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An expanded view of Jurassic orogenesis in the western United States Cordillera: Middle Jurassic (pre-Nevadan) regional metamorphism and thrust faulting within an active arc environment, Klamath Mountains, California

1988; Geological Society of America; Volume: 100; Issue: 6 Linguagem: Inglês

10.1130/0016-7606(1988)100 2.3.co;2

1943-2674

James E. Wright, MARK R. FAHAN,

High-pressure geophysics and materials

Research Article| June 01, 1988 An expanded view of Jurassic orogenesis in the western United States Cordillera: Middle Jurassic (pre-Nevadan) regional metamorphism and thrust faulting within an active arc environment, Klamath Mountains, California JAMES E. WRIGHT; JAMES E. WRIGHT 1Department of Geology, Stanford University, Stanford California 94305 Search for other works by this author on: GSW Google Scholar MARK R. FAHAN MARK R. FAHAN 2Holguin & Associates, Inc., 73 North Palm Street, Ventura, California 93001 Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES E. WRIGHT 1Department of Geology, Stanford University, Stanford California 94305 MARK R. FAHAN 2Holguin & Associates, Inc., 73 North Palm Street, Ventura, California 93001 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1988) 100 (6): 859–876. https://doi.org/10.1130/0016-7606(1988)100 2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JAMES E. WRIGHT, MARK R. FAHAN; An expanded view of Jurassic orogenesis in the western United States Cordillera: Middle Jurassic (pre-Nevadan) regional metamorphism and thrust faulting within an active arc environment, Klamath Mountains, California. GSA Bulletin 1988;; 100 (6): 859–876. doi: https://doi.org/10.1130/0016-7606(1988)100 2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Basaltic to basaltic andesitic volcaniclastic rocks and their contemporaneous mafic-ultramafic intrusive complexes delineate a Middle Jurassic arc terrane within the Klamath Mountain province of northern California. Exposures of the supracrustal volcaniclastic rocks are restricted to a single fault-bounded terrane, but the deeper level intrusive complexes were emplaced into most, if not all, the pre-Late Jurassic terranes of the Klamath Mountain region. The pre-Late Jurassic terranes thus constitute the basement of the Middle Jurassic arc. U-Pb zircon analyses of 39 zircon fractions from 12 intrusive complexes plus K-Ar dating of the volcaniclastic strata demonstrate magmatic activity over the interval of ∼177-159 Ma. The active arc and its basement were imbricated by a compressive deformational event, the signature of which included thrust faulting, isoclinal folding, and regional metamorphism. Several diverse lines of evidence, including K-Ar dating of metamorphic rocks, crosscutting relations of dated intrusive complexes to thrust faults, and U-Pb dating of synmetamorphic intrusive complexes, establish a distinctly pre-Nevadan Middle Jurassic age (ongoing at ∼169 Ma and over by at least 161 Ma) for this compressive deformational episode. "Outboard" and structurally beneath the Middle Jurassic arc and its basement are several terranes that collectively comprise the western Jurassic belt. These terranes were deformed and regionally metamorphosed during the Late Jurassic Nevadan orogeny, which occurred within the time interval of ∼157-150 Ma, as Upper Jurassic plutons with 150- to 142-m.y.-old zircon ages have contact aureoles that overprint the Nevadan fabric, and the ∼157-m.y.-old Rogue Formation was deformed in the Nevadan event. The Middle and Late Jurassic compressive deformational events were thus distinct and separated by as much as 15-20 m.y. The relation between Middle and Late Jurassic magmatism and deformation suggests that the Klamath Mountain province records the evolution of a considerably long-lived arc system that evolved above an east-dipping subduction zone. In addition, we suggest that this are system may represent an oceanic continuation of the long-recognized early Mesozoic arc terrane of the western U.S. Cordillera. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.