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Composite Sunrise Butte pluton: Insights into Jurassic–Cretaceous collisional tectonics and magmatism in the Blue Mountains Province, northeastern Oregon

By
Kenneth Johnson
Kenneth Johnson
Department of Natural Sciences, University of Houston–Downtown, 1 Main Street, Houston, Texas 77002, USA
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Joshua J. Schwartz
Joshua J. Schwartz
Department of Geological Sciences, California State University–Northridge, 18111 Nordhoff Street, Northridge, California 91330, USA
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Jiří Žák
Jiří Žák
Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic
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Kryštof Verner
Kryštof Verner
Czech Geological Survey, Klárov 3, Prague, 11821, Czech Republic, and Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic
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Calvin G. Barnes
Calvin G. Barnes
Department of Geosciences, Texas Tech University, MS 1053, Lubbock, Texas 79409-1053, USA
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Clay Walton
Clay Walton
Department of Geosciences, Texas Tech University, MS 1053, Lubbock, Texas 79409-1053, USA
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Joseph L. Wooden
Joseph L. Wooden
U.S. Geological Survey–Stanford Ion Microprobe Laboratory, Stanford University, Stanford, California 94305-2220, USA
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James E. Wright
James E. Wright
Department of Geology, University of Georgia, 210 Field Street, Athens, Georgia 30602-2501, USA
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Ronald W. Kistler
Ronald W. Kistler
U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA
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Published:
December 01, 2015

The composite Sunrise Butte pluton, in the central part of the Blue Mountains Province, northeastern Oregon, preserves a record of subduction-related magmatism, arc-arc collision, crustal thickening, and deep-crustal anatexis. The earliest phase of the pluton (Desolation Creek unit) was generated in a subduction zone environment, as the oceanic lithosphere between the Wallowa and Olds Ferry island arcs was consumed. Zircons from this unit yielded a 206Pb/238U age of 160.2 ± 2.1 Ma. A magmatic lull ensued during arc-arc collision, after which partial melting at the base of the thickened Wallowa arc crust produced siliceous magma that was emplaced into metasedimentary rocks and serpentinite of the overthrust forearc complex. This magma crystallized to form the bulk of the Sunrise Butte composite pluton (the Sunrise Butte unit; 145.8 ± 2.2 Ma). The heat necessary for crustal anatexis was supplied by coeval mantle-derived magma (the Onion Gulch unit; 147.9 ± 1.8 Ma).

The lull in magmatic activity between 160 and 148 Ma encompasses the timing of arc-arc collision (159–154 Ma), and it is similar to those lulls observed in adjacent areas of the Blue Mountains Province related to the same shortening event. Previous researchers have proposed a tectonic link between the Blue Mountains Province and the Klamath Mountains and northern Sierra Nevada Provinces farther to the south; however, timing of Late Jurassic deformation in the Blue Mountains Province predates the timing of the so-called Nevadan orogeny in the Klamath Mountains. In both the Blue Mountains Province and Klamath Mountains, the onset of deep-crustal partial melting initiated at ca. 148 Ma, suggesting a possible geodynamic link. One possibility is that the Late Jurassic shortening event recorded in the Blue Mountains Province may be a northerly extension of the Nevadan orogeny. Differences in the timing of these events in the Blue Mountains Province and the Klamath–Sierra Nevada Provinces suggest that shortening and deformation were diachronous, progressing from north to south. We envision that Late Jurassic deformation may have collapsed a Gulf of California–style oceanic extensional basin that extended from the Klamath Mountains (e.g., Josephine ophiolite) to the central Blue Mountains Province, and possibly as far north as the North Cascades (i.e., the coeval Ingalls ophiolite).

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GSA Special Papers

Late Jurassic Margin of Laurasia–A Record of Faulting Accommodating Plate Rotation

Thomas H. Anderson
Thomas H. Anderson
Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Alexei N. Didenko
Alexei N. Didenko
Institute of Tectonics and Geophysics, Far Eastern Branch Russian Academy of Sciences, Khabarovsk 680000, Russia, and Geological Institute, Russian Academy of Science, Moscow 119017, Russia
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Cari L. Johnson
Cari L. Johnson
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
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Alexander I. Khanchuk
Alexander I. Khanchuk
Far East Geological Institute, Far Eastern Branch Russian Academy of Sciences, 159, Prospekt 100-letiya Vladivostoku, Vladivostok 690022, Russia
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James H. MacDonald, Jr.
James H. MacDonald, Jr.
Department of Marine and Ecological Sciences, Florida Gulf Coast University, Fort Myers, Florida 33965, USA
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Geological Society of America
Volume
513
ISBN print:
9780813725130
Publication date:
December 01, 2015

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