Stratigraphy, structure, and petrology of Columbia River basalt in a portion of the Grande Ronde River--Blue Mountains area of Oregon and Washington

Technical Report · Thu Jun 01 04:00:00 EDT 1978

OSTI ID:6163258

Ross, M E

Lower, middle, and upper Yakima basalts are exposed in the canoyons of the Grande Ronde River and its tributaries in northeastern Oregon and southeastern Washington. The detailed stratigraphy of these Miocene to Pliocene basalts has been established in a portion of this area using a combination of flow and interbed mapping and correlations based on chemical, petrographic, and paleomagnetic properties of each flow. The lower Yakima flows have only a moderate range of compositions and form a chemical group most likely derived from a homogeneous magma source. All four of the lower Yakima magneto-stratigraphic units of Swanson and Wright are present, with N/sub 2/ confined mainly to the central, structurally lowest portion of the study area. Each of the middle and upper Yakima flows and flow pairs are chemically and petrographically distinct from one another. A detailed investigation of chemical variations across each of four middle and upper Yakima dikes shows that SiO/sub 2/, TiO/sub 2/, and K/sub 2/ decrease inward from chilled margins as MgO and perhaps CaO and total iron increase. P/sub 2/O/sub 5/ varies systematically only within the Wenaha dike, in which it decreases inward from the chilled dike margin. Petrgraphic and mineralogic variations across the dikes were studied in detail. The presence of broad folds; strike-slip faults showing a second, lesser dip-slip movement; a monocline; and normal faults indicates the area was subjected to a nearly north--south compression followed by relaxation and tensional tectonic forces.

• Research Organization: Atomics International Div., Richland, WA (USA). Rockwell Hanford Operations
• DOE Contract Number: EY-77-C-06-1030
• OSTI ID: 6163258
• Report Number(s): RHO-SA-58
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
BASALT
CHEMICAL COMPOSITION
COLUMBIA RIVER
DEFORMATION
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
MINERALOGY
NORTH AMERICA
OREGON
PACIFIC NORTHWEST REGION
PETROLOGY
RIVERS
ROCKS
STRATIGRAPHY
STREAMS
SURFACE WATERS
TECTONICS
USA
VOLCANISM
WASHINGTON