2009 Portland GSA Annual Meeting (18-21 October 2009)
411 Thursday, 15 October 2009
12:00 PM-6:00 PM, Boise Airport:

A Tectonic Transect Through the Salmon River Suture Zone Along the Salmon River Canyon in the Riggins Region of West-Central Idaho

Primary Leader: David E. Blake
Leader(s): Scott Giorgis, Basil Tikoff, Keith Gray
Field Trip Description: This three-day field trip focuses on a west to east cross section through west-central Idaho from the Seven Devils Mountains into the Salmon River Canyon. Billed as the second deepest gorge in North America, the Salmon River Canyon offers spectacular cross-strike exposures through mid-crustal levels of the Salmon River suture zone (SRSZ) and western Idaho shear zone (WISZ) in the Riggins region. Together, these structures record mid-Mesozoic to Cenozoic accretion of the Blue Mountains island arc with the ancestral western Laurentian margin, transpression in the WISZ, and Basin and Range-style extension. All of these tectonic features are localized along a subvertically oriented, lithospheric-scale, arc-continent boundary. We will view (1) different lithotectonic domains across the SRSZ, including Wallowa terrane arc volcanogenic and Norian carbonate rocks, back-arc basin metasedimentary and metavolcanic rocks of the Riggins Group and Pollock Mountain amphibolite, deformed plutonic rocks in the WISZ, and Precambrian metasedimentary rocks of Laurentia; (2) polyphase fold-thrust belt deformation across a greenschist-amphibolite facies metamorphic gradient and the interplay between dextral transpression and partial melting of syn- to post-tectonic granitoid plutons; and (3) ductile-brittle extensional overprint of pre-existing rocks and structures, including late Cenozoic Columbia River basalt flows. Quaternary mass wasting and terracing are prevalent along the river. The field trip honors the 40th publication anniversary of the reconnaissance geologic map of the Riggins quadrangle by Warren Hamilton. The field trip begins in Boise, ends in Portland, and includes a regional overview of the SRSZ and WISZ while traveling.
Field Trip will span: 3 days
Sponsor(s): GSA Sedimentary Geology Division

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