Structural and Volcanic Evolution of the Glass Buttes Area, Oregon

Abstract

The Glass Buttes volcanic complex is a cluster of bimodal, Miocene to Pleistocene age lava flows and domes located in Oregon’s High Lava Plains province. The area is cut by NW striking faults of the Brothers Fault Zone (BFZ), a ~300 km long, N60°W trending zone of en echelon faults. Individual fault segments are 10-20 km long, striking~N40°W and display apparent normal separation. A smaller population of ~5km long faults strike ~N30°E (Lawrence, 1976). Current regional kinematic models for BFZ deformation (Lawrence, 1976, Trench, 2008) necessitate a significant component of dextral strike-slip motion across BFZ faults. The faults at Glass Buttes show evidence of low to moderate amounts of vertical separation (<60m throw). Lack of observable strike-slip separation, along with common horst and graben topography and measured kinematic indicators suggest predominantly normal to slightly oblique displacement along BFZ faults at Glass Buttes. The current study combines LiDAR based geologic mapping, GIS analysis, detailed gravity modeling and new 40Ar / 39Ar age data to constrain the timing, rate and style of deformation in the Glass Buttes area. Current regional tectonic models for the BFZ will be evaluated and updated in light of these findings; and structural interpretations will support targeting of geothermal exploration wells.