Hornblendes Formed During Progressive Metamorphism Of Amphibolites, Northwest Adirondack Mountains, New York

Research Article| December 01, 1962 Hornblendes Formed During Progressive Metamorphism Of Amphibolites, Northwest Adirondack Mountains, New York A. E. J ENGEL; A. E. J ENGEL University of California, La Jolla, Calif Search for other works by this author on: GSW Google Scholar CELESTE G ENGEL CELESTE G ENGEL U.S. Geological Survey, La Jolla, Calif Search for other works by this author on: GSW Google Scholar Author and Article Information A. E. J ENGEL University of California, La Jolla, Calif CELESTE G ENGEL U.S. Geological Survey, La Jolla, Calif Publisher: Geological Society of America Received: 27 Nov 1961 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1962, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1962) 73 (12): 1499–1514. https://doi.org/10.1130/0016-7606(1962)73[1499:HFDPMO]2.0.CO;2 Article history Received: 27 Nov 1961 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation A. E. J ENGEL, CELESTE G ENGEL; Hornblendes Formed During Progressive Metamorphism Of Amphibolites, Northwest Adirondack Mountains, New York. GSA Bulletin 1962;; 73 (12): 1499–1514. doi: https://doi.org/10.1130/0016-7606(1962)73[1499:HFDPMO]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 Hornblendes in amphibolite interlayers in the paragneiss of the northwest Adirondack Mountains undergo systematic changes in color, composition, and density during progressive metamorphism from almandine-amphibolite to hornblende-granulite facies. In contrast, indices of refraction of the hornblendes remain about constant.In the almandine-amphibolite facies the amphibolite layers have the bulk composition of a saturated basalt and consist of bluish-green hornblende, andesine, and quartz. As these layers are traced into the hornblende-granulite facies, their composition undergoes a progressive change to that of an olivine basalt with brownish-green hornblende, clinopyroxene and orthopyroxene, and calcic andesine as major constituents.Compositional changes in the hornblendes with increasing grade of metamorphism include increases in Ti, Na, K, Cr, V, and Sc. Decreases occur in the amounts of Mn, Zn, OH + F + Cl, and in the ratios Fe2O3/FeO and Fe/Mg.Density of the hornblendes increases from 3.260 to 3.278 with the increasing grade of metamorphism.These changes in the hornblendes with increasing T and P, although well denned, are less pronounced than those measured in biotites and garnets of the enclosing paragneiss. Large variations in the physical and chemical properties of hornblendes in metamafic rocks reconstituted above the epidote-amphibolite facies appear to be induced principally by critical changes in the bulk composition of the total rock, and not by the regional gradients in T, P, or by changes in kind, or composition, of the coexisting minerals. 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.