An integrated geophysical imaging of the upper-crustal features in the Harney Basin, southeast Oregon

Abstract

The Harney Basin is a relatively fl at-lying depression in the northeast corner of the enigmatic High Lava Plains volcanic province in eastern Oregon. A thick blanket of volcanics including fl ood basalts, rhyolites, tuffs, ash fl ows, and distinct eruptive centers covers the basin, making it very diffi cult to study the upper-crustal features. In addition to a portion of the High Lava Plains active source seismic data in the Harney Basin area, we employed geologic, gravity, magnetic, digital elevation, and other geospatial data in our integrated study. We generated an upper-crustal 3D seismic tomographic model of the Harney Basin using a sparse grid of 2D seismic lines and constructed an integrated geophysical model of the upper-crustal structure, which reveals that the basin reaches as deep as 6 km in its central area. The tomographic inversion also detected some unusually high-velocity (>6.5 km/s) bodies in the upper crust near the central basin area. The presence of several ash-fl ow tuffs and voluminous rhyolites in the Harney Basin region indicates that the sources of these materials are nearby. We observe two major calderashaped features within the basin, which we interpret to be likely candidates for the source of some of these tuffs. These potential calderas are associated with low seismic velocities, low gravity anomaly values, and topographic depressions. We interpret the extent and evolution of these potential calderas based on our integrated analysis.