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A rift-edge facies of the Late Jurassic Rogue–Chetco arc and Josephine ophiolite, Klamath Mountains, Oregon

Yule, J. Douglas and Saleeby, Jason and Barnes, Calvin G. (2006) A rift-edge facies of the Late Jurassic Rogue–Chetco arc and Josephine ophiolite, Klamath Mountains, Oregon. In: Geological studies in the Klamath Mountains province, California and Oregon: a volume in honor of William P. Irwin. Special papers (Geological Society of America). No.410. Geological Society of America , Boulder, CO, pp. 53-76. ISBN 9780813724102.

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The western Jurassic belt of the Klamath Mountains represents one of the Earth's best-preserved exposures of ancient marginal ocean basin lithosphere and chiefly consists of the coeval Rogue–Chetco volcanic-plutonic oceanic arc and Josephine ophiolite. This Late Jurassic ocean basin is hypothesized to have formed in response to rifting that initiated at ca. 165 Ma along the western margin of North America, disrupting a Middle Jurassic arc that had been constructed on older Klamath terranes and forming a marginal ocean basin with an active arc, inter-arc basin, and remnant arc. Previous workers characterized a “rift-edge” facies in the remnant-arc region. This chapter describes field, age, and geochemical data that suggest that a similar rift-edge facies exists in the vicinity of the active arc, on the opposite side of the marginal basin. The rift-edge facies in the active arc setting consists of two main lithotectonic units, herein named informally as the Onion Camp complex and Fiddler Mountain olistostrome. The Onion Camp complex is partly composed of a characteristic metabasalt and red chert association. Red chert yielded scarce radiolarians of Triassic(?) and Early Jurassic age. A distinct chert-pebble conglomerate occurs at scarce localities within metasedimentary rocks. Concordant, composite bodies of amphibolite and serpentinized peridotite represent another distinctive feature of the Onion Camp complex. The metamorphic and lithologic features of the Onion Camp complex are similar to the lower mélange unit of the Rattlesnake Creek terrane, and the units are interpreted to be correlative. The Fiddler Mountain olistostrome is composed of Late Jurassic (Kimmeridgian?) pelagic and hemipelagic rocks interlayered with ophiolite-clast breccia and megabreccia, similar in character to olistostromal deposits associated with the rift-edge facies of the remnant arc. The occurrence of the Rattlesnake Creek terrane and an associated olistostromal deposit within the western Jurassic belt of southwestern Oregon may therefore represent the rift-edge facies in the active arc setting, at the transition between the Rogue–Chetco arc and Josephine ophiolite, further corroborating previous models for the Late Jurassic tectonic evolution of the Klamath Mountains.

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Additional Information:© 2006 Geological Society of America. Manuscript accepted by the Society 10 January 2006. We thank Robert B. Miller and Arthur W. Snoke for their helpful reviews. Many field visits and conversations with Greg Harper were invaluable. Conversations with W.P. Irwin were of great assistance for this study. A 1983 National Association of Geology Teachers summer internship working for W.P. Irwin served as JDY's introduction to the geology of the Klamath Mountains in California; an introduction that sparked interest in the Oregon Klamath Mountains and eventually led to this study. A field visit by L. Ramp in the earliest stages of this project was greatly appreciated. Much of the field mapping in the Kalmiopsis Wilderness could not have been completed without the assistance of B. Yule. We thank B.R. Hacker for obtaining 40Ar/39Ar age determinations and M.O. Mc Williams for the use of his lab at Stanford University. We also thank C. Blome and M. Silk, who kindly made their unpublished radiolarian fossil age determinations available to us. This work was supported by a grant from the Oregon Department of Geology and Mineral Industries, Geological Society of America Research grants nos. 4596-90, 4842-91, and 5089-92 to JDY, by National Science Foundation grants EAR-9117103 and EAR-8720141 to CGB. Contribution 9132 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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Oregon Department of Geology and Mineral IndustriesUNSPECIFIED
Geological Society of America Research Grant4596-90
Geological Society of America Research Grant4842-91
Geological Society of America Research Grant5089-92
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Caltech Division of Geological and Planetary Sciences9132
Series Name:Special papers (Geological Society of America)
Issue or Number:410
Record Number:CaltechAUTHORS:20140821-133048392
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48779
Deposited By: Tony Diaz
Deposited On:22 Aug 2014 06:04
Last Modified:03 Oct 2019 07:07

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