Geochronological and Geochemical Constraints of Chidong Silurian Gabbroic Pluton in Yunkai Domain and Its Tectonic Implications

The geodynamic mechanisms of the Early Paleozoic orogeny in the South China block (SCB) remain highly debated, and two major models involving subduction-collision orogeny and intra-continental orogeny have been proposed. The Early Paleozoic granitic rocks are widely developed in the eastern SCB and the synchronous mafic rocks have recently been reported.However, the petrogenesis of these Early Paleozoic mafic rocks are still controversial, thus hindering our understanding for the Early Paleozoic tectonic setting. In this study, it presents new petrographic, geochronological and geochemical data for the Chidong gabbroic pluton in the Yunkai domain.The representative sample for the gabbric pluton yields a SIMS zircon U-Pb age of 433.9±1.5 Ma (MSWD=0.18). They have SiO₂ of 47.81%-48.83%, MgO of 13.02%-14.65%, Cr of 278×10^-6-356×10^-6 and Ni of 120×10^-6-184×10^-6.They are enriched in large ion lithophile elements with significantly negative Nb-Ta and Ti anomalies.These samples show EMⅡ-like geochemical affinities with high initial ⁸⁷Sr/⁸⁶Sr ratios (0.708 5 to 0.710 7) and low ε_Nd(t) values (-6.0 to -8.2), suggestive of derivation from a paleosubduction-modified wedge beneath the Yunkai Domain. The wedge was undisturbed until Silurian and the Kwangsian igneous rocks in the SCB were associated with the intra-continental orogenism rather than the subduction and subsequent collision.