Descriptive summary of the Grande Ronde Basalt type section, Columbia River Basalt Group

Technical Report · Sun Oct 01 04:00:00 EDT 1978

DOI:https://doi.org/10.2172/6162969· OSTI ID:6162969

Camp, V. E.; Price, S. M.; Reidel, S. P.

The Grande Ronde Basalt type section, located in extreme southeastern Washington, was measured, sampled, and characterized. The section is 800 meters thick and is comprised of 35 Grande Ronde Basalt flows. These flows are divisible into 3 magnetostratiographic units termed, in ascending order, the R/sub 1/, the N/sub 1/, and the R/sub 2/. The R/sub 1/ unit is represented by 13 reversely polarized flows; the N/sub 1/ unit, by 13 normally polarized flows; and the R/sub 2/, by 9 reversely polarized flows. Chemically, the Grande Ronde Basalt flows are divided into 2 major groups, termed A and B. The compositions of the lower 9 flows, members of Group A, are similar to either the high-Mg Grande Ronde chemical type, the high-Ti Grande Ronde chemical type, or the Pomona chemical type. The compositions of the upper 25 flows, members of Group B, are predominantly similar to the low-Mg Grande Ronde chemical type. Petrographically, the Grande Ronde Basalt flows are generally fine grained and aphyric, and have a intergranular or intersertal micro-texture. Major mineral phases include plagioclase (An/sub 40-60/) and augite; minor mineral phases include pigeonite, orthopyroxene, ilmenite, titanomagnetite, and olivine. Group A flows generally contain more olivine and less pigeonite than do Group B flows. 6 figures, 6 tables.

• Research Organization: Atomics International Div., Richland, WA (USA). Rockwell Hanford Operations
• DOE Contract Number: EY-77-C-06-1030
• OSTI ID: 6162969
• Report Number(s): RHO-BWI-LD-15
• Country of Publication: United States
• Language: English

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