We present new magnetic and seismic evidence relevant to the hypothesis of a hot spot beneath Yellowstone National Park. A pseudogravity transformation enhances the regional magnetic anomalies, and the resultant map can also be interpreted to show regional variation in geothermal gradient. We propose that a pseudogravity lineament along the eastern margin of the park marks a heat-flow province boundary, whereas closure within Yellowstone marks a crustal hot spot roughly coincident with a double caldera mapped geologically. Magnetic highs at the caldera boundary may represent ring intrusions. Seismically, Yellowstone is at the most active part of the Inter-mountain Seismic Belt, where it changes strike from north to northwest and is intersected by a west-trending secondary seismic belt. Within the caldera, the earthquakes decrease in frequency of occurrence and abruptly decrease in focal depth. At the caldera boundary, four composite fault-plane solutions indicate radial compression, possibly due to resurgent magmatism. These geophysical data support the concept of a roughly circular region of anomalously hot crust at a junction of major tectonic trends but does not directly bear on the hypothesis of a mantle plume.

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