High-fluorine rhyolite: An eruptive pegmatite magma at the Honeycomb Hills, Utah

Abstract

Research Article| November 01, 1988 High-fluorine rhyolite: An eruptive pegmatite magma at the Honeycomb Hills, Utah Roger D. Congdon; Roger D. Congdon 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112-1183 Search for other works by this author on: GSW Google Scholar W. P. Nash W. P. Nash 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112-1183 Search for other works by this author on: GSW Google Scholar Author and Article Information Roger D. Congdon 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112-1183 W. P. Nash 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112-1183 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (11): 1018–1021. https://doi.org/10.1130/0091-7613(1988)016<1018:HFRAEP>2.3.CO;2 Article history First Online: 02 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 Roger D. Congdon, W. P. Nash; High-fluorine rhyolite: An eruptive pegmatite magma at the Honeycomb Hills, Utah. Geology 1988;; 16 (11): 1018–1021. doi: https://doi.org/10.1130/0091-7613(1988)016<1018:HFRAEP>2.3.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 SocietyGeology Search Advanced Search Abstract The Honeycomb Hills rhyolite dome in western Utah displays chemical and mineralogical features characteristic of a rare-element pegmatite magma. The lavas show extreme enrichments in such trace elements as Rb (≤1960 ppm), Cs (≤78), Li (≤344), Sn (≤33), Be (≤270), and Y (≤156). Phenocrysts (10%-50% by volume) include sanidine (Or66-70), plagioclase (Ab83-92), quartz, biotite approaching fluorsiderophyllite, and fluortopaz, as well as accessory phases common to highly differentiated granites and pegmatites, including zircon, thorite, fluocerite, columbite, fergusonite, and samarskite. Low temperatures (600 to 640 °C), coupled with high phenocryst and silica content, might normally preclude eruption due to the extremely high viscosity of the melt. However, high concentrations of fluorine (2%-3%) could domal lavas significantly reduce viscosity and allow eruption of domal lavas even after dewatering of the mama during the initial pyroclastic phase of the eruptive cycle. Fractionation of phenocrysts and accessory phases, for which partition coefficients have been measured, is sufficient to account for most compositional gradients inferred in the preeruptive magma body, although transport by a fluid phase formed a may have caused upward enrichments in Li, Be, and Cs. If the Honeycomb Hills magma had crystallized at depth, it would have formed a rare-element pegmatite. 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.