Introduction: Hells Canyon to the Bitterroot front: A transect from the accretionary margin eastward across the Idaho batholith

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Authors
Lewis, Reed S.
Schmidt, Keegan L.
Gaschnig, Richard M.
LaMaskin, Todd A.
Lund, Karen
Gray, Keith D.
Tikoff, Basil
Stetson-Lee, Tor
Moore, Nicholas
Advisors
Issue Date
2014
Type
Article
Keywords
North-American cordillera , Blue mountains province , U-PB geochronology , West-central Idaho , Metamorphic core complex , Cougar creek complex , Belt-Purcell basin , River suture zone , Northeastern Oregon , Wallowa terrane
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Citation
Lewis, Reed S.; Schmidt, Keegan L.; Gaschnig, Richard M.; LaMaskin, Todd A.; Lund, Karen; Gray, Keith D.; Tikoff, Basil; Stetson-Lee, Tor; Moore, Nicholas. 2014. Introduction: Hells Canyon to the Bitterroot front: A transect from the accretionary margin eastward across the Idaho batholith, In: Exploring the Northern Rocky Mountains, GSA Field Guides, vol. 37, 2014: pp 1-50
Abstract

This field guide covers geology across north-central Idaho from the Snake River in the west across the Bitterroot Mountains to the east to near Missoula, Montana. The regional geology includes a much-modified Mesozoic accretionary boundary along the western side of Idaho across which allochthonous Permian to Cretaceous arc complexes of the Blue Mountains province to the west are juxtaposed against autochthonous Mesoproterozoic and Neoproterozoic North American metasedimentary assemblages intruded by Cretaceous and Paleogene plutons to the east. The accretionary boundary turns sharply near Orofino, Idaho, from north-trending in the south to west-trending, forming the Syringa embayment, then disappears westward under Miocene cover rocks of the Columbia River Basalt Group. The Coolwater culmination east of the Syringa embayment exposes allochthonous rocks well east of an ideal steep suture. North and east of it is the Bitterroot lobe of the Idaho batholith, which intruded Precambrian continental crust in the Cretaceous and Paleocene to form one of the classical North American Cordilleran batholiths. Eocene Challis plutons, products of the Tertiary western U.S. ignimbrite flare-up, intrude those batholith rocks. This guide describes the geology in three separate road logs: (1) The Wallowa terrane of the Blue Mountains province from White Bird, Idaho, west into Hells Canyon and faults that complicate the story; (2) the Mesozoic accretionary boundary from White Bird to the South Fork Clearwater River east of Grangeville and then north to Kooskia, Idaho; and (3) the bend in the accretionary boundary, the Coolwater culmination, and the Bitterroot lobe of the Idaho batholith along Highway 12 east from near Lewiston, Idaho, to Lolo, Montana.

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Publisher
Geological Society of America
Journal
Book Title
Series
Exploring the Northern Rocky Mountains, GSA Field Guides;v.37
PubMed ID
DOI
ISSN
2333-0937
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