Detrital zircon geochronology and the provenance of the Harmony and Valmy Formations, Roberts Mountains allochthon, Nevada

Abstract

Research Article| July 01, 1994 Detrital zircon geochronology and the provenance of the Harmony and Valmy Formations, Roberts Mountains allochthon, Nevada MOIRA SMITH; MOIRA SMITH 1Department of Geosciences University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar GEORGE GEHRELS GEORGE GEHRELS 1Department of Geosciences University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Author and Article Information MOIRA SMITH 1Department of Geosciences University of Arizona, Tucson, Arizona 85721 GEORGE GEHRELS 1Department of Geosciences University of Arizona, Tucson, Arizona 85721 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1994) 106 (7): 968–979. https://doi.org/10.1130/0016-7606(1994)106<0968:DZGATP>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 MailTo Tools Icon Tools Get Permissions Search Site Citation MOIRA SMITH, GEORGE GEHRELS; Detrital zircon geochronology and the provenance of the Harmony and Valmy Formations, Roberts Mountains allochthon, Nevada. GSA Bulletin 1994;; 106 (7): 968–979. doi: https://doi.org/10.1130/0016-7606(1994)106<0968:DZGATP>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 A long-standing debate over the provenance of lower Paleozoic sedimentary rocks in the Roberts Mountains allochthon, Nevada, is addressed through abraded single-grain U-Pb detrital zircon analysis of the Harmony and Vahny Formations. Twenty-seven zircon grains from mature quartz arenite of the Middle Ordovician Valmy Formation yielded concordant to a few percent discordant ages of ∼1050 Ma (n = 2),1830-1845 Ma (n = 4),1910-1960 Ma (n = 5),2270-2340 Ma (n = 2), 2650-2750 Ma (n = 8), and ∼2900 Ma (n =1), and moderately discordant ages of ∼2070 Ma (n =1) and ∼3240 Ma (n =1). These ages are consistent with ultimate derivation from the north (Slave craton and Medicine Hat province and central/northern Alberta) and suggest a link between the Valmy Formation and the coeval Eureka Quartzite on the adjacent shelf and miogeoclinal prism. Twenty-seven analyses of zircon from immature quartzo-feldspathic wacke of the Upper Cambrian Harmony Formation include concordant analyses in the range of 695-710 Ma (n = 9), 1015-1225 Ma (n = 12), ∼1330 Ma (n = 2), ∼1745 Ma (n = 1), ∼1915 Ma (n = 1), and 2570 Ma (n = 1). The ∼700 Ma and ∼1100 Ma ages (which represent >80 %of the grains) have no known western North American basement source of reasonable proximity and age, suggesting derivation from an unknown western or southern source, or perhaps from rocks that presently underlie the Roberts Mountains allochthon.A growing body of U-Pb isotopic evidence indicates that 1000-1270 Ma and 670-750 Ma zircon ages are relatively common in offshelf continental margin strata. The latter set of ages is also represented by orthogneiss that intrudes or is overlain by continental margin strata, necessitating the widespread exposure of felsic plutonic rocks of these ages along the Cordilleran margin during early Paleozoic time. Subsequently, such rocks may have been overlain by younger continental margin strata, structurally overlain by allochthonous units, or tectonically removed from the region by younger rifting events. The presence of widespread mid- and late Proterozoic felsic magmatic rocks along the Cordilleran margin is not easily accommodated by popular pre-570 Ma plate reconstructions that place Nevada and the central Cordillera opposite the Transantarctic Mountains or eastern Australia. 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.