Boron isotopic composition of subduction-zone metamorphic rocks

Simon M. Peacock, Richard Hervig

Research output: Contribution to journalArticle

145 Scopus citations

Abstract

Many arc lavas contain material derived from subducted oceanic crust and sediments, but it remains unresolved whether this distinctive geochemical signature is transferred from the subducting slab by aqueous fluids, silicate melts, or both. Boron isotopic measurements have the potential to distinguish between slab transfer mechanisms because 11B fractionates preferentially into aqueous fluids whereas little fractionation may occur during partial melting. Previous studies have shown that δ11B values of island arc lavas (-6 to +7) overlap the range of δ11B values for altered oceanic crust (-5 to +25) and pelagic sediments and turbidites (-7 to +11). Secondary ion mass spectrometry (SIMS) analyses of minerals in subduction-zone metamorphic rocks yield δ11B = -11 to -3 suggesting that slab dehydration reactions significantly lower the δ11B values of subducted oceanic crust and sediments. In order to explain the higher δ11B values reported for arc lavas as compared to subduction-zone metamorphic rocks, the B-bearing component derived from the metamorphosed slab must be enriched in 11B relative to the slab, favoring an aqueous fluid as the slab transfer mechanism.

Original languageEnglish (US)
Pages (from-to)281-290
Number of pages10
JournalChemical Geology
Volume160
Issue number4
DOIs
StatePublished - Sep 2 1999

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Keywords

  • Boron isotopes
  • Metamorphism
  • Subduction

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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