Age and tectonic setting of the Mesozoic McCoy Mountains Formation in western Arizona, USA

Abstract

Research Article| July 01, 2011 Age and tectonic setting of the Mesozoic McCoy Mountains Formation in western Arizona, USA Jon E. Spencer; Jon E. Spencer * 1Arizona Geological Survey, 416 W. Congress Street, #100, Tucson, Arizona 85701, USA *E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar Stephen M. Richard; Stephen M. Richard † 1Arizona Geological Survey, 416 W. Congress Street, #100, Tucson, Arizona 85701, USA †E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar George E. Gehrels; George E. Gehrels § 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA §E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar James D. Gleason; James D. Gleason # 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA #E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar William R. Dickinson William R. Dickinson ** 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA **E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar Author and Article Information Jon E. Spencer * 1Arizona Geological Survey, 416 W. Congress Street, #100, Tucson, Arizona 85701, USA Stephen M. Richard † 1Arizona Geological Survey, 416 W. Congress Street, #100, Tucson, Arizona 85701, USA George E. Gehrels § 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA James D. Gleason # 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA William R. Dickinson ** 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA *E-mail: [e-mail] †E-mail: [e-mail] §E-mail: [e-mail] #E-mail: [e-mail] **E-mail: [e-mail] Publisher: Geological Society of America Received: 22 Oct 2009 Revision Received: 20 Apr 2010 Accepted: 20 May 2010 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2011 Geological Society of America GSA Bulletin (2011) 123 (7-8): 1258–1274. https://doi.org/10.1130/B30206.1 Article history Received: 22 Oct 2009 Revision Received: 20 Apr 2010 Accepted: 20 May 2010 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Jon E. Spencer, Stephen M. Richard, George E. Gehrels, James D. Gleason, William R. Dickinson; Age and tectonic setting of the Mesozoic McCoy Mountains Formation in western Arizona, USA. GSA Bulletin 2011;; 123 (7-8): 1258–1274. doi: https://doi.org/10.1130/B30206.1 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 The McCoy Mountains Formation consists of Upper Jurassic to Upper Cretaceous siltstone, sandstone, and conglomerate exposed in an east-west–trending belt in southwestern Arizona and southeastern California. At least three different tectonic settings have been proposed for McCoy deposition, and multiple tectonic settings are likely over the ∼80 m.y. age range of deposition. U-Pb isotopic analysis of 396 zircon sand grains from at or near the top of McCoy sections in the southern Little Harquahala, Granite Wash, New Water, and southern Plomosa Mountains, all in western Arizona, identified only Jurassic or older zircons. A basaltic lava flow near the top of the section in the New Water Mountains yielded a U-Pb zircon date of 154.4 ± 2.1 Ma. Geochemically similar lava flows and sills in the Granite Wash and southern Plomosa Mountains are inferred to be approximately the same age. We interpret these new analyses to indicate that Mesozoic clastic strata in these areas are Upper Jurassic and are broadly correlative with the lowermost McCoy Mountains Formation in the Dome Rock, McCoy, and Palen Mountains farther west. Six samples of numerous Upper Jurassic basaltic sills and lava flows in the McCoy Mountains Formation in the Granite Wash, New Water, and southern Plomosa Mountains yielded initial εNd values (at t = 150 Ma) of between +4 and +6. The geochemistry and geochronology of this igneous suite, and detrital-zircon geochronology of the sandstones, support the interpretation that the lower McCoy Mountains Formation was deposited during rifting within the western extension of the Sabinas-Chihuahua-Bisbee rift belt. Abundant 190–240 Ma zircon sand grains were derived from nearby, unidentified Triassic magmatic-arc rocks in areas that were unaffected by younger Jurassic magmatism. A sandstone from the upper McCoy Mountains Formation in the Dome Rock Mountains (Arizona) yielded numerous 80–108 Ma zircon grains and almost no 190–240 Ma grains, revealing a major reorganization in sediment-dispersal pathways and/or modification of source rocks that had occurred by ca. 80 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.