Portland State University. Department of Geology
Michael L. Cummings
Date of Award
Master of Science (M.S.) in Geology
1 online resource (140 p.)
Geology -- Oregon -- Bear Creek Butte Region, Hydrothermal deposits -- Oregon -- Bear Creek Butte Region, Mineralogy -- Oregon -- Bear Creek Butte Region
The Eocene Clarno Formation, the Oligocene John Day Formation and basalts of the High Lava Plains are exposed in the Bear Creek Butte area in Central Oregon. In this area the Clarno Formation can be divided into a lower sequence composed of intermediate lava flows with intercalated mudflows and volcaniclastic sediments and an upper sequence of rhyolite and basalt flows and felsic ruffs. Separating the two units is a well developed saprolite. The change from intermediate to rhyolite-basalt volcanism reflects a change in the tectonic environment of the Cascade volcanic arc from compression to relaxation as subduction of the Farallon plate by the North American plate slowed, allowing extension of the continental plate margin to occur.
Wilkening, Richard Matthew, "The geology and hydrothermal alteration of the Bear Creek Butte area, Crook County, central Oregon" (1986). Dissertations and Theses. Paper 3656.