Blue Mountains Field Trip: March 24-29, 2007

Columbia River Basalts rest on Mesozoic accreted terrane rocks high above the Snake River, western Idaho. Here we are in late July, 2006, shortly before our brains melted in the extreme heat of the day. Reed Lewis, Todd LaMaskin, Jeff Vervoort, and Keegan Schmidt (photo by Becky Dorsey).

Contacts:

Becky Dorsey (rdorsey@uoregon.edu)

Todd LaMaskin (tlamaski@uoregon.edu)

Tracy Vallier (tlvallier@hotmail.com)

This trip brings together a diverse group of graduate and undergraduate students, faculty, and other professionals from four universities and the Idaho and Oregon state geological surveys. The UO contingent will depart Eugene the morning of March 24, camp that night in central Oregon at Clyde Holliday Park, and make our way to Oxbow on the Snake River by mid-day Sunday March 25. On March 26 and 27 we will take jetboats down the river to view Mesozoic plutonic, volcanic and sedimentary rocks, as well as intensely deformed metamorphic shear zones and mylonites. March 28 we will drive through western Idaho to view metamorphic rocks in the Salmon River Belt and Western Idaho Shear Zone, and we'll stay at the Idaho Field Station in McCall that night. Thursday the 29th we will drive all the way back to Eugene, and collapse.

PREPARATION FOR THE TRIP

We are having a series of informal weekly meetings to help prepare for the field trip. Informaton and papers posted below are provided for people who will attend the field trip, and anyone else interested in these topics.

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Have a look at this working Time Line (or get the pdf version) for the tectonic/geologic evolution of the Pacific Northwest region. This compilation contains lots of controversial ideas and models that we will discuss during the next month and beyond ...

Here is a working map compilation of NE Oregon and Western Idaho (or get the pdf version)

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READINGS - this is a tentative, evolving schedule:

(1) March 1: Overview of Cordilleran Tectonics

Pick up a copy of today's presentation: Summary of Cordilleran Tectonics.

Dickinson (2004) - Evolution of the Western Cordillera of North America. Annual Review of Earth and Planetary Sciences, v. 32, p. 13-45.

Dickinson (2006) - Geotectonic Evolution of the Great Basin. Geosphere, v. 2, p. 353–368.

The above two papers provide a useful broad overview of the Cordilleran system, and they help us set the stage for thinking about the history of terrane accretion and related crustal processes in Oregon and western Idaho. If your time is limited, you might try focusing on this region. However, since the relevance of the regional geology is best appreciated by placing it in a bigger tectonic context, I suggest we begin with an orogen-scale overview of the western Cordillera. By the end of this meeting we should be able to steer the focus into the PNW region and set ourselves up for the following week.

(2) March 8: Mesozoic Tectonics of Oregon and Western Idaho

Here is a pdf copy of today's presentation: Overview of Blue Mts Tectonics.

Vallier (1995) - Petrology of pre-Tertiary igneous rocks in the Blue Mountains region of Oregon, Idaho, and Washington; implications for the geologic evolution of a complex island arc, in Vallier, T.L., and Brooks, H.C. (eds.), Geology of the Blue Mountains region of Oregon, Idaho, and Washington: petrology and tectonic evolution of pre-Tertiary rocks of the Blue Mountains region: USGS Professional Paper 1438, p. 125-209.

Dorsey and LaMaskin (in review) - Basinal response to Triassic-Jurassic collisional tectonics in the Blue Mountains Province, northeastern Oregon. Submitted to American Journal of Science.

(3) March 15: Tectonic evolution of western Idaho, a quick overview

Here is a pdf copy of today's presentation: Overview of Western Idaho Tectonics.

Giorgis et al (2005) - Missing Idaho arc: Transpressional modification of the 87Sr/86Sr transition on the western edge of the Idaho batholith: Geology, v. 33, p. 469-472.

Gray and Oldow (2005) - Contrasting structural histories of the Salmon River belt and Wallowa terrane: Implications for terrane accretion in northeastern Oregon and west-central Idaho: Geological Society of America Bulletin, v. 117, p. 687-706. A recent study of western Idaho, with new insights into Jurassic deformation and mountain building that directly relate to formation and growth of the collisional Izee basin.

McClelland et al (2000) - Two-phase evolution of accretionary margins: examples from the North American Cordillera: Tectonophysics, v. 326, p. 37-55.

(4) March 22: Mop-Up, Discussion, Logistics

Stay tuned for details ...

RELATED LINKS:

Mesozoic Tectonics of the Blue Mts - summary of Becky's and Todd's ongoing research here.

Accreted Terranes in western Idaho - provided by ISU in collaboration with the Idaho Geological Survey

Overview of concepts in Cordilleran Tectonics ... from a National Parks course taught by Michael Stewart at UIUC.

Gene's summary of Columbia River Basalts, uplift of the Wallow Mountains, and the delamination hypothesis.

Vic Camp's web page - link from there to How Volcanoes Work, and Radiating Volcanic Migrations

NAVDAT - the Western North America Volcanic and Intrusive Rock Data Base. Link to Animations.

Alan Glazner's homepage - scroll down or link to What's New

Ron Blakey's paleogeographic reconstructions of the western U.S. through geologic time.

ADDITIONAL READING (a fairly random selection):

Avé Lallemant, H.G., Schmidt, W.J., and Kraft, J.L., 1985, Major Late-Triassic strike-slip displacement in the Seven Devils Terrane, Oregon and Idaho: a result of left-oblique plate convergence: Tectonophysics, v. 119, p. 299-328.

