Boron Isotope Systematics of Slab Fluids as Inferred from a Serpentinite Seamount, Mariana Forearc

Laurie D. Benton, Jeffrey G. Ryan, Fouad Tera

Research output: Contribution to journalArticlepeer-review

Abstract

Serpentinite clasts and muds erupted from Conical Seamount, Mariana forearc, show substantial enrichment in boron (B) and 11 B (δ 11 B up to +15‰) relative to mantle values. These elevated B isotope signatures result from chemical exchange with B-rich pore fluids that are upwelling through the seamount. If the trends of decreasing δ 11 B with slab depth shown by cross-arc magmatic suites in the Izu and Kurile arcs of the western Pacific are extended to shallow depths (∼25 km), they intersect the inferred δ 11 B of the slab-derived fluids (+13‰) at Conical Seamount. Simple mixtures of a B-rich fluid with a high δ 11 B and B-poor mantle with a low δ 11 B are insufficient to explain the combined forearc and arc data sets. The B isotope systematics of subduction-related rocks thus indicate that the fluids evolved from downgoing slabs are more enriched in 11 B than the slab materials from which they originate. Progressively lower δ 11 B in arc lavas erupted above deep slabs reflects both the progressive depletion of 11 B from the slab and progressively greater inputs of mantle-derived B. This suggests that the slab releases 11 B-enriched fluids from the shallowest levels to depths greater than 200 km.

Original languageAmerican English
JournalEarth and Planetary Science Letters
Volume187
DOIs
StatePublished - May 1 2001

Keywords

  • boron
  • Leg 125
  • isotope ratios
  • fore-arc basins
  • serpentine
  • subduction

Disciplines

  • Earth Sciences
  • Geology
  • Physical Sciences and Mathematics

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