Potassic Feldspar Enrichment in Magma: Origin of Syenite in Deboullie District, Northern Maine

Abstract

Research Article| December 01, 1962 Potassic Feldspar Enrichment in Magma: Origin of Syenite in Deboullie District, Northern Maine GARY M BOONE GARY M BOONE Dept. Geology, The University of Western Ontario, London, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information GARY M BOONE Dept. Geology, The University of Western Ontario, London, Canada Publisher: Geological Society of America Received: 31 May 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): 1451–1476. https://doi.org/10.1130/0016-7606(1962)73[1451:PFEIMO]2.0.CO;2 Article history Received: 31 May 1961 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 GARY M BOONE; Potassic Feldspar Enrichment in Magma: Origin of Syenite in Deboullie District, Northern Maine. GSA Bulletin 1962;; 73 (12): 1451–1476. doi: https://doi.org/10.1130/0016-7606(1962)73[1451:PFEIMO]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 A small composite pluton, the Deboullie stock, comprises a post-orogenic, alkali-calc rock series intrusive into lower Devonian slate. The stock is a partly concordant, partly discordant pluton, and the wall rock structure shows that the magma was forcibly injected. The main intrusives are, from oldest to youngest, pyroxene-biotite syenodiorite and monzonite, pyroxene-hornblende-biotite calc-alkali syenite, and hornblende-biotite granodiorite. Dikes are the fine-grained equivalents of the salic plutonic rocks. Differentiation by fractional crystallization and by upward transfer of H2O and components of potassic feldspar in the melt is proposed as the only satisfactory hypothesis to account for the contrasts in mineralogic evolution. Accordingly, syenitic rocks were derived from the parent magma enriched in potassic feldspar at the top of the magma column; the syenitic magma graded into granodioritic differentiate at deeper levels. The granodioritic magma, richer in plagioclase and quartz, completed the emplacement of the stock by intruding the earlier emplaced calc-alkali syenite.Compositional differences across oscillatory zones in orthoclase and plagioclase feldspars of the main intrusive rocks apparently reflect changes in the partial pressure of volatiles in the melt. Intermittent fracturing of the roof of the magma chamber is appealed to as a cause for the pressure changes and as a mechanism for maintaining a steady-state gradient for H2O and K-bearing components.Neither assimilation, hydrothermal enrichment, nor liquid-crystal reactions involving the mafic minerals adequately explains the abundance of potassic feldspar in the syenite. 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.