Crustal structure of the Ruby Mountains metamorphic core complex, Nevada, from passive seismic imaging

Abstract

We use data from a temporary passive seismic array to illuminate the deep structure of the Ruby Mountains metamorphic core complex (RMCC). Despite decades of geologic mapping and geophysical exploration, the relative importance of lateral crustal flow, diapirism, and brittle faulting in the formation of the RMCC has remained unclear. Our Ruby Mountains Seismic Experiment (RMSE) utilized 50 passive broadband stations from 2010 to 2012 spaced at 5-10 km along three ~100-km-long intersecting profiles as part of the Earthscope Flexible Array program. Common conversion point stacks of our P-wave receiver functions show a fairly flat Moho at 32 ± 2 km depth throughout most of the study area but reaching 40 km in a narrow, north-south crustal welt 20-50 km west of the exposed RMCC. Our shear-wave splitting analysis shows that fast directions of polarization rotate clockwise from west to east across our study area, broadly matching regional studies and models that placed the anisotropy below the lithosphere. However, because our north-south crustal welt coincides with W-E polarizations, the observed splitting may include a component of crustal anisotropy. We integrate our observations with older magnetotelluric and seismic refraction and reflection data to support a model of asymmetric crustal flow during formation of the RMCC at the edge of a preexisting orogenic plateau.