Calibrating Archean and Miocene large igneous province emplacement and geologic timescales with high-precision U-Pb geochronology

Abstract

In the past decade, methodological advances in the precision and accuracy of geochronology have improved estimates of the timing and duration of large igneous province (LIP) emplacement, mass extinction events, and global climate perturbations, and in general have supported a temporal link between them. In this thesis, I use high-precision U-Pb ID-TIMS zircon geochronology to present new temporal constraints on Earth’s oldest and youngest LIPs.

By integrating paleomagnetism and geochronology into a detailed stratigraphic study of two intervals of flood basalt volcanism in the Neoarchean Fortescue Group (Western Australia), I provide temporal constraints on rapid plate motion at 2.7 Ga, and the timing of Earth’s oldest documented magnetic field reversal. I then apply U-Pb zircon geochronology to the Miocene Columbia River Basalt Group (Northwest USA), Earth’s youngest LIP, and show that it erupted in ~750 ka, 2.4 times faster than previously thought, with its largest formation emplaced in ~500 ka. The new age model provides estimates for a constant eruptive flux through the main phase of volcanism, the timing of Miocene magnetic field reversals during a poorly calibrated interval of the Geomagnetic Polarity Timescale, and stronger temporal evidence for a correlation between the beginning of LIP volcanism and the onset of the Miocene Climate Optimum (MCO), an interval of global warming and elevated atmospheric carbon dioxide.

Age models for the MCO and other paleoclimate events in the sedimentary record are often calibrated by biostratigraphy and magnetostratigraphy rather than absolute geochronology, which may hinder their correlation to high-precision eruptive timelines for LIPs. I present a case study from the Early Miocene Bisciaro Formation (Italy) to show the importance of radiometric calibration of sedimentary records where astronomical tuning is not possible, to address inadequacies in traditional methods of age calibration.

Finally, I review existing high-precision geochronology from 12 LIPs and their corresponding extinction or climate events, to begin to assess if advances in geochronology support a causal relationship between them. Despite much progress, higher precision geochronology of both LIPs and environmental records will be required to further understand how these catastrophic volcanic events have changed the course of our planet’s surface evolution.