Spatiotemporal Evolution of Volcanism in the Black Rock Desert Volcanic Field, Utah, and Its Migration Relative to the Colorado Plateau

Abstract

In the southwest USA, the Colorado Plateau is encircled by Late Cenozoic volcanic fields, most of which have eruptive histories that are marginally constrained. Establishing the spatiotemporal evolution of these volcanic fields is key for quantifying volcanic hazards and understanding magma genesis. The Black Rock Desert (BRD) volcanic field covers ∼700 km² of west-central Utah. We present 46 new ⁴⁰Ar/³⁹Ar ages from the BRD ranging from 3.7 Ma to 8 ka, which includes ⁴⁰Ar/³⁹Ar plateau ages from olivine separates. These new ages are combined with 13 recently published ⁴⁰Ar/³⁹Ar ages from the Mineral Mountains to evaluate the spatiotemporal evolution of all five BRD subfields. The oldest lavas and domes are located to the southwest, whereas the youngest lavas, which are only a few hundred years old, are located ∼30 km to the NNE. However, BRD vent migration patterns over the last 2.5 Ma are non-uniform. They are also not consistent with North American Plate motion over a partial melt zone nor have they migrated toward the center of the Colorado Plateau. BRD eruptions are almost always coincident with mapped Quaternary faults. A shear-velocity (Vs) model beneath the BRD indicates that the lithosphere has been thinned and that asthenospheric melt has coalesced at the lithosphere-asthenosphere boundary, which is supported by the trace element compositions of BRD lavas that signify that they have incorporated continental lithospheric mantle. Our data and observations suggest that the asthenosphere-lithosphere-volcanic system in the BRD is inherently complex.