Anomalously High δD values in an archean ferropicritic melt : implications for magma degassing

[Truncated abstract] In situ H isotope analysis of igneous amphibole from the Boston Creek ferropicrite, in the Abitibi Belt, Ontario, a 100-m-thick layered mafic-ultramafic unit, provides insights into the evolution of Archean mantle-derived hydrous melts in the crust. Ion-microprobe analyses of the ultramafic-rock-hosted interstitial igneous magnesiohastingsite indicate a wide range of δD values, from −47 to +54‰ and 2–3 wt% H2O at the 100–1000 μm intragrain scale, but relatively uniform major-element and incompatible trace-element compositions. This wide range encompasses values significantly higher than the δD values of −50‰ for whole-rock samples,