Research Article| April 01, 1992 Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas Bradley S. Singer; Bradley S. Singer 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Search for other works by this author on: GSW Google Scholar James R. O'Neil; James R. O'Neil 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Search for other works by this author on: GSW Google Scholar James G. Brophy James G. Brophy 2Department of Geology, Indiana University, Bloomington, Indiana 47405 Search for other works by this author on: GSW Google Scholar Author and Article Information Bradley S. Singer 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 James R. O'Neil 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 James G. Brophy 2Department of Geology, Indiana University, Bloomington, Indiana 47405 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1992) 20 (4): 367–370. https://doi.org/10.1130/0091-7613(1992)020<0367:OICOTP>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 Bradley S. Singer, James R. O'Neil, James G. Brophy; Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas. Geology 1992;; 20 (4): 367–370. doi: https://doi.org/10.1130/0091-7613(1992)020<0367:OICOTP>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 first measurement of 18O/16O ratios of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts from modern Aleutian island-arc lavas provides new insight and independent constraints on magma sources and intracrustal processes. Basalts are heterogeneous on the scale of the entire arc (δ18Oplag = 5.5‰-6.7‰) and individual volcanic centers (ranges of 0.3‰ to 0.8‰). Combined with Sr isotope and trace element data, δ18Oplag values suggest a variable magma source characterized by differences in the mantle wedge or the subducted sediment component along the volcanic front. Seven tholeiitic basalt to rhyodacite (50%-71% SiO2) lavas from the Seguam volcanic center have nearly identical δ18Oplag values of 6.0‰ ±0.2‰, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1150 ±100 °C (basalt) and 950 ±100 °C (rhyodacite). In contrast, δ18Oplag values of 12 calc-alkalic basaltic andesites and andesites (53%-62% SiO2) from the smaller Kanaga volcanic center span a broader range of 5.9‰-6.6‰, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting δ18O values (6.0‰ and 6.5‰) occur in one andesite (δ18Oplag = 6.6‰), and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent. One andesite, however, yields concordant oxygen isotope temperatures of ∼850 ±100 °C, and a two-pyroxene temperature of 920 ±50 °C. Assimilation of isotopically heavy crustal wall rock and mixing off basaltic and andesitic magmas explains the variable and high δ18Oplag values and low eruptive temperature of the Kanaga andesites. 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.