4:45 PM - 5:00 PM
[SGC50-10] Volatile components of apatite grains from pyroclastic flow deposits of Aso volcano
Keywords:apatite, volatile component, water
We analyzed volatile compositions of apatite grains and melt inclusions in plagioclase phenocrysts from pyroclastic flow deposits of Aso volcano with EPMA and nano-SIMS. We analyzed 4 samples, ryholitic and andesitic of Aso-3 and Aso-4. EPMA and nano-SIMS analysis revealed that F concentrations in apatite in each sample show large variations while Cl concentrations are constant, suggesting that F and OH substitute for each other in the X site. OH concentration in apatite of mafic sample was larger than that of silicic one.
We find that F and Cl in apatite and these in melt inclusion have no correlation, while OH in apatite and water in host magma, which is estimated from temperature, pressure, the composition of plagioclase, and so on (Kaneko et al., 2007), have a positive correlation.We also find that the amount of OH and that of CaO, P2O5 and MgO in apatite have positive correlations, therefore Ca, P, and Mg could affect on the behavior of F and/or OH. Additionally, Number of cations in M site (assuming oxygen number = 13) was 4.66-4.88, which is smaller than expected from stoichiometry, suggesting that other components, such as rare earth elements, would be present in M site.