Noble gas signatures of abyssal gabbros and peridotites at an Indian Ocean core complex

• Hidenori Kumagai

  Deep‐Sea Research Department Japan Marine Science and Technology Center (JAMSTEC) 2‐15 Natsushim‐cho, Yokosuka, 237‐0061 Kanagawa Japan

• Henry J. B. Dick

  Woods Hole Oceanographic Institution Woods Hole Massachusetts 02543 USA

• Ichiro Kaneoka

  Earthquake Research Institute The University of Tokyo Tokyo 113‐0032 Japan

抄録

We report some of the first noble gas data for in situ lower oceanic crust and shallow mantle. From a suite of gabbros and peridotites recovered from the Atlantis Bank oceanic core complex on the Southwest Indian Ridge, we measured He, Ne, Ar, Kr and Xe concentrations as well as 3 He/ 4 He and 40 Ar/ 36 Ar ratios, there by documenting the noble gas content and signature of oceanic lithosphere. Except for a single ultramylonite, the gabbros have higher 3 He/ 4 He ratios than atmospheric. Three gabbros have MORB‐like bulk 3 He/ 4 He ratios higher than 6R A despite variable helium concentrations, as much as two to three orders of magnitude lower than in MORB glasses. One of these is mylonitized, demonstrating that magmatic helium can be retained despite intense high‐temperature crystal‐plastic deformation in the lower crust. Of the gabbros measured, green amphibole‐bearing samples show relatively high helium abundances. Peridotite noble gas concentrations measured in clinopyroxene separates are dominantly lower than gabbros. Specifically, He abundances are similar to or greater than gabbros with MORB‐like 3 He/ 4 He isotopic ratios. All the gabbros and peridotite clinopyroxenes show severely contaminated 40 Ar/ 36 Ar values up to 1300. Magmatic 40 Ar is enriched in the oxide‐olivine gabbro with the highest 40 Ar/ 36 Ar in the entire sample suit. These results suggest as an actual data that the recycling of the lower oceanic crust and shallow mantle should be considered in modeling mantle evolution at least for helium. Measured helium abundances, though lower than in basalt glasses, are greater than those in crystalline MORB. Even if entire upper crust retains primary magmatic signature, oceanic lower crust and lithospheric mantle may impact larger by recycling due to their large volumes.

収録刊行物

• Geochemistry, Geophysics, Geosystems

  Geochemistry, Geophysics, Geosystems 4 (12), 9107-, 2003-12

  American Geophysical Union (AGU)

キーワード

• Geochemistry and Petrology
• Geophysics

詳細情報

• CRID: 1360011144290462592
• NII論文ID: 30022964373
• DOI: 10.1029/2003gc000540
• ISSN: 15252027
• Web Site: https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F2003GC000540
• Web Site: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003GC000540
• データソース種別:
  • Crossref
  • CiNii Articles
  • KAKEN