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Uranium-Lead Ages of Minerals from the Stillwater Igneous Complex and Associated Rocks, Montana

1971; Geological Society of America; Volume: 82; Issue: 8 Linguagem: Inglês

10.1130/0016-7606(1971)82[2231

1943-2674

P. D. Nunes, G. R. Tilton,

Geological and Geochemical Analysis

Research Article| August 01, 1971 Uranium-Lead Ages of Minerals from the Stillwater Igneous Complex and Associated Rocks, Montana PAUL D NUNES; PAUL D NUNES Department of Geological Sciences, University of California, Santa Barbara, California 93106 PRESENT ADDRESS: (NUNES) INSTITUT FUR KRISTALLO-GRAPHIE UND PETROGRAPHIE, EIDG. TECHNISCHE HOCHSCHULE, 8006 ZURICH, SWITZERLAND Search for other works by this author on: GSW Google Scholar GEORGE R TILTON GEORGE R TILTON Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar Author and Article Information PAUL D NUNES PRESENT ADDRESS: (NUNES) INSTITUT FUR KRISTALLO-GRAPHIE UND PETROGRAPHIE, EIDG. TECHNISCHE HOCHSCHULE, 8006 ZURICH, SWITZERLAND Department of Geological Sciences, University of California, Santa Barbara, California 93106 GEORGE R TILTON Department of Geological Sciences, University of California, Santa Barbara, California 93106 Publisher: Geological Society of America Received: 04 Jan 1971 Revision Received: 05 Apr 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, 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 (1971) 82 (8): 2231–2250. https://doi.org/10.1130/0016-7606(1971)82[2231:UAOMFT]2.0.CO;2 Article history Received: 04 Jan 1971 Revision Received: 05 Apr 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation PAUL D NUNES, GEORGE R TILTON; Uranium-Lead Ages of Minerals from the Stillwater Igneous Complex and Associated Rocks, Montana. GSA Bulletin 1971;; 82 (8): 2231–2250. doi: https://doi.org/10.1130/0016-7606(1971)82[2231:UAOMFT]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 Nineteen U-Pb zircon analyses from the Still-water complex basal zone and associated rocks are interpreted as meaning: (1) the Stillwater igneous complex was emplaced about 2,750 m.y. ago; (2) there is little recorded time difference (less than 60 m.y.) between intrusion of the Stillwater complex and emplacement of siliceous igneous rocks at the southeastern end of the complex; (3) the Stillwater complex intruded sediments or metasediments containing approximately 3,140 m.y. old (or older) zircons; and (4) the Stillwater complex contact metamorphism did not reset U-Pb clock in zircons from exposed hornfels, although hornfels zircons appear to have lost from about 10 to 40 percent of their lead due to intrusion of the complex. The discordant zircon data appear to be best explained with an episodic lead loss mechanism; lead having been lost about 2,750 and 100 m.y. ago. The possibilities, however, of uranium gain at these times, or some continuous diffusion lead loss, or both, may not be excluded.Four apatite U-Pb analyses suggest apatite in the Stillwater complex vicinity lost lead or gained uranium about, 1,600 m.y. ago during an event that did not significantly influence the zircon ages.U-Th-Pb data from Mouat quartz monzonite magnetite indicate either uranium and thorium are heterogeneously distributed in the magnetite and/or uranium and thorium are very susceptible to laboratory acid leaching.Limited plagioclase data did not yield useful age information; rather they showed that the lead isotopic compositions of the Stillwater complex anorthosite have been disturbed since the complex was emplaced. 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.