Stratigraphy and petrogenesis of the Grande Ronde basalt in the lower Salmon and adjacent Snake River canyons
Technical Report
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OSTI ID:6184105
The Imnaha basalt, the Grande Ronde basalt, and the Saddle Mountains basalt were mapped in a 1000-km/sup 2/ area encompassing the lower Salmon and adjacent Snake River canyons. Stratigraphic data were collected from 17 Grande Ronde basalt sections and 7 Imnaha basalt sections. Four hundred fourteen Grande Ronde and Imnaha basalt samples were analyzed using XRF procedures. One hundred Grande Ronde basalt samples were analyzed for trace elements using INAA procedures. The Grand Ronde basalt samples were separated into flows and flow groups by use of field characteristics, stratigraphic position, and chemical composition. The spatial distribution of the flows and flow groups suggests the flows were supplied from two known source areas. The primary source was the Chief Joseph dike swarm west of the area and of lesser importance was the Rocky Canyon source to the east. Petrologic studies show that orthopyroxene, plagioclase, and olivine crystallized at relatively shallow depths. At still shallower depths, orthopyroxene was resorbed by the liquid and pigeonite began to crystallize. Augite, plagioclase, and olivine crystallized after eruption with accessory amounts of pigeonite, ilmenite, magnetite, and apatite. The paragenetic sequence indicates several storage stages for the liquids before eruption. Variations in the flow compositions follow stratigraphic relationships and result primarily from the contribution of clinopyroxene to the liquid. Plagioclase was more important in producing compositional variations in the older, less siliceous Grande Ronde basalt flows. Many oxide pairs for the flows and flow groups have linear relationships that can only be explained using multicomponent mineral systems. Least-Squares modeling indicates the mineral phases necessary to produce the observed relationships. It is suggested that a combination of partial melting and low pressure-fractionation produced the observed chemical variations. 89 references, 81 figures, 46 tables.
- Research Organization:
- Rockwell International Corp., Richland, WA (USA). Rockwell Hanford Operations
- DOE Contract Number:
- EY-77-C-06-1030
- OSTI ID:
- 6184105
- Report Number(s):
- RHO-SA-62
- Country of Publication:
- United States
- Language:
- English
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Mon Dec 31 23:00:00 EST 1984
· Geol. Soc. Am., Abstr. Programs; (United States)
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OSTI ID:6898740