Late Jurassic magmatism, metamorphism, and deformation in the Blue Mountains Province, northeast Oregon

Joshua J. Schwartz, Arthur W. Snoke, Fabrice Cordey, Kenneth Johnson, Carol D. Frost, Calvin G. Barnes, Todd A. LaMaskin, Joseph L. Wooden

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


An early to mid-Mesozoic record of sedimentation, magmatism, and metamorphism is well developed in the Blue Mountains Province of northeast Oregon. Detailed studiesboth north and south of the Blue Mountains Province (e.g., terranes of the Intermontane belt, Klamath Mountains, and western SierraNevada) have documented a complex Middle to Late Jurassic orogenic evolution. However, the timing of magmatic, metamorphic, and deformational events in the Blue Mountains, and the significance of these events in relationship to other terranes in the western North American Cordillera remainpoorly understood. In this study, we investigate the structural, magmatic, and metamorphic histories of brittle to semibrittle deformation zones that indicate widespread Late Jurassic orogenesis in the Blue Mountains Province. Folding and faulting associated with contractional deformation are primarily localized along terrane boundaries (e.g., Baker-Wallowa and Baker-Izee-Olds Ferry boundaries) and within the composite Baker oceanic mélange terrane (e.g., Bourne-Greenhorn subterrane boundary). These brittle to semibrittle deformation zones are broadly characterized by the development of E-W-oriented slaty to spaced cleavage in fine-grained metasedimentary rocks of the Baker terrane (e.g., Elkhorn Ridge Argillite), approximately N-S-bivergent folding, and N-and S-dipping reverse and thrust faulting on opposite flanks of the Baker terrane. Similarly oriented contractional features are also present in late Middle Triassic to early Late Jurassic (i.e., Oxfordian Stage, ca. 159 Ma) sedimentary rocks of the John Day and Huntington areas of northeast Oregon. Radiometric age constraints from youngest detrital zircons in deformed sedimentary rocks and crystallization ages of postkinematic plutons, which intrude the deformation zones, limit deformation to between ca. 159 and ca. 154 Ma. We suggest that the widespread, approximately N-S-directed contractional features in the Blue Mountains Province record a short-lived, intense early Late Jurassic deformational event and preserve an example of upper-crustal strain localization associated with terminal arc-arc collision between the Olds Ferry and Wallowa island-arc terranes. The age interval of deformation in the Blue Mountains Province is younger than Middle Jurassic deformation in the CanadianCordillera and Klamath Mountains (Siskiyou orogeny) and predates classic Nevadan orogenesis.

Original languageEnglish
Pages (from-to)2083-2111
Number of pages29
JournalBulletin of the Geological Society of America
Issue number9-10
StatePublished - Sep 2011


Dive into the research topics of 'Late Jurassic magmatism, metamorphism, and deformation in the Blue Mountains Province, northeast Oregon'. Together they form a unique fingerprint.

Cite this