Age of emplacement of the Okanogan gneiss dome, north-central Washington

Abstract

Research Article| September 01, 1976 Age of emplacement of the Okanogan gneiss dome, north-central Washington K. F. FOX, JR.; K. F. FOX, JR. 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar C. D. RINEHART; C. D. RINEHART 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar J. C. ENGELS; J. C. ENGELS 2348 Waverly Street, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar T. W. STERN T. W. STERN 3U.S. Geological Survey, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Author and Article Information K. F. FOX, JR. 1U.S. Geological Survey, Menlo Park, California 94025 C. D. RINEHART 1U.S. Geological Survey, Menlo Park, California 94025 J. C. ENGELS 2348 Waverly Street, Menlo Park, California 94025 T. W. STERN 3U.S. Geological Survey, Reston, Virginia 22092 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (9): 1217–1224. https://doi.org/10.1130/0016-7606(1976)87<1217:AOEOTO>2.0.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 K. F. FOX, C. D. RINEHART, J. C. ENGELS, T. W. STERN; Age of emplacement of the Okanogan gneiss dome, north-central Washington. GSA Bulletin 1976;; 87 (9): 1217–1224. doi: https://doi.org/10.1130/0016-7606(1976)87<1217:AOEOTO>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 Contact relations and internal fabric suggest that penetrative metamorphism and deformation of parental rocks of the Okanogan gneiss dome culminated in their mobilization and diapiric intrusion into the country rocks. The gneiss dome cuts both plutonic rocks and eugeosynclinal low-grade metamorphic rocks, including rocks as young as Late Triassic, but not adjacent sedimentary deposits and associated volcanic rocks of Eocene age. The gneiss dome is itself cut by the Swimptkin Creek pluton, an epizonal quartz monzonite body that yields concordant biotite and hornblende K-Ar ages of 48.0 and 48.2 m.y. (Eocene), respectively. Thus, the field relations bracket the age of emplacement of the gneiss dome between Late Triassic and Eocene time.A total of 21 age determinations were made using samples from seven localities within the gneiss dome. Zircon dated by U-Th-Pb methods gave the oldest ages, including Pb206/U238 and Pb207/U235 ages of 87.3 and 100.0 m.y., respectively. Fission-track ages of 66 m.y. (sphene), 63 m.y. (epidote), 59 m.y. (allanite), 53 m.y. (apatite), and 51 m.y. (apatite) were obtained, along with K-Ar ages ranging from 58 m.y. (hornblende) to 46 m.y. (biotite).These data suggest that the gneiss dome was emplaced in Late Cretaceous time — probably between roughly 87 and 65 m.y. ago — then cooled slowly through the successive temperature thresholds for sphene, epidote-allanite, hornblende, and finally apatite-muscovite-biotite, below which either loss of argon or erasure of fission tracks ceased. 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.