Testing Magnetotelluric Constraints on the Physical State of the Yellowstone Plume

Abstract:

Recent inversions of long-period magnetotelluric (MT) datasets (Kelbert et al., 2012; Meqbel et al., 2014) have suggested that the mantle lithosphere directly beneath the modern Yellowstone caldera is electrically resistive. This observation implies that the uppermost mantle does not contain significant quantities of melt and therefore seems to contradict seismic tomography studies that find a major low-velocity plume-like feature directly beneath Yellowstone. Our ongoing investigation of the long-period Earthscope MT data suggests that these data are relatively insensitive to the conductivity structure in the upper mantle due to screening of deeper features by the modern electrically conductive magma chamber(s). Hence, at present we cannot conclude that the uppermost mantle directly beneath Yellowstone is electrically resistive. However, we do resolve a major electrically conductive anomaly that dips generally to the west at approximately 30 degrees from the vicinity of the seismically imaged magma reservoir(s) beneath the Yellowstone. The MT data therefore may indicate that the flow of melt is at least partially influenced by structures to the west of the modern caldera, specifically ancient (Paleoproterozoic) structures at the edge of the Wyoming Craton. While the geochemistry of Yellowstone eruptive products remains ambiguous with regards to source, radiogenic isotope model ages could be interpreted as supporting this possibility.