Portland State University. Department of Earth Sciences
Marvin H. Beeson
Date of Award
Master of Science (M.S.) in Geology
1 online resource (162 p.)
Geology -- Oregon, Geochemistry -- Oregon
The North Fork stock is a composite intrusive body of Late Jurassic-Early Cretaceous age which outcrops in the Blue Mountains of northeastern Oregon. The upper 600 m of the intrusion are exposed over an area of approximately 36 km squared along the canyon walls of the North Fork of the John Day River in Grant and Umatilla counties. The stock intrudes metasediments, metavolcanics, and metagabbros associated with the Permian-Triassic Elkhorn Ridge Argillite. Contact metamorphism of the Elkhorn Ridge Argillite is developed to the hornblende-hornfels facies throughout most of the exposed area of this unit in the study area. The contact aureole of the North Fork stock extends away from the intrusive margins and ultimately grades into regionally metamorphosed greenschist- and amphibolite facies rocks. The metamorphic rocks exhibit a pronounced regional trend of foliation which is disrupted where it intersects intrusive contacts at steep angles.
Matty, David Joseph, "The geology and geochemistry of the North Fork stock, northeastern Oregon" (1979). Dissertations and Theses. Paper 3115.
Figure 5. Geologic Map of the North Fork Stock and Surrounding Area, northeastern Oregon
Figure 18 - Geologic Cross Sections A-A' and B-B' (1).pdf (556 kB)
Figure 18. Geologic Cross Sections A-A' and B-B'