High-precision U/Pb geochronology of large igneous provinces and mass extinctions : testing coincidence and causation

Abstract

The history of life on Earth is punctuated by mass extinction, the cause of which has often been attributed to rapid changes in global climate and/or ocean chemistry that are inferred to accompany the eruption of large igneous provinces (LIPs). Implicating LIP eruptions as the trigger of the biologic crises has relied on the approximate coincidence in time between these two events. To test this causal link and to understand the mechanisms driving extinction requires a more accurate and precise temporal record of both events than currently exists. With higher precision, the ability to resolve the relative timing of mass extinction and magmatism outside the analytical uncertainty on dates populating age models is possible, allowing detailed investigation of a causal connection. The current work develops zircon and perovskite minerals as accurate, high-precision geochronometers on the mafic rocks that commonly characterize LIP magmas. These advances are coupled with the latest techniques in U/Pb geochronology to generate highprecision age models which are used to evaluate the relative timing of (1) the end- Permian mass extinction, which is the most severe in the Phanerozoic, and the Siberian Traps LIP, which is the largest continental magmatic event in the Phanerozoic, and (2) the Karoo-Ferrar LIP and the early-Jurassic biotic crisis and global ocean anoxia. With these datasets, age-models for both mass extinction and LIP magmatism precise to a maximum of ~0.02% are developed, enabling, for the first time, resolution of the relative timing of eruption and extinction outside of uncertainty. This work conclusively indicates that (1) Siberian Traps LIP magmatism precedes onset of the end-Permian mass extinction and continued through the mass extinction interval, into the early Triassic biotic recovery interval, and (2) Karoo-Ferrar LIP magmatism likely preceded the onset of early-Jurassic extinction and ocean anoxic event and continued through this interval, over ~ 1 Ma.