Rocky Mountain (63rd Annual) and Cordilleran (107th Annual) Joint Meeting (1820 May 2011)
Paper No. 3-5
Presentation Time: 9:25 AM-9:45 AM


STRECK, Martin J.1, FERNS, Mark L.2, RICKER, Christopher1, and STEINER, Arron1, (1) Department of Geology, Portland State University, Portland, OR 97207,, (2) Science Department, Eastern Oregon University, La Grande, OR 97850

A not often appreciated part of Columbia River Basalt Group (CRBG) volcanism is the closely associated silicic volcanism. Large rhyolite vent complexes form a belt that stretches over 300 km from near Baker City, Oregon to northern Nevada. Voluminous silicic eruptions from these centers span the time frame between 16.5 to 15 Ma, coincident with the most voluminous CRBG flood basalts. Here, we focus on silicic volcanism in the northern 100 km segment, which overlaps the proposed location of CRBG crustal magma reservoirs (Wolff et al., Nature Geoscience, 2008). Our current data indicate silicic volcanism here began at 16.4 Ma. Initial calc-alkaline compositions become more Fe-rich and A-type like with time. One of the major northern rhyolite centers generated the voluminous Dinner Creek Ash-flow Tuff. Although the vent complex is yet to be mapped in detail, the source of the Dinner Creek Tuff lies between Castle Rock and Iron Mtn. An exposure of more than 70 m thick rheomorphic Dinner Creek Tuff at Iron Mtn. defines the northern near-vent facies. Several hundred thousand years of silicic volcanism produced multiple fall and ash-flow deposits at this complex. Duration of activity is currently defined by new Ar-Ar dates ranging from 15.9±0.13 to 15.4±0.16 (2σ) Ma on feldspar separates from Dinner Creek Tuff ignimbrites. Some younger tuffs with subtle chemical differences have nearly identical ages ranging between 15.45±0.16 and 15.38±0.17 (2σ) Ma. Welded tuff lithics with Dinner Creek Tuff compositions indicate recycling of older tuffs and provide further evidence for multiple ignimbrite eruptions. Ash-flow tuffs that erupted from the Dinner Creek Tuff center extend over an area of more than 20,000 km2 and, through our new correlations, include the Mascall Ignimbrite of the greater Paulina Basin and the Pleasant Valley Tuff of the Baker valley. Other correlative ash-flow tuffs extend from the Silvies River north of Burns, to John Day, Prairie City, and Unity, and as far north as La Grande suggesting an eruption volume of several 100’s of km3 which is also suggested by Dinner Creek Tuff fallout extending from northern Nevada (Nash et al., EPSL, 2008) to Umatilla county, Oregon.

Rocky Mountain (63rd Annual) and Cordilleran (107th Annual) Joint Meeting (1820 May 2011)
General Information for this Meeting
Session No. 3
Petrologic and Geodynamic Perspectives on Non-Arc Volcanism in the Western United States
Riverwoods Conference Center: Juniper
8:00 AM-12:00 PM, Wednesday, 18 May 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 4, p. 5

© Copyright 2011 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.