Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

Tatsuhiko Kawamoto, Masami Kanzaki, Kenji Mibe, Kyoko N. Matsukage, Shigeaki Ono

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

Subduction-zone magmatism is triggered by the addition of H 2O-rich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical end-point. We ascertain critical endpoints between aqueous fluids and sediment or high-Mg andesite (HMA) melts located, respectively, at 83-km and 92-km depths by using an in situ observation technique. These depths are within the mantle wedge underlying volcanic fronts, which are formed 90 to 200 km above subducting slabs. These data suggest that sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, react with mantle peridotite to form HMA supercritical fluids. Such HMA supercritical fluids separate into aqueous fluids and HMA melts at 92 km depth during ascent. The aqueous fluids are fluxed into the asthenospheric mantle to form arc basalts, which are locally associated with HMAs in hot subduction zones. The separated HMA melts retain their composition in limited equilibrium with the surrounding mantle. Alternatively, they equilibrate with the surrounding mantle and change the major element chemistry to basaltic composition. However, trace element signatures of sediment-derived supercritical fluids remain more in the melt-derived magma than in the fluid-induced magma, which inherits only fluid-mobile elements from the sediment-derived supercritical fluids. Separation of slab-derived supercritical fluids into melts and aqueous fluids can elucidate the two slab-derived components observed in subduction zone magma chemistry.

Original languageEnglish
Pages (from-to)18695-18700
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number46
DOIs
Publication statusPublished - Nov 13 2012

Keywords

  • Adakite
  • Pelite
  • Second critical point
  • Synchrotron x-ray
  • Water

ASJC Scopus subject areas

  • General

Fingerprint Dive into the research topics of 'Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism'. Together they form a unique fingerprint.

  • Cite this