Molybdenum isotopes in hydrothermal manganese crust from the Ryukyu arc system: Implications for the source of molybdenum

Kosuke T. Goto, Gen Shimoda, Ariel Anbar, Gwyneth Gordon, Yumiko Harigane, Ryoko Senda, Katsuhiko Suzuki

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

A high concentration of molybdenum (Mo) is a striking feature of modern marine hydrothermal manganese (Mn) crusts from both low- and high-temperature hydrothermal systems; however, the origin of that Mo is poorly constrained. In this study, we analyzed Mo isotopic composition (δ<sup>98/95</sup>Mo) in a Mn crust collected from the Ryukyu arc system, and assessed the possible use of δ<sup>98/95</sup>Mo to constrain the origin of Mo in hydrothermal Mn crusts. Along with Mo isotope analysis, we also measured the abundance of major and trace elements and the Re-Os isotopic composition. The Mn crust sample had a high Mn content (42%-47%) and was low in Fe (0.2%-0.5%). Among the manganophile elements (Co, Ni, Cu, Zn, and Mo), only Mo showed high concentrations (>550ppm). We also found low contents of Os (~35ppt) with an isotopic composition of <sup>187</sup>Os/<sup>188</sup>Os=~1.00. These results are consistent with previously reported chemical compositions of hydrothermal Mn crusts. δ<sup>98/95</sup>Mo values in the sample ranged from -0.56‰ to -0.66‰, which are ~2.7‰ lighter than the present-day seawater δ<sup>98/95</sup>Mo but similar to those in modern hydrogenous Fe-Mn crusts and Mn nodules. Although current data do not preclude the possible contribution of hydrothermally derived Mo, the light δ<sup>98/95</sup>Mo values can be explained by isotope fractionation associated with a change in coordination number during the adsorption of Mo from seawater onto Mn oxides. We suggest that the δ<sup>98/95</sup>Mo data are useful for constraining the source of Mo in hydrothermal Mn crusts.

Original languageEnglish (US)
Pages (from-to)91-99
Number of pages9
JournalMarine Geology
Volume369
DOIs
StatePublished - Nov 1 2015

Keywords

  • Hydrothermal manganese crust
  • Manganophile element
  • Molybdenum isotope
  • Osmium isotope
  • Ryukyu arc system

ASJC Scopus subject areas

  • Oceanography
  • Geochemistry and Petrology
  • Geology

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