资源环境科技发展态势分析平台

Geophysical imaging of the Yellowstone supervolcano shows a broad zone of partial melt interrupted by an amagmatic gap at depths of 15-20 km. We reproduce this structure through a series of regional-scale magmatic-thermomechanical forward models which assume that magmatic dikes stall at rheologic discontinuities in the crust. We find that basaltic magmas accumulate at the Moho and at the brittle-ductile transition, which naturally forms at depths of 5-10 km. This leads to the development of a 10- to 15-km thick midcrustal sill complex with a top at a depth of approximately 10 km, consistent with geophysical observations of the pre-Yellowstone hot spot track. We show a linear relationship between melting rates in the mantle and rhyolite eruption rates along the hot spot track. Finally, melt production rates from our models suggest that the Yellowstone plume is similar to 175 degrees C hotter than the surrounding mantle and that the thickness of the overlying lithosphere is similar to 80 km.

Plain Language Summary We present a series of supercomputer models which we use to investigate the origins of the two-level magmatic system revealed by recent geophysical observations of the Yellowstone supervolcano. We show that the distribution of melt which matches these observations arises when we assume that rising magmas preferentially accumulate at depths where there are strong contrasts in the ratio of melt overpressure to the effective viscosity of the surrounding crust. Melt accumulates at the major rock strength discontinuities which occur at the base of the crust and at the brittle-ductile transition which forms above the developing magmatic system at approximately 10-km depth. This second boundary captures the considerable majority of the melt and produces a basaltic sill complex which resides between depths of 10 and 25 km and which provides heat which melts the surrounding crust. This sill complex cools and solidifies and separates the partially molten crust above and below it into the two magmatic systems seen in the geophysical images. Finally, we are able to constrain the temperature of the Yellowstone mantle plume to be 175 degrees C hotter than the surrounding mantle and the thickness of the overlying lithosphere to be approximately 80 km.