenic background originating from the subduction of the proto-Tethys Ocean and proto-Pacific Ocean around the margin of the east Gondwana supercontinent.