Yellowstone Hotspot: Insights from Magnetotelluric Data

Yellowstone Hotspot: Insights from Magnetotelluric Data Electrical conductivity model at 50 km depth beneath Snake River Plain. Data locations are indicated by black triangles. The direction of absolute motion of North American plate is marked with a white arrow. Also schematically indicated are the “tectonic parabola” around the Eastern Snake River Plain, and the Yellowstone National Park (black oval). The grey lines are the transects shown in detail in Figure 2.
We have performed a set of three dimensional inversions of magnetotelluric (MT) data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from USArray MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). The images reveal extensive areas of high conductivity in the upper mantle and lower crust beneath Yellowstone and the SRP. A highly conductive (~ 1 S/m) shallow anomaly directly beneath the Yellowstone caldera extends to no more than 20 km depth (Figure 2a), but connects to a deeper (40-100 km) conductive feature in the mantle that extends at least 200 km southwest (Figure 1a) roughly parallel to the direction of North America absolute motion. In several locations beneath the Eastern SRP very high conductivities (a few S/m) are imaged at or near the base of the lower crust (Figures 2b, c).
</p><p>The lateral spatial extent of the mantle conductive anomalies correlates well with low velocity anomalies in the upper mantle imaged teleseismically [e.g., Humphreys et al, 2000; Smith et al, 2009], and with surface wave tomography [Schutt et al., 2008]. We see little evidence for a deep narrow plume extending directly beneath Yellowstone, although conductivities remain elevated to depths of at least 200 km over a broad area in the vicinity of the putative hotspot. Plausibly the seismically imaged thermal anomaly is present, but poorly resolved by the MT data, which is much more strongly impacted by partial melt and fluids present at shallower depths. Overall our images are quite consistent with interpretations that emphasize the role of local convection and lithospheric interaction to explain patterns of progressive magmatism along the Yellowstone “hot spot” track [e.g., Humphreys et al, 2000]. High conductivites imaged at the base of the crust beneath the Eastern SRP are probably due to a combination of partial melt, and highly saline fluids exsolved during magmatic underplating.
</p><p>Humphreys, E.; Dueker, K.; Schutt, D. & Smith, R. (2000), 'Beneath Yellowstone: evaluating plume and nonplume models using teleseismic images of the upper mantle', GSA Today, 10, 1-7.
</p><p>Smith, R.B.; Jordan, M.; Steinberger, B.; Puskas, C.M.; Farrell, J.; Waite, G.P.; Husen, S.; Chang, W. & O'Connell, R. (2009), 'Geodynamics of the Yellowstone hotspot and mantle plume: Seismic and GPS imaging, kinematics, and mantle flow', J. Volcanol. Geoth. Res. 188(1-3), 26 - 56.
</p><p>Schutt, D.; Dueker, K. & Yuan, H. (2008), ‘Crust and upper mantle velocity structure of the Yellowstone hot spot and surroundings’, J. Geophys. Res. (Solid Earth), 113, 3310-.
</p><p>Acknowledgements: Support from the US DOE under grant DE-FG02-06ER15819 for development of the 3D inversion code is acknowledged.</p>


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