Zirconium isotopes track volcanic inputs during the Permian-Triassic transition in South China

Abstract

The Permian-Triassic mass extinction (PTME), the most severe biocrisis of the Phanerozoic, has been widely attributed to intense volcanism. Although the Siberian Traps Large Igneous Province is regarded as the main trigger of this bioevent, volcanic-arc activity around the margins of the Tethys Ocean may have played a significant role also. Here, we report results of a high-resolution study of zirconium (Zr) isotopes in bulk limestone and volcanic ash beds of the Permian-Triassic transition at Meishan, South China. Mass-dependent fractionation of Zr isotopes, which is controlled by magmatic crystallization, has the potential to differentiate between primitive and evolved igneous sources. The Zr isotopic composition (δ94/90Zr) of volcanic ash in Permian-Triassic transition beds at Meishan is more positive than mantle values, indicating that inputs were probably dominated by regional arc volcanism. The sedimentary beds having the heaviest Zr isotopes during the pre-PTME interval may also record inputs from a felsic volcanic source. A mixing model indicates that the observed negative shift of δ94/90Zr at the PTME horizon was likely due to detrital Zr inputs linked to intensified continental weathering. This study demonstrates that volcanism in South China during the Permian-Triassic transition was linked to regional arc magmatism.