| Popis: |
Hornblende megacrysts from basaltic flows in several locations have been studied by means of the electron microprobe, Mossbauer spectroscopy, uranium extraction techniques, and mass spectrometry to define the interrelations between the concentrations of Fe 3+ and H + , and the hydrogen isotope partitioning (D/H) in mantle amphiboles. Results indicate a nearly perfect inverse relation between Fe 3+ content and H + content; no relation is observed between D/H partitioning and wt% H 2 O. A review of diffusion data for amphiboles suggests that the observed increase in Fe 3+ content with decreasing H + content may represent partial dehydration of the amphiboles during ascent. Thus, Fe 3+ and H + contents measured on amphiboles at Earth9s surface may not represent mantle conditions. Instead, high Fe 3+ contents may be indicative of high H + contents in the mantle source region rather than high mantle oxygen fugacities. |
