2009 Portland GSA Annual Meeting (18-21 October 2009)
429 Wednesday, 21 October 2009
1:00 PM-6:00 PM, Oregon Convention Center:

Mesozoic Sedimentation, Magmatism, and Tectonics in the Blue Mountains Province, Central Oregon

Primary Leader: Todd LaMaskin
Leader(s): Johnson Ken, Art Snoke, Schwartz Joshua
Field Trip Description: This trip will examine Upper Triassic to Jurassic sedimentary rocks of the Izee terrane and associated Paleozoic basement and Jurassic magmatic rocks in the adjacent Baker terrane. This will provide an opportunity for wide-ranging discussions of Mesozoic sedimentation, magmatism, and tectonics of the western U.S. and Canadian Cordillera. We will depart Portland at 1 pm on Wednesday, October 21, and drive ~ 6 hrs to John Day, Oregon. On Thursday, October 22, we will visit basement exposures of serpentinite-matrix mélange and overlying Triassic sedimentary strata. We will traverse up-section through Triassic and Jurassic rocks that include olistostromal slide blocks and volcaniclastic turbidites. We will examine new detrital-zircon data that have implications for the tectonic evolution of the region and possible links to the Klamath Mountains and southern British Columbia. On Friday, October 23, we will visit Late Jurassic plutons and associated volcanic rocks exposed in the Baker terrane east of John Day. We will examine two compositionally and geochemically distinct plutons that record magmatism at 157 and 146 Ma, and examine host rocks including basaltic andesite flows and volcaniclastic breccias. Discussion will focus on petrographic and geochemical characteristics of the Late Jurassic igneous rocks, their petrogenesis, and their relationship to orogenic events in the Blue Mountains. We will also examine Mesozoic volcanogenic sedimentary rocks in the Dixie Butte complex, and compare them to sedimentary rocks observed on day one. We will depart John Day at ~ 8 am on Saturday, October 24, and return to Portland ~ 2 pm.
Field Trip will span: 4 days
Sponsor(s): GSA Sedimentary Geology Division

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