Abstract

The composition of the lower crust is a key factor in understanding tectonic activity and deformation within the Earth. In particular, the presence or absence of melt or fluids has strong control on tectonic evolution. Multi-physics inversion results from the western United States demonstrate that tectonic inheritance plays a much stronger role in determining the location of melt in the lower crust than previously thought. Even in a currently active area such as the Yellowstone Hotspot, fluid dominated structures and fluid free regions are juxtaposed. This is incompatible with the commonly used model of recent tectonic activity as a main controlling factor for the presence of fluids or melt. These results have global implications for how geophysical models are interpreted and how they can be related to geodynamic simulations.