Research Article| March 01, 1987 Petrogenesis of gabbronorite at Yakobi and northwest Chichagof Islands, Alaska GLEN R. HIMMELBERG; GLEN R. HIMMELBERG 1U.S. Geological Survey and Department of Geology, University of Missouri, Columbia, Missouri 65211 Search for other works by this author on: GSW Google Scholar ROBERT A. LONEY; ROBERT A. LONEY 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar PETER I. NABELEK PETER I. NABELEK 3Department of Geology, University of Missouri, Columbia, Missouri 65211 Search for other works by this author on: GSW Google Scholar Author and Article Information GLEN R. HIMMELBERG 1U.S. Geological Survey and Department of Geology, University of Missouri, Columbia, Missouri 65211 ROBERT A. LONEY 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 PETER I. NABELEK 3Department of Geology, University of Missouri, Columbia, Missouri 65211 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (3): 265–279. https://doi.org/10.1130/0016-7606(1987)98<265:POGAYA>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 GLEN R. HIMMELBERG, ROBERT A. LONEY, PETER I. NABELEK; Petrogenesis of gabbronorite at Yakobi and northwest Chichagof Islands, Alaska. GSA Bulletin 1987;; 98 (3): 265–279. doi: https://doi.org/10.1130/0016-7606(1987)98<265:POGAYA>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 On Yakobi Island and at Mirror Harbor on the northwest coast of Chichagof Island, gabbronorite occurs as irregular bodies, as much as 5.5 km in maximum dimension, mostly within a 40 to 43 m.y. composite pluton consisting largely of tonalite. The gab-bronorites are the host rocks for a magmatic nickel-copper sulfide deposit consisting predominantly of pyrrhotite, pentlandite, and chalcopyrite. The gabbronorites characteristically have more orthopyroxene than augite and have a significant amount of hornblende. Rock types mapped as gabbronorite range from hornblende pyroxenite to hornblende-pyroxene gabbronorite to quartz-bearing norite and gabbronorite. The tonalite pluton is composed of hornblende diorite, biotite-hornblende diorite, hornblende quartz diorite, biotite-hornblende tonalite, and biotite granodiorite. Contacts between types of gabbronorite are generally gradational on a scale of centimetres to metres; contacts between gabbronorite and the tonalite pluton are gradational on a scale of metres to tens of metres. Rock textures, pyroxene-hornblende relations, and rock and mineral chemistry of the gabbronorites show systematic changes as the gabbronorites grade into the tonalites. The field, petrographic, and chemical data, including trace-element abundances, of the gabbronorites and tonalite pluton rocks can best be explained by either (1) crystallization of gabbronorite from a tholeiitic magma with subsequent assimilation by tonalite that was simultaneously undergoing fractional crystallization or (2) fractional crystallization of a quartz diorite parent magma yielding the range of gabbronorites and tonalite pluton rocks. 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.