Timing and provenance of volcanic fluxes around the Permian-Triassic Boundary Mass Extinction in South China: U-Pb zircon geochronology, volcanic ash geochemistry and mercury isotopes

Abstract

Anomalous mercury (Hg) contents recorded near the Permian-Triassic boundary (PTB) are often linked to Siberian Traps Large Igneous Province (STLIP) volcanism and the Permian-Triassic boundary mass extinction (PTBME). However, mounting evidence indicates that the relation between STLIP volcanism and Hg “anomalies” is not straightforward. This study focuses on the timing and provenance of volcanic fluxes around the PTBME in South China. We constrain carbon isotope (δ13C) and Hg concentration and isotope records by utilizing high-precision U-Pb zircon ages from two expanded deep-water marine sections spanning the Late Permian to Early Triassic in the Nanpanjiang Basin. Results reveal two episodes of Hg enrichment. The oldest episode predates the onset of a large negative δ13C excursion, which is documented to be older than 252.07 ± 0.130 Ma. The second episode occurred between 251.822 ± 0.060 Ma and 251.589 ± 0.062 Ma, coinciding with the nadir of the δ13C excursion. Volcanic ash geochemistry and Hg isotope compositions suggest that mercury was sourced from subduction-related volcanic arc magmatism in the Tethys region, which peaked between 251.668 ± 0.079 Ma and 251.589 ± 0.052 Ma. These results support the hypothesis that regional arc volcanism contributed to the causes of the PTBME in South China and provide evidence that Hg anomalies close to the PTB are not a reliable stratigraphic marker for the PTB extinction event. This study demonstrates that the relations between volcanism, environmental perturbations and mass extinction during the Permian-Triassic transition are better resolved with the aid of high-precision U-Pb zircon ages.

Middle Neoproterozoic (Tonian) Polar Wander of South China: Paleomagnetism and ID‐TIMS U‐Pb Geochronology of the Laoshanya Formation

“…To determine the U‐Pb age of each tuff, we take the youngest cluster of ≥3 analyses, assuming zircons crystallized until the time of eruption and all Pb‐loss is mitigated by the chemical abrasion procedure, in line with previous U‐Pb ID‐TIMS studies which show that youngest date clusters are generally a reliable measure for eruption age (e.g., Edward et al., 2023; Schaltegger et al., 2015). Older dates are assumed to be from recycled zircons or associated with inherited cores, wall rock contamination, and/or prolonged growth in magma chambers.…”

The terrestrial end-Permian mass extinction in the paleotropics postdates the marine extinction

“…The large-scale, frequent felsic volcanism near the South China Block may have forced the ecosystem past this threshold. The felsic volcanism during the earliest Triassic is coincident with the final paleotropical ecosystem collapse in Southwest China and distributed widely in South China and nearby Tethyan regions (20,21,(74)(75)(76). The coeval eruptions of the Siberian Traps may have contributed to the environmental degradation, but they continued for at least 500 ka into the early Triassic (4).…”

“…The emplacement of the SLIP has been the most widely hypothesized trigger of the terrestrial and marine EPME since the early 1990s due to their temporal coincidence (3,5). However, sediments related to felsic volcanism developed extensively along the convergent margins of southern Pangea and around the Tethyan Ocean during the Permian-Triassic transition (21,43,(75)(76)(77) (Fig. 1), introducing another possible stressor for the EPME.…”

Timing and Provenance of Volcanic Fluxes Around the Permian‐Triassic Boundary Mass Extinction in South China: U‐Pb Zircon Geochronology, Volcanic Ash Geochemistry and Mercury Isotopes

“…The data set associated with the current study is available on Zenodo (Edward et al., 2023). Figure 1 was made based on the Panalesis model (Vérard, 2019) using ArcGIS®.…”