2004/12/13 by Stephen P. Reidel · 60 citations
Computer Science · Earth and Planetary Sciences · #Basalt #Effusive eruption #Flood basalt #Geochemistry #Geochemistry and Geologic Mapping #Geological and Geochemical Analysis #Geology #Geology and Paleoclimatology Research #Lava #Lava dome #Lava field #Paleontology #Petrology #Volcanism #Volcano
paper · doi:10.1086/425966
published in The Journal of Geology 113(1), 1-21 (University of Chicago Press)
openalex publication_date 2004/12/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22
The eruption of Sentinel Bluffs Member lava flows at approximately 15.5 Ma marked the end of Grande Ronde Basalt volcanism, the most voluminous period of the Columbia River Basalt Group. More than 10,000 km3 of lava erupted from northerly trending feeder dikes in eastern Washington and northern Oregon and flowed westward down an ancestral paleoslope covering more than 169,700 km2 of the flood‐basalt province. The Sentinel Bluffs Member consists of six phases or types defined by their compositions. Lava flows having the first compositional type were the most voluminous and reached the Pacific Ocean. The volume of later lava flows having the other compositional types declined with time until the final eruption produced the second‐largest volume of basalt. At the source area, compositional variation in Sentinel Bluffs lava flows is relatively small. This homogeneity allows the individual compositional types and, thus, phases of the eruption to be easily recognized. Farther west, however, compositional heterogeneity increases with several compositional types occurring in individual lava flows. The Cohassett flow has more compositional heterogeneity than any Sentinel Bluffs Member lava flow. It is interpreted to be a local lava flow that formed as one compositional type after another was injected into the first and inflated it to form a lava flow with compositional zoning reflecting the sequence of eruptions. The compositions of the layers remain intact except for mixing along their contacts. Thin vesicular horizons separate compositional layers in the upper part of the lava flow but not in the lower part. A thick vesicular horizon called the interior vesicular zone marks the boundary between the last two compositional types to be injected. Other Sentinel Bluffs flows appear to have formed in a similar way. The compositional types and the field relations are best explained by rapid changes in magma composition feeding and inflating the flows and suggest rapid eruption and emplacement of the lava flows.