HR: 0800h
AN: GP21A-0016    [Abstracts]
TI: Compilation of a Composite Geomagnetic Polarity Reversal Path Recorded in Basalts Erupted During Initial Yellowstone Hotspot Volcanism
AU: * Jarboe, N A
EM: njarboe@pmc.ucsc.edu
AF: University of California, University of California, Earth Sciences Department 1156 High St., Santa Cruz, CA 95064 United States
AU: Coe, R C
GP21A-0016 AF: University of California, University of California, Earth Sciences Department 1156 High St., Santa Cruz, CA 95064 United States
AU: Glen, J M
GP21A-0016 AF: US Geological Survey, MS989 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Renne, P R
GP21A-0016 AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AB: The Steens Basalts of the Columbia River Basalt Group erupted about 16-17 Ma covering southeastern Oregon, northern Nevada, and southwest Idaho with up to 600m of basaltic lavas. Later Basin and Range faulting created exposures containing up to 200 lava flows. At Steens Mountain these lavas were discovered to have recorded the most detailed volcanic record of a geomagnetic polarity reversal. Mankinen et al. (1985) and Camps et al. (1999) sampled two sections of these lavas in detail, known to be coeval by correlating a distinctive marker flow from one section to the other. Section A contains 51 flows erupted during the reversal while section B, 1.5 km away, contains 48 transitional flows. We have sampled two other sections that also contain transitional flows. At Catlow Peak 70 km to the SSE of Steens Mountain, 65 flows were sampled of which 32 were erupted during the transition. At Poker Jim Ridge 85 km to the west, 40 flows were sampled of which 36 were erupted during the transition. We presume these sections record the same reversal as at Steens and we will confirm contemporaneity with high precision 40Ar/39Ar ages. The agreement of transitional directions and their change through time are generally very good between sections, but significant additional detail is achieved by combining them. Samples from two transitional flows at Steens Mountain have been dated (16.69+-0.19 Ma and 16.48+-0.18 Ma), and dating of samples from Catlow Peak and Poker Jim Ridge are in progress. These four sections are combined into a more detailed composite record of the reverse-to-normal transition that we place at the bottom of the C5Cn.3n chron. The Steens basalt has recently been correlated with the R0-N0 transition of the CRBG on the basis of geologic mapping and geochemistry, although this interpretation has provoked some controversy. We are currently attempting to resolve this question by dating reversed and normal flows of the CRB Imnaha member.
DE: 1115 Radioisotope geochronology
DE: 1520 Magnetostratigraphy
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005