Phase Equilibria and Crystal-Chemistry of Some Calcic Amphiboles

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9628212 Jenkins Several projects are proposed to examine at the macroscopic and microscopic levels key issues dealing with the quantitative use of amphiboles as indicators of pressure, temperature and chemical history of their host geologic terrane. These include: (1) Basic characterization studies on ferro-actinolite in the system CaO-FeO-SiO2-H2O to determine whether or not there is substantial substitution of Fe+2 for Ca on the M(4) site and investigation of the extent of Al substitution into ferro-actinolite via the Fe-tschermaks substitution to test the influence of Fe+2 on the solubility of Al into amphibole. (2) An investigation of the importance of the bulk chemistry of the mineral assemblage (carbonate-bearing vs. non-carbonate-bearing) and of the amphibole itself (tremolite-pargasite join) in the production of chain-width defects or variable-composition amphibole precursors. (3) An investigation to determine the distribution of Al on the octahedral and tetrahedral sites of amphibole. Oxidation states will be determined via wet chemistry or M ssbauer spectroscopy and of crystal structure via x-ray Rietveld refinement. Direct analysis of the atomic structure will be done via HRTEM.