Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas

Journal Article · Wed Apr 01 00:00:00 EST 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0367:OICOTP>2.3.CO;2· OSTI ID:7004210

Singer, B S; O'Neil, J R ^[1]; Brophy, J G ^[2]

---

1. Univ. of Michigan, Ann Arbor (United States)
2. Indiana Univ., Bloomington (United States)

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.

• OSTI ID: 7004210
• Journal Information: Geology; (United States), Vol. 20:4; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

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