Noble gases in pillow basalt glasses from the northern Mariana Trough back-arc basin |
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| Authors: | YASUO IKEDA KEISUKE NAGAO ROBERT J STERN MAKOTO YUASA & SALLY NEWMAN |
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| Institution: | Department of Earth Science, Hokkaido University of Education at Kushiro, Kushiro, Hokkaido 085, Japan,;Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682–01, Japan,;Center for Lithospheric Studies, University of Texas at Dallas, TX 75083–0688, USA,;Marine Geology Department, Geological Survey of Japan, Tsukuba, Ibaraki 305, Japan,;Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA |
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| Abstract: | Noble gas concentrations and isotopic compositions have been measured in eight samples of pillow basalt glasses collected from seven different localities along 250 km of the Mariana Trough spreading and rifting axis. The samples have uniform and mid-ocean ridge basalt (MORB)-like 3He/4He values of 9–12 × 10–6 (6.4–8.6 times atmospheric) despite large variations in 4He. Concentrations of the noble gases Ne, Ar, Kr, and Xe show much smaller variations between samples, but larger variations in isotopic compositions of Ne, Ar, and Xe. Excess radiogenic 21Ne is observed in some samples. 40Ar/36Ar varies widely (atmospheric to 1880). Kr is atmospheric in composition for all samples. Some samples show a clear excess 129Xe, which is a well-known MORB signature. Isotopic compositions of the heavier noble gases (Ar, Kr, and Xe) in some samples, however, show more atmospheric components. These data reflect the interaction of a MORB-like magma with an atmospheric component such as seawater or of a depleted mantle source with a water-rich component that was probably derived from the subducting slab. |
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| Keywords: | atmosphere back-arc basin basalt basalt glass Mariana Trough mixing MORB noble gas |
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