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Title: Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas

Abstract

The first measurement of {sup 18}O/{sup 16}O 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 and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} 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 lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetitemore » oxygen isotope temperatures are inconsistent.« less

Authors:
;  [1];  [2]
  1. (Univ. of Michigan, Ann Arbor (United States))
  2. (Indiana Univ., Bloomington (United States))
Publication Date:
OSTI Identifier:
7004210
Resource Type:
Journal Article
Journal Name:
Geology; (United States)
Additional Journal Information:
Journal Volume: 20:4; Journal ID: ISSN 0091-7613
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ALEUTIAN ISLANDS; GEOLOGIC FORMATIONS; ANDESITES; PETROGENESIS; ANORTHOSITES; CHEMICAL COMPOSITION; BASALT; PYROXENES; GEOCHEMISTRY; GEOLOGIC HISTORY; ISOTOPE RATIO; LAVA; OXYGEN ISOTOPES; CHEMISTRY; GABBROS; IGNEOUS ROCKS; ISLANDS; ISOTOPES; MINERALS; OXYGEN COMPOUNDS; PLUTONIC ROCKS; ROCKS; SILICATES; SILICON COMPOUNDS; VOLCANIC ROCKS; 580000* - Geosciences

Citation Formats

Singer, B.S., O'Neil, J.R., and Brophy, J.G. Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas. United States: N. p., 1992. Web. doi:10.1130/0091-7613(1992)020<0367:OICOTP>2.3.CO;2.
Singer, B.S., O'Neil, J.R., & Brophy, J.G. Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas. United States. doi:10.1130/0091-7613(1992)020<0367:OICOTP>2.3.CO;2.
Singer, B.S., O'Neil, J.R., and Brophy, J.G. Wed . "Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas". United States. doi:10.1130/0091-7613(1992)020<0367:OICOTP>2.3.CO;2.
@article{osti_7004210,
title = {Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas},
author = {Singer, B.S. and O'Neil, J.R. and Brophy, J.G.},
abstractNote = {The first measurement of {sup 18}O/{sup 16}O 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 and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} 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 lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent.},
doi = {10.1130/0091-7613(1992)020<0367:OICOTP>2.3.CO;2},
journal = {Geology; (United States)},
issn = {0091-7613},
number = ,
volume = 20:4,
place = {United States},
year = {1992},
month = {4}
}