Experimental petrology of meteorites: Phosphorus and oxygen isotopes in olivine

Experiments have been conducted to investigate the exchange and behavior of phosphorus and oxygen isotopes in olivine of extraterrestrial materials. The first project concentrated on determining the conditions necessary for the formation of phosphoran olivine in pallasite meteorites. Results indicate that phosphoran olivine forms during rapid crystallization and not subsolidus diffusion. Phosphoran olivine does not persist if the system closely approaches equilibrium. Models proposing that pallasites represent samples of a core-mantle boundary of a differentiated asteroid are inconsistent with these results.;The second and third projects involved the exchange of oxygen isotopes in chondrules at nebular pressures and temperatures, first observing gas-melt exchange, then olivine-melt exchange. In the gas-melt exchange experiments, a low pressure flow of carbon monoxide gas was reacted with an olivine-normative melt to simulate exchange with a nebular gas in the early solar system. No isotopic exchange between carbon monoxide and olivine-rich melt was detected. However, the experiments did demonstrate for the first time, the kinetic evaporation of oxygen. It was proposed that water vapor was likely the major oxygen-bearing species to exchange oxygen in the early solar nebula and carbon monoxide contributed to this only through reactions with the water vapor or ambient hydrogen. The final experiments involved exchange of oxygen between relict chondrule olivine, their overgrowths, and the chondrule melt. It was determined that Fe-Mg diffusion can obscure relict grains during chondrule crystallization. However, the original oxygen isotopic composition of those grains will remain intact. Durations of weeks at high temperature are required to obscure the oxygen signature by diffusion. Relict olivine grains are more prevalent than previously estimated and probably occur in more than 30% of all chondrules.