Abstract
AbstractSuper-eruptions are amongst the most extreme events to affect Earth’s surface, but too few examples are known to assess their global role in crustal processes and environmental impact. We demonstrate a robust approach to recognize them at one of the best-preserved intraplate large igneous provinces, leading to the discovery of two new super-eruptions. Each generated huge and unusually hot pyroclastic density currents that sterilized extensive tracts of Idaho and Nevada in the United States. The ca. 8.99 Ma McMullen Creek eruption was magnitude 8.6, larger than the last two major eruptions at Yellowstone (Wyoming). Its volume exceeds 1700 km3, covering ≥12,000 km2. The ca. 8.72 Ma Grey’s Landing eruption was even larger, at magnitude of 8.8 and volume of ≥2800 km3. It covers ≥23,000 km2 and is the largest and hottest documented eruption from the Yellowstone hotspot. The discoveries show the effectiveness of distinguishing and tracing vast deposit sheets by combining trace-element chemistry and mineral compositions with field and paleomagnetic characterization. This approach should lead to more discoveries and size estimates, here and at other provinces. It has increased the number of known super-eruptions from the Yellowstone hotspot, shows that the temporal framework of the magmatic province needs revision, and suggests that the hotspot may be waning.
Highlights
Explosive super-eruptions (≥450 km3; magnitude ≥8; Mason et al, 2004) are landscape-changing extreme events that perturb global climate and devastate environments (Self, 2006)
We report the discovery of two super-eruptions revealed by meticulous correlation of central Snake River Plain (SRP) ignimbrites previously thought to be smaller localized units
We have demonstrated that a multitechnique approach robustly distinguishes between individual eruption units in a succession and enables correlations across tens of thousands of square kilometers to estimate eruption sizes
Summary
Explosive super-eruptions (≥450 km; magnitude ≥8; Mason et al, 2004) are landscape-changing extreme events that perturb global climate and devastate environments (Self, 2006). It correlates with deposits formerly thought to be unrelated at numerous sites along both flanks of the SRP (see Table S1 for previous local names) In the west, it caps all successions, whereas in the east, it overlies the McMullen Creek Ignimbrite, is overlapped by the Castleford Crossing Ignimbrite (Knott et al, 2016a), and proximally is overlain by basalts (Fig. 1). Preferred eruption volume and magnitude estimates are ≥2800 km DRE and 8.8, respectively, which conservatively exclude the distal ash-fall component and assume modest caldera dimensions relative to others in the province (Fig. 1), making it currently the largest documented super-eruption in the province (Fig. 4). The preferred estimate presented above is considered the most geologically reasonable
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