Ages of Zircons from the Northern Cascade Mountains, Washington

Research Article| December 01, 1972 Ages of Zircons from the Northern Cascade Mountains, Washington JAMES M MATTINSON JAMES M MATTINSON University of California, Santa Barbara, California 93106 AUTHOR'S PRESENT ADDRESS: GEOPHYSICAL LABORATORY, CARNEGIE INSTITUTION OF WASHINGTON, WASHINGTON, D.C. 20008 Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES M MATTINSON AUTHOR'S PRESENT ADDRESS: GEOPHYSICAL LABORATORY, CARNEGIE INSTITUTION OF WASHINGTON, WASHINGTON, D.C. 20008 University of California, Santa Barbara, California 93106 Publisher: Geological Society of America Received: 19 Jan 1972 Revision Received: 24 Apr 1972 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (12): 3769–3784. https://doi.org/10.1130/0016-7606(1972)83[3769:AOZFTN]2.0.CO;2 Article history Received: 19 Jan 1972 Revision Received: 24 Apr 1972 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JAMES M MATTINSON; Ages of Zircons from the Northern Cascade Mountains, Washington. GSA Bulletin 1972;; 83 (12): 3769–3784. doi: https://doi.org/10.1130/0016-7606(1972)83[3769:AOZFTN]2.0.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 Pre-Late Cretaceous crystalline rocks in the core of the Northern Cascade Mountains of Washington are predominantly heterogeneous supracrustal gneiss and schist, and dioritic, quartz dioritic, and trondhjemitic plutons and bodies of orthogneiss. Migmatite derived from plutonic and supracrustal rocks is also widespread. Isotopic age determinations of zircons indicate that, of the supracrustal gneiss and schist, the Swakane Gneiss and possibly the Skagit Gneiss may have been deposited > 1,650 m.y. ago. Alternatively, some of these rocks may be younger but were derived at least in part from a >l,650-m.y.-old source terrane. A second group of supracrustal rocks, the Younger gneissic rocks of the Holden area, includes a metavolcanic unit about 265 m.y. old.Plutonic rocks and orthogneisses comprise four main age groups: 1,452 to 2,000 m.y., pyroxene gneiss of the Yellow Aster Complex; about 460 m.y., the Turtleback Complex of the San Juan Islands and younger orthogneiss of the Yellow Aster Complex; 220 m.y., plutonic and gneissic rocks of the Marblemount belt (Marblemount Meta-Quartz Diorite, Dumbell Mountain plutons); and 92 m.y., the Eldorado Orthogneiss. Strongly metamorphosed rocks of the Chelan Complex, chiefly quartz dioritic, have zircon Pb206/U238 ages ranging from 100 to 183 m.y. These ages appear to be discordant, and the Chelan Complex may represent remobilized rocks from the 220-m.y.-old Marblemount belt.Ages of metamorphic minerals, zircons from pegmatitic material associated with migmatite, and zircons from synkinematic intrusive rocks indicate two major episodes of metamorphism in the Northern Cascade terrane, one about 415 m.y. ago and the other, 60 to 90 m.y. ago. Both episodes culminated in metamorphism to amphibolite facies grade—and in the case of the older episode, metamorphism to granulite facies grade—and both resulted in extensive migmatization of pre-existing rocks. 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.