Structure, petrology, and metamorphic history of the Nome Group blueschist terrane, Salmon Lake area, Seward Peninsula, Alaska

Abstract

Research Article| May 01, 1985 Structure, petrology, and metamorphic history of the Nome Group blueschist terrane, Salmon Lake area, Seward Peninsula, Alaska STEPHEN POLLOCK THURSTON STEPHEN POLLOCK THURSTON 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 and Chevron U.S.A. Inc., Concord, California 94524 Search for other works by this author on: GSW Google Scholar Author and Article Information STEPHEN POLLOCK THURSTON 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 and Chevron U.S.A. Inc., Concord, California 94524 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (5): 600–617. https://doi.org/10.1130/0016-7606(1985)96<600:SPAMHO>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 STEPHEN POLLOCK THURSTON; Structure, petrology, and metamorphic history of the Nome Group blueschist terrane, Salmon Lake area, Seward Peninsula, Alaska. GSA Bulletin 1985;; 96 (5): 600–617. doi: https://doi.org/10.1130/0016-7606(1985)96<600:SPAMHO>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 An 80-mi2 area adjacent to Salmon Lake, mapped at a scale of 1:36,680, includes a section of the Nome Group schist that is at least 2,000 m thick. It is relatively intact, with relict primary lithologic layering, and not mélange-like or highly disrupted by faults. The Nome Group metasediments include pelitic schist, graphitic quartzite, pure and impure marble, calcareous schist, chlorite-albite schist, chloritic quartz-albite, and mafic schists. Metaigneous rocks include Fe-Ti-rich metabasite and granitic to tonalitic orthogneiss. The protoliths are Precambrian(?) to Paleozoic in age, and radiometric ages indicate that the high-pressure metamorphism of the Nome Group is Late Jurassic. Blueschist-facies assemblages occur in Nome Group metabasites and in most metasedimentary schists. The blueschists are synkinematic; they formed during an episode of widely distributed penetrative deformation and mesoscopic intrafolial isoclinal folding of consistent orientation. The Nome Group of the Salmon Lake area underwent a prograde monocyclic polyfacial high-P/T metamorphism. Initial metamorphism was in the lower-T regime of the lawsonite-glaucophane field (300 °C, 7 kb?) and prograded with increasing T and P into the epidote-almandine-glaucophane field through an apparent P/T maximum, as indicated by the assemblage glaucophane-omphacite-garnet (420 °C, 9–10 kb). The later stages of the metamorphism were characterized by increased T/P, likely during initial stages of decompression and the return of the “normal” geothermal gradient, to the transition between the blueschist facies and the high-P albite-epiclote-barroisite field (450 to 525 °C, 7–8 kb?). This high-P/T cycle was followed by an incipient static retrogressive metamorphism at low greenschist-facies conditions during the later uplift of the Nome Group in the Late Cretaceous and early Tertiary. 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.