HR: 0830h
AN: V31E-0980    [PDF]
TI: Chemical Stratigraphy of the Weiser Embayment Columbia River Basalt
AU: * Harrison, B K
EM: bkimballh@hotmail.com
AF: Carleton College, Department of Geology 1 N College St, Northfield, MN 55057
AU: Haileab, B
EM: bhaileab@carleton.edu
AF: Carleton College, Department of Geology 1 N College St, Northfield, MN 55057
AB: We present a detailed examination of the surficially exposed flows of the Imnaha and Grande Ronde subunits of the Columbia River Basalt (CRB) in the vicinity of McCall, Idaho. These samples represent the northern margin of CRB outcropping in the Weiser Embayment, and belong among the easternmost of CRB extrusions. Major and trace element data are presented along with petrographic analysis with comparison to the Imnaha and Grande Ronde Basalt type sections. Exposed Imnaha Basalt flows in the region appear to be mostly restricted to later erupted members of the American Bar chemical type with isolated flows of the Rock Creek type. The Grande Ronde Basalt of the region is relatively thin, and is predominantly composed of the N1 magnetostratigraphic unit. This study includes over 100 new whole rock major and trace element analyses by XRF and ICP-MS. Preliminary results suggest that a flow-by-flow chemical correlation is possible with the Imnaha and Grande Ronde type sections. Samples of the American Bar chemical type appear to be moderately more primitive than equivalent flows in the vicinity of the Imnaha River. This may warrant further investigation into the overall composition of the Imnaha Basalt.
DE: 3625 Descriptive mineralogy
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting