OLIVINE IN ANTARCTIC MICROMETEORITES - COMPARISON WITH OTHER EXTRATERRESTRIAL OLIVINE

Antarctic micrometeorite particles range from porous, unmelted samples to completely melted spheres. Of approximately 175 particles examined, twenty-six contain 5-mu-m or larger Mg-rich olivine with compositions similar to those found in unequilibrated meteorites. Electron probe analyses for minor elements show high levels of Cr in micrometeorite olivine above those found in C3 and UOC olivines but closely matching levels found in C2 olivines. Very Mg-rich (FeO < 1.0 wt%) olivines are rare in these micrometeorites but common in C2, C3, and UOC meteorites, suggesting that this component was not incorporated into micrometeorites. Likewise, olivines with high A1 and Ca are not present in these micrometeorites indicating an absence of the refractory enriched olivines found in C2, C3, and UOC meteorites. Olivine high in both Mn and Mg is not present in these micrometeorites but is present in C1 meteorites and interplanetary dust. The individual chemical features of olivines from the primitive samples indicate that each sample type has incorporated a particular compositional type of olivine rather than sampling a homogeneous olivine reservoir.