Camp and Ross (2004) - JGR paper with data and concepts that support a modified plume model for Columbia River Basalts (CRB) eruptions.

Cowan and Reiners (2004) Age and provenance of lower Tertiary fluvial strata, Elkhorn Mountains, E. Oregon. Geological Society of America Abstracts with Programs, Vol. 36, No. 4, p. 34.

Brooks, H.C., and Vallier, T.L., 1978, Mesozoic rocks and tectonic evolution of eastern Oregon and western Idaho, in Howell, D.G., and McDougall, K.A., ed., Mesozoic paleogeography of the western United States: Society of Economic Paleontologists and Mineralogists, Pacific Section, Paleogeography Symposium 2, p. 133-145.

Dickinson, W.R., 1979, Mesozoic forearc basin in central Oregon: Geology, v. 7, no. 4, p. 166-170.

Dickinson, W.R., and Thayer, T.P., 1978, Paleogeographic and paleotectonic implications of Mesozoic stratigraphy and structure in the John Day inlier of central Oregon, in Howell, D.G., and McDougall, K.A., eds., Mesozoic paleogeography of the western United States: Society of Economic Paleontologists and Mineralogists, Pacific Section, Paleogeography Symposium 2, p. 147-161.

Follo, M.F., 1992, Conglomerates as clues to the sedimentary and tectonic evolution of a suspect terrane: Wallowa Mountains, Oregon: Geological Society of America Bulletin, v. 104, p. 1561-1576.

Hales et al. (2005) - Nature paper presents a model for delamination (sinking) of the dense root of the Wallowa Batholith and related upper-mantle convection, eruption of the CRBs, and buoyancy-driven uplift of the Wallowa Mountains.

Housen, B. A. and Dorsey, R.J. (2005) Paleomagnetism and tectonic significance of Albian and Cenomanian turbidites, Ochoco basin, Mitchell Inlier, central Oregon. Journal of Geophysical Research vol. 110, B07102, doi:10.1029/2004JB003458.

Humphreys et al. (2000) - GSA Today paper presents geophysical evidence for local upper-mantle convection as the underlying mechanism that drives the Yellowstone and Newberry hotspots.

Kays, M.A., Stimac, J.P., and Goebel, P., 2006, Permian-Jurassic growth and amalgamation of the Wallowa composite terrane, northeastern Oregon, n Geologic Society of America Special Paper 410, eds. A.W. Snoke and C.G. Barnes, (volume in honor of William P. Irwin), p. 465-494.

Manduca, C.A., Kuntz, M.A., and Silver, L.T., 1993, Emplacement and deformation history of the western margin of the Idaho Batholith near McCall, Idaho; influence of a major terrane boundary: Geological Society of America Bulletin, v. 105, p. 749-765.

Manduca, C.A., Silver, L.T., and Taylor, H.P., 1992, 87Sr/86Sr and 18O/16O isotopic systematics and geochemistry of granitoid plutons across a steeply-dipping boundary between contrasting lithospheric blocks in western Idaho: Contributions to Mineralogy and Petrology, v. 109, p. 355-372.

Pessagno, E.A., 2006, Faunal evidence for the tectonic transport of Jurassic terranes in Oregon, California and Mexico, in Geologic Society of America Special Paper 410, eds. A.W. Snoke and C.G. Barnes, (volume in honor of William P. Irwin), p. 31-52.

Selverstone, J., Wernicke, B.P., and Aliberti, E.A., 1992, Intracontinental subduction and hinged unroofing along the Salmon River suture zone, west central Idaho: Tectonics, v. 11, p. 124-144.

Tikoff et al. (2001) "Lithospheric and crustal reactivation of an ancient plate boundary: the assembly and disassembly of the Salmon River suture zone, Idaho, USA". In: Holdsworth et al (eds.) Geol. Soc. London Spec. Pub. 186.

Vallier (1998) Islands and Rapids, A geologic story of Hells Canyon, Confluence Press, 151 pp.

Wyld and Wright (2001) , Wyld (2002) , Wyld (1996) , Wyld et al. (1996) , Wyld (2000) , Wyld et al (2003) , Wyld et al. (in press) - An impressive series of papers by Sandra Wyld and colleagues that deal with Mesozoic magmatism, deformation, mountain building, metamorphism, and regional tectonic reconstructions for Nevada and the Pacific Northwest region.

ITINERARY:

Saturday March 24: Drive to Mount Vernon, do geology south of John Day, and camp at Clyde Holliday campground. We will meet at the Canyon City Post Office at 2:00 p.m. Saturday and do geology south of there for the rest of the afternoon.

Sunday March 25: Drive through Baker City, do roadside geology, and get to Oxbow around mid-day. Meet everyone at Copperfield Campground and form a big group (about 30). Starting at about 2:00 we will view exposures in theOxbow area, to help prepare for the next two days.

Monday 26th: Jetboat down the river to see Permian and Triassic volcanic rocks, Kirkwood and Cougar Creek Complex, etc. Camp at Copperfield campground.

Tuesday 27th: Jetboat down the river to see Triassic volcanics and overlying sedimentary rocks at Pittsburgh Landing, etc. Camp at Copperfield campground.

Wednesday 28th: Drive into western Idaho, do roadstops in the Salmon River belt and Western Idaho shear zone, end day at the Idaho Field Station and stay there.

Thursday 29th: Drive back to Eugene.

People are more than welcome to join us for any/all parts of this trip. I will be happy to provide more details of what to expect on the river, though we are still in the process of refining that plan. Stay tuned for more info.