Structure, Metamorphism, and Plutonism in the South-Central Klamath Mountains, California

Research Article| August 01, 1965 Structure, Metamorphism, and Plutonism in the South-Central Klamath Mountains, California GREGORY A DAVIS; GREGORY A DAVIS Dept. Geology, University of Southern California, Los Angeles, California Search for other works by this author on: GSW Google Scholar M. J HOLDAWAY; M. J HOLDAWAY Dept. Geology and Geophysics, Southern Methodist University, Dallas, Texas Search for other works by this author on: GSW Google Scholar PETER W LIPMAN; PETER W LIPMAN U. S. Geological Survey, Denver, Colorado Search for other works by this author on: GSW Google Scholar W. D ROMEY W. D ROMEY Dept. Geology, Syracuse University, Syracuse, New York Search for other works by this author on: GSW Google Scholar GSA Bulletin (1965) 76 (8): 933–966. https://doi.org/10.1130/0016-7606(1965)76[933:SMAPIT]2.0.CO;2 Article history received: 22 Apr 1964 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GREGORY A DAVIS, M. J HOLDAWAY, PETER W LIPMAN, W. D ROMEY; Structure, Metamorphism, and Plutonism in the South-Central Klamath Mountains, California. GSA Bulletin 1965;; 76 (8): 933–966. doi: https://doi.org/10.1130/0016-7606(1965)76[933:SMAPIT]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 In the south-central Klamath Mountains 50 miles of the the north-trending central metamorphic belt and adjacent parts of the eastern Paleozoic and western Paleozoic and Triassic belts have been mapped and studied in detail. Within the central metamorphic belt a sequence of three lithologically distinctive metamorphic units has been recognized (from bottom to top): (1) siliceous metasedimentary rocks and greenstones of the Stuart Fork Formation; (2) the Salmon Hornblende Schist; and (3) siliceous, calcareous, and amphibolitic rocks, predominantly metasedimentary, of the Grouse Ridge Formation. The age of these metamorphic rocks is uncertain; they are known only to predate intrusion of Late Jurassic (Nevadan) granitic rocks. Ultramafic rocks, mainly alpine-type peridotites, were emplaced before the granitic rocks and occur primarily in a single large sheetlike body which separates the central metamorphic belt from the eastern Paleozoic belt. Granitic plutons, including quartz diorites, trondhjemites, granodiorites, diorites, and gabbros, in decreasing order of abundance, range in size from less than 1 to about 80 square miles in area.Two orogenic phases in the central metamorphic belt have been distinguished by structural and textural features. A late deformation uniformly affected the metamorphic terrane and the ultramafic rocks but predated granitic rocks. It was accompanied by some metamorphism in the lower to middle greenchist facies and produced upright folds that trend south and plunge gently. An earlier phase affected the various rock units differentially; it produced widespread recumbent folding and upper greenschist- to amphibolite-facies metamorphism in Salmon and Grouse Ridge rocks, but involved the underlying Stuart Fork Formation less severely, producing at least local recumbent folding and lower greenschist-facies metamorphism. The preferred interpretation of this upward increase in structural complexity and metamorphic grade is that the Salmon-Grouse Ridge sequence is a thrust sheet which overrode the Stuart Fork rocks concurrently with emplacement of the ultramafic rocks during the culmination of early recumbent folding and metamorphism. Thrusting was then followed by upright folding during the waning stages of regional metamorphism. The first deformational phase, and possibly the second, occurred during late Paleozoic time as indicated by recent isotopic ages of Salmon Hornblende Schist. 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.