EXPERIMENTAL CRYSTALLIZATION OF A FLUORINATED AND CHLORINATED PROPOSED ALKALIC PARENT TO THE CHASSIGNY MARTIAN METEORITE

The Chassigny Martian meteorite is a cumulate dunite with some cumulate chromite, interstitial pyroxene, and interstitial maskelynite. The cumulate olivines host polyphase melt inclusions, and the phases present within these polyphase melt inclusions parallel those produced during the experimental fractionation of a silica-saturated hawaiite at 10 kbar [Nekvasil et al., (2004) J. Petrol. V.45, 4.]. One major difference, however, between the Chassigny assemblages and those produced experimentally is the apparent abundance of Cr, F, and Cl as evidenced by abundant chromite and the presence of kaersutite, Ti-biotite, and F-Cl apatite in the meteorite. Could a similar hawaiite, but one with added Cr, F, and Cl produce more closely the mineral assemblages and glasses seen in the Chassigny olivine-hosted melt inclusions? If so, then these experiments could also be used to assess volatile partitioning between mineral and melt which can be used to assess volatile budgets in Martian magmas.

Piston-cylinder experiments are being conducted to assess the individual effects of F and Cl on the crystallization path of a silica-saturated hawaiite. Graphite capsules and BaCO₃ cells are being used in all experiments. Since previous work by Nekvasil et al. (2004) has indicated that an assemblage most similar to that of the chassignites is produced from hawaiite at pressures above 4.3 kbar and water contents above 0.4 wt%, experiments are being conducted here at 10 kbar (nominal).

Results indicate that the addition of 1 wt% Cr₂O₃ to the hawaiite produced chromite of the composition seen in the Chassigny melt inclusion spinel. The effect of F is quite different than the effect of similar amounts of water. Most notably, the F-bearing experiments produced liquids along a silica- and Na-depletion trend that does not lead to the rhyolite of the Chassigny melt inclusions. Similar experiments are being conducted for Cl-bearing hawaiite.