Strontium isotopes and magma dynamics: Insights from high-temperature rhyolites

Research Article| October 01, 2011 Strontium isotopes and magma dynamics: Insights from high-temperature rhyolites John A. Wolff; John A. Wolff 1School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA Search for other works by this author on: GSW Google Scholar Ben S. Ellis; Ben S. Ellis 1School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA Search for other works by this author on: GSW Google Scholar Frank C. Ramos Frank C. Ramos 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Search for other works by this author on: GSW Google Scholar Author and Article Information John A. Wolff 1School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA Ben S. Ellis 1School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA Frank C. Ramos 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Publisher: Geological Society of America Received: 11 Jan 2011 Revision Received: 26 Apr 2011 Accepted: 30 Apr 2011 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (10): 931–934. https://doi.org/10.1130/G32062.1 Article history Received: 11 Jan 2011 Revision Received: 26 Apr 2011 Accepted: 30 Apr 2011 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation John A. Wolff, Ben S. Ellis, Frank C. Ramos; Strontium isotopes and magma dynamics: Insights from high-temperature rhyolites. Geology 2011;; 39 (10): 931–934. doi: https://doi.org/10.1130/G32062.1 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 Volcanic rocks often exhibit internal heterogeneity in radiogenic isotopes. Isotopic disequilibrium between coexisting phenocrysts and isotopic zoning within single crystals has been demonstrated in basalts, andesites, dacites, and rhyolites. High-temperature Snake River–type rhyolites appear to be an exception. Despite the occurrence of Snake River Plain rhyolites in a region of isotopically highly variable crust and mantle, and significant differences from rhyolite unit to rhyolite unit, little to no Sr isotopic zoning is found within their feldspar phenocrysts, and feldspars within a single unit define tightly grouped unimodal populations. High-temperature rhyolitic magmas possess a unique combination of temperature and melt viscosity. Although typically 200 °C hotter than common rhyolites, the temperature effect on viscosity is offset by lower water contents (<3.5 wt%), so melt viscosities are in the same range as common, water-rich, cool rhyolites (105–106 Pa s). However, magmatic temperatures are in the same range as basaltic andesites and andesites; consequently, cation diffusion rates are orders of magnitude greater than common rhyolites. We hypothesize that this combination of characteristics promotes crystal isotopic homogeneity: viscosities are too high to permit crystal transfer between liquids of contrasting 87Sr/86Sr on time scales shorter than those required for diffusive homogenization of Sr within phenocrysts (500–10,000 yr). This is not true for most magma types, in which crystal transfer is rapid (<<100 yr) due to low melt viscosities (basalts and intermediate magmas), or Sr diffusion rates are so slow that equilibration times are longer than the lifetime of the system (e.g., cool, wet rhyolites: 105–106 yr). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.