Abstract: Radioisotopic age determinations targeted at key stratigraphic successions worldwide continue to refine the geological timescale with increasing precision and accuracy and to unravel the tempo of global geological, palaeoclimatic and palaeobiotic processes that have shaped our planet. The last decade has witnessed significant progress in the calibration of the Permian Period through integrated stratigraphic, palaeontological and high-precision geochronological investigations. These studies have largely focused on the Cisuralian and Lopingian stages, particularly the end-Permian mass extinction, whereas much of the Guadalupian and its associated events remain inadequately calibrated. A compilation of the high-precision U–Pb geochronology generated in the past ten years yields ages of 298.92±0.19 Ma for the onset of the Permian, 293.52±0.17 Ma for the base-Sakmarian, 290.10±0.14 Ma for the base-Artinskian, 272.95±0.11 Ma for the Cisuralian–Guadalupian boundary, 265.22±0.34 Ma for the base-Capitanian, 254.14±0.12 Ma for the base-Changhsingian and 251.90±0.10 Ma for the Permian–Triassic boundary. Extension of modern astrochronological methods to the Palaeozoic Era presents new opportunities for broader stratigraphic correlations and enhanced calibration of the Permian timescale. Supplementary material: Table S1 (U–Pb data) is available at https://doi.org/10.6084/m9.figshare.c.3917425

There are at least a dozen Phanerozoic continental flood basalts and oceanic plateaus (large igneous provinces) that roughly obey a “rule of two times one million” (volume of extruded lava of one million cubic kilometers and duration of volcanic activity ~1 m.y.). The correlation between large igneous province ages and mass extinctions (and oceanic anoxia events) is excellent, but quantitative scenarios are still wanting. We hypothesize that the temporal sequences of extrusions determine the severity of extinction: Volcanic pulses separated by thousands of years allow the ocean-atmosphere system time to recover, whereas large volcanic pulses occurring in a shorter sequence may result in a runaway effect and cause a mass extinction. Detailed flow-by-flow magnetic stratigraphies of thick sections have identified directional groups (sequences of superimposed lava flows with the same paleomagnetic direction that cooled in a time too short to record secular variation). With help of this simple tool, many single eruptive events with a volume larger than 1000 km 3 , some in excess of 10,000 km 3 , emplaced in possibly less than a decade, have been identified. We review this evidence, mainly for the following flood basalt provinces: Columbia, Brito-Arctic, Deccan, Karoo-Ferrar, Central Atlantic magmatic province, and Siberian Traps. Large igneous province volcanism occurs in a highly discontinuous way, on embedded time scales, on the order of 10 m.y., 1 m.y., 100 k.y., and 10 yr. This provides constraints for models of plume-lithosphere interaction and magma production. A next step is to model the consequences of massive injection of gases that can be derived from these time and duration estimates. Early attempts are reviewed in a companion paper in this volume.

Geophysical, geological, and petrologic data in southwestern China have been integrated in order to characterize magmatic underplating associated with the Late Permian Emeishan large igneous province (LIP; ca. 260 Ma). Seismic reflection and refraction reveals a heterogeneous crustal structure with high-velocity layers or bodies in the upper crust (6.0–6.6 km/s), lower crust (7.1–7.8 km/s), and upper mantle (8.3–8.6 km/s). These seismically anomalous bodies are all confined in the inner zone of the prevolcanic domal structure, but are generally absent in the intermediate and outer zones. There is a decreasing trend in crustal thickness from the inner zone (>60 km, with a ∼20-km-thick high-velocity lower crust, or HVLC) via the intermediate zone (∼45 km) to the outer zone (<40 km). Because the domal uplift immediately preceding eruption of the Emeishan basalts was unambiguously related to a mantle plume, such a configuration highlights a genetic relationship between the formation of the high-velocity crust and the mantle plume that led to the eruption of the Emeishan basalts. It is proposed that the HVLC may have resulted from magmatic underplating associated with the Emeishan volcanism, whereby the fast mantle represents the residues left after extensive melt extraction from the plume head. Magmatic underplating can also account for the prolonged crustal uplift that formed the Chuandian “old land” in southwestern China. Petrologic modeling further suggests that the HVLC may represent fractionated cumulates from picritic melts and that the Emeishan basalts represent residual melts after polybaric fractionations. This relationship allows a reestimation of the volume of Emeishan magmas, which is as much as 3.8 × 10 6 km 3 , typical of plume-generated LIPs in the world.