SCARBERRY, Kaleb C., HUGHES, Scott S., and MCCURRY, Michael, Geosciences, Idaho State Univ, Pocatello, ID 83209,

The eastern Snake River Plain (ESRP) volcanic basin in southeast Idaho is underlain by ~1 km of dominantly olivine tholeiite basalt and interbedded sediment. This study refines subsurface stratigraphy of the F basalt flow group, a stratigraphically important sequence of uneroded, apparently comagmatic lava flows observed in drill core over an area of ~ 75 km2 between ~120-220 m depth. The ~565 ka F flow group erupted during an unusual, short-lived period of reversed magnetic polarity, probably in < 200 years. Detailed lithologic logs for six sections of F flows in drill-core reveal that the thickest (~50-60 m) lie in the southwest part of the study region, which we interpret to be near the vent. In each near-vent section 0.2-0.4 % higher P2O5 relative to values observed in the lower flow units characterize the uppermost lava flows. Chemical breaks are also identified in CaO/Al2O3 and K2O/TiO2 ratios. Preliminary trace element analyses indicate similar breaks at the same stratigraphic interval in incompatible elements. These chemostratigraphic characteristics support correlations between sampled sections. We interpret the F basalt flow group to have erupted from a source which sporadically tapped a periodically replenished magma chamber. Less evolved flows have slightly lower Sr-isotopic ratios than higher flows (0.7068 vs. 0.7071) while all exhibit similar Nd-isotope ratios (~0.5124). We infer that these isotopic signatures reflect magmatic derivation from an isotopically heterogeneous mantle source.

Cordilleran Section - 98th Annual Meeting (May 1315, 2002)
Session No. 30--Booth# 25
Pacific Northwest Geology East of the Cascades: In Honor of George W. Walker (Posters)
LaSells Stewart Center: Agriculture
1:30 PM-5:30 PM, Tuesday, May 14, 2002

© Copyright 2002 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.