CRUSTAL STRUCTURE IN THE HIGH LAVA PLAINS REGION FROM INTEGRATED GEOPHYSICAL STUDIES

The High Lava Plains (HLP) of eastern Oregon, the Columbia Plateau (CP), and the Snake River Plain (SRP) share many geologic characteristics in terms of the timing and petrologic nature of the massive magmatism in the last 16Ma. However, many intriguing questions about their origin and evolution remain, and the origin of the crust in several areas is poorly known. The HLP have recently been the target of a large research effort that featured both controlled-source and natural-source seismic experiments and well as a variety of geological and petrological investigations. The initial results of these efforts when integrated with EarthScope and other data in the region are producing a new understanding of the crustal structure and evolution of this complex area. The HLP appears to have only experienced modest magmatic modification of the middle and lower crust. However, the effects of crustal thinning due Basin and Range extension are clear in the south. The crust of the Columbia Plateau (CP) is thicker and more mafic than in the HLP region. The eastern and western portions of the Snake River Plain have different geologic characteristics but very similar geophysical signatures that are much more prominent that those of the HLP and CP. These signatures indicate major magmatic modification of the preexisting crust. As would be expected the crust of the Cascade Range is thicker that in any of these areas. Our new models of crustal structure are being integrated into a regional framework that produces an improved understanding of the structure and evolution of the lithosphere of this complex and intriguing region.