Crystallization Experiments of Dar Al Gani Martian Meteoites: a Preliminary

Introduction: Recently, a lot of basaltic shergottites have been found from the desert areas in northern Africa and Middle East Asia. Most of them contain large olivine grains that are not present in the previously known basaltic shergottites (except for EETA79001). These olivine grains are mostly Mg-rich, but they show different mineralogical features in each meteorite. Dar al Gani 476 and its paired samples are mainly composed of olivine, pyroxene and plagioclase (now transformed into “maskelynite”). Olivine is present as a megacryst, and its core is too Mg-poor to be in equilibrium with its bulk composition. Pyroxene in Dar al Ganis are more Mg-rich than those of the other basaltic shergottites, and rather similar to those in lherzolitic shergottites [1,2]. Therefore, Dar al Ganis are believed to offer significant information on the relationship between lherzolitic shergottites and basaltic shergottites or other martian meteorites. Oxygen fugacity under which Dar al Gani crystallized was estimated about QFM-2.3 [3]. In this abstract, we present the initial results of our ongoing crystallization experiments on the bulk composition of Dar al Gani shergottites to advance understanding of the formation of these meteorites. Experiments: The starting composition having the average bulk compositions of Dar al Gani 476 and 489 [4,5] were prepared (Table 1). Na and P are lower than those of the bulk Dar al Ganis because of the problem on the process of making the glass, but both elements hardly affect mineral crystallization except late-stage minerals. Pellets of the starting material were suspended in vertical furnaces at 1450C for 48 hours for homogenization, and then quenched to room temperature. Glass charges were put back into the furnace and held for another 48 hours at the target temperature, then quenched in air and analyzed by electron microprobe. The oxygen fugacity was controlled at IW+1.5 by gas mixture of H2-CO2. Table 2. Phase assemblage of the crystallization experiments.