Crystallization Experiments on a Gusev Basalt Composition

摘要: Introduction: Until recently, the SNC meteorites represented only source of information about igneous processes on Martian surface [1]. Many experiments have been conducted meteorite compositions to investigate their parental liquid compositions, and therefore provide mantle that produced such rocