| Abstract |
Chondrules are once-molten sub-millimeter silicate spherules, mostly consisting of olivine, pyroxene, plagioclase and glass, and are major constituents of chondritic meteorites. Chondrules formed in the solar protoplanetary disk, although their formation processes are not understood.
Recent in-situ oxygen isotope studies by SIMS revealed that most chondrules have internally homogeneous oxygen isotope ratios even though individual chondrules have diverse oxygen isotope ratios of -10‰ to +2‰ in Δ17O (=δ17O-0.52×δ18O). Furthermore, characteristic correlations are recognized between oxygen isotope ratios (Δ17O) and Mg# (molar ratio, 100×MgO/(MgO+FeO), of ferromagnesian silicates) among chondrules in individual chondrites. These indicate that chondrule-forming melt had (probably not completely but almost) equilibrated with the ambient gas via evaporation and re-condensation during chondrule formation.
We propose that characteristic Δ17O-Mg# trends were caused by variation of H2O (ice?) abundance in the chondrule-forming environment and that oxygen isotope ratios and Mg# of chondrules could be useful tool to investigate migration of chondrules in the solar protoplanetary disk. This talk will be given in Japanese. |
