Compositional layers in the zoned magma chamber of the Grizzly Peak Tuff

Abstract

Research Article| April 01, 1987 Compositional layers in the zoned magma chamber of the Grizzly Peak Tuff Christopher J. Fridrich; Christopher J. Fridrich 1Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Gail A. Mahood Gail A. Mahood 1Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Author and Article Information Christopher J. Fridrich 1Department of Geology, Stanford University, Stanford, California 94305 Gail A. Mahood 1Department of Geology, Stanford University, Stanford, California 94305 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1987) 15 (4): 299–303. https://doi.org/10.1130/0091-7613(1987)15<299:CLITZM>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Christopher J. Fridrich, Gail A. Mahood; Compositional layers in the zoned magma chamber of the Grizzly Peak Tuff. Geology 1987;; 15 (4): 299–303. doi: https://doi.org/10.1130/0091-7613(1987)15<299:CLITZM>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 SocietyGeology Search Advanced Search Abstract The 34 Ma Grizzly Peak Tuff in west-central Colorado preserves evidence for distinct compositional layers in a high-level magma chamber. Intracaldera tuff consists of a single cooling unit, at least 2.7 km thick, zoned from a high-silica rhyolite base to an eroded low-silica rhyolite top. Two horizons of heterogeneous tuff beneath wedges of caldera-collapse breccia contain fiamme of dacite to mafic latite along with the rhyolitic fiamme that make up the rest of the tuff. Compositional zoning defined by fiamme is a step function rather than a continuous gradient. Seven petrographic groups of fiamme each have distinct compositions separated by compositional gaps. As the same clusters and gaps are found in collections of fiamme from widely separated stratigraphic levels, step-function zoning must be intrinsic to the chamber rather than a consequence of the tapping process. We interpret the seven fiamme groups as seven separately converting layers in a density-stratified magma reservoir tapped by eruption of the Grizzly Peak Tuff. Excluding the thin heterogeneous tuff horizons, ∼3 km of caldera fill is drawn from the three most silicic layers, suggesting that the three rhyolitic layers were each at least 1 km thick in the magma chamber. 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.