Upper-mantle origin of the Yellowstone hotspot

Abstract

Fundamental features of the geology and tectonic setting of the northeast-propagating Yellowstone hotspot are not explained by a simple deep-mantle plume hypothesis and, within that framework, must be attributed to coincidence or be explained by auxiliary hypotheses. These features include the persistence of basaltic magmatism along the hotspot track, the origin of the hotspot during a regional middle Miocene tectonic reorganization, a similar and coeval zone of northwestward magmatic propagation, the occurrence of both zones of magmatic propagation along a first-order tectonic boundary, and control of the hotspot track by preexisting structures. Seismic imaging provides no evidence for, and several contraindications of, a vertically extensive plume-like structure beneath Yellowstone or a broad trailing plume head beneath the eastern Snake River Plain. The high helium isotope ratios observed at Yellowstone and other hotspots are commonly assumed to arise from the lower mantle, but upper-mantle processes can explain the observations. The available evidence thus renders an upper-mantle origin for the Yellowstone system the preferred model; there is no evidence that the system extends deeper than ϳ200 km, and some evidence that it does not. A model whereby the Yellowstone system reflects feedback between upper-mantle convection and regional lithospheric tectonics is able to explain the observations better than a deep-mantle plume hypothesis.

Helium isotopic composition of hydrothermal fluids from the Manus back-arc Basin, Papua New Guinea

“…The doubts cast over the standard geochemical model by geophysicists is further reinforced by the lack of correlation between high 3 He/ 4 He anomalies and the maximum depth of the plume seismic images (Zhao, 2001;Montelli et al, 2004). That is, whereas some high 3 He/ 4 He values actually correspond to well-resolved deep plumes, others like the Yellowstone hotspot, correspond to regions where a deep origin can be ruled out (Christiansen et al, 2002).…”

Are ‘hot spots’ hot spots?

“…At Yellowstone, volcanics younger than 4 Ma extend for 450 km along the Eastern Snake River Plain, and for 1,000 km in total, from Yellowstone, across the entire northern boundary of the Basin and Range province as far as the Cascades in Oregon [Christiansen et al, 2002].…”

Rheomorphic ignimbrites of the Rogerson Formation, central Snake River plain, USA: record of mid-Miocene rhyolitic explosive eruptions and associated crustal subsidence along the Yellowstone hotspot track

“…1). The volcanism is commonly attributed to a mantle plume beneath the westmigrating North American plate (Armstrong et al 1975;Cathey and Nash 2004;Pierce and Morgan 1992;Coble and Mahood 2012) although slab break-off (James et al 2011) and regional extension in response to upper mantle convection (Christiansen et al 2002) have also been invoked. More than 30,000 km 3 of rhyolites are thought to have been generated due to melting by the incremental emplacement of an elongate ENE-trending, mid-crustal mafic sill at a depth of ∼12 km beneath the Snake River Basin (Rodgers et al 2002;Leeman et al 2008), which crosses numerous N and NWtrending extensional Basin-and-Range faults (Miller et al 1999).…”