Sr isotope disequilibrium during differentiation of the Bandelier Tuff: Constraints on the crystallization of a large rhyolitic magma chamber

Research Article| June 01, 1999 Sr isotope disequilibrium during differentiation of the Bandelier Tuff: Constraints on the crystallization of a large rhyolitic magma chamber J. A. Wolff; J. A. Wolff 1Department of Geology, Washington State University, Pullman, Washington 99164, USA Search for other works by this author on: GSW Google Scholar F. C. Ramos; F. C. Ramos 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA Search for other works by this author on: GSW Google Scholar J. P. Davidson J. P. Davidson 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA Search for other works by this author on: GSW Google Scholar Geology (1999) 27 (6): 495–498. https://doi.org/10.1130/0091-7613(1999)027<0495:SIDDDO>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 J. A. Wolff, F. C. Ramos, J. P. Davidson; Sr isotope disequilibrium during differentiation of the Bandelier Tuff: Constraints on the crystallization of a large rhyolitic magma chamber. Geology 1999;; 27 (6): 495–498. doi: https://doi.org/10.1130/0091-7613(1999)027<0495:SIDDDO>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 1.61 Ma Otowi Member of the Bandelier Tuff (Jemez Mountains volcanic field, New Mexico) is a caldera-forming high-silica rhyolitic ignimbrite with a precursor fallout deposit. The Otowi Member has high Rb/Sr ratios; the 87Rb/86Sr ratios from sanidines and glasses range from 14 to 570. Most sanidines from glomerocrysts in the ignimbrite have 87Sr/86SrI = 0.7052–0.7056, whereas the ratios from glasses from glomerocrysts range from 0.7052 to 0.7079. Quartz phenocrysts containing glass inclusions from both the initial fallout and the ignimbrite are markedly more radiogenic, at 87Sr/86SrI = 0.7105–0.7113, despite having much lower Rb/Sr ratios than glomerocryst glasses. These relations require that the inclusion glasses are more contaminated with Proterozoic country rock than are glomerocryst glasses. Textural, isotopic, and trace element data support a model in which crystals grow in a boundary layer with the most inclusion-rich quartz grains closest to the magma–country rock contact. Phenocrysts and glomerocrysts represent fragments from different zones of the chamber's crystalline carapace, disseminated throughout the magma prior to eruption. An important implication of these results is that glass inclusions do not necessarily represent precursor magma compositions; hence extrapolation of measured volatile contents of inclusion glasses to the entire volume of an erupted magma should be approached with caution. 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.