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Time relations and structural-stratigraphic patterns in ophiolite accretion, west central Klamath Mountains, California

Saleeby, Jason and Harper, Gregory D. and Snoke, Arthur W. and Sharp, Warren D. (1982) Time relations and structural-stratigraphic patterns in ophiolite accretion, west central Klamath Mountains, California. Journal of Geophysical Research B, 87 (B5). pp. 3831-3848. ISSN 0148-0227. doi:10.1029/JB087iB05p03831.

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New geochronological data and published structural and stratigraphic data show that two distinctly different ophiolitic assemblages formed in general proximity to one another at nearly the same time and were subsequently imbricated along a regional thrust zone. The Josephine ophiolite constitutes a complete oceanic crust and upper mantle sequence which lies within the western Jurassic belt of the Klamath province. Within the study area the Josephine ophiolite was formed by seafloor spreading at about 157 m.y. before present. It was immediately covered by a thin pelagic and hemipelagic sequence which grades into a thick flysch sequence, both of which comprise the Galice Formation. The Galice flysch was derived from volcanic arc and uplifted continental margin orogenic assemblages. A major nonvolcanic source for the Galice flysch appears to have been the western Paleozoic and Triassic belt of the Klamath province exposed to the east. Proximal volcanic arc activity migrated to the site of the Josephine-Galice section by 151 m.y. and is represented by numerous dikes and sills which intrude the ophiolite and Galice Formation. The Preston Peak ophiolite is a polygenetic assemblage consisting of (1) a pre-mid-Jurassic tectonitic peridotite-amphibolite substrate which represents disrupted and unroofed basement of the western Paleozoic and Triassic belt and (2) an upper mafic complex which was intruded through and constructed above the tectonite substrate at about 160 m.y. The mafic complex consists primarily of diabase hypabyssal rocks that are overlain by diabase-clast breccia and hemipelagic deposits. A major arc-plutonic complex was emplaced into the Preston Peak ophiolite in at least two pulses at 153 and 149 m.y. Major phases of this complex consist of wehrlite, gabbro, pyroxene diorite, and hornblende diorite. The Josephine ophiolite is interpreted as the remnants of interarc basin crust. The Preston Peak ophiolite is interpreted as either a primitive remnant arc complex or a rift edge facies for the Josephine interarc basin. The Galice Formation represents a submarine fan complex that was built on juvenile crust of the Josephine basin floor. During the time interval of 153 to 149 m.y. the locus or arc magmatism migrated to an area which included the interarc basin floor and the remnant arc or basin edge. The basin shortly thereafter closed by convergent tectonics during the Nevadan orogeny resulting in the imbrication of the Josephine and Preston Peak ophiolites and their superimposed arc assemblages. The transition from seafloor spreading generation of Josephine ophiolite to its tectonic accretion by convergence and basin closure occurred within 5 to 10 m.y. The process of rifting and ophiolite formation in series with convergence and ophiolite accretion is considered an important mechanism for generating and displacing allocthonous terranes in the Klamath Mountains-Sierra Nevada region, and perhaps throughout the western cordillera.

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Additional Information:© 1982 by the American Geophysical Union. Received May 20, 1981; revised January 6, 1982; accepted January 8, 1982. Paper number 2B0050. Conversations and written communications with W. P. Irwin and D. L. Jones were of great assistance for this study, and critical reviews by R. G. Coleman and J. E. Wright were helpful. Support from NSF grant EAR 7925998 is gratefully acknowledged by J. B. Saleeby. A. W. Snoke gratefully acknowledges a faculty research grant from the University of South Carolina that partially supported field expenses during this study. We would also like to thank C. D. Ando, J. E. Quick, and C. J. SunRidge-Saleeby for helping us pack out the large zircon sample from Preston Peak. C. J. SunRidge-Saleeby is also acknowledged for patience and expertise in final hand purification of zircon separates. Contribution 3618 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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NSFEAR 7925998
University of South CarolinaUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences3618
Issue or Number:B5
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Official Citation:Saleeby, J. B., G. D. Harper, A. W. Snoke, and W. D. Sharp (1982), Time relations and structural-stratigraphic patterns in ophiolite accretion, west central Klamath Mountains, California, J. Geophys. Res., 87(B5), 3831–3848, doi:10.1029/JB087iB05p03831
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48904
Deposited By: Tony Diaz
Deposited On:26 Aug 2014 20:04
Last Modified:14 Jul 2022 18:14

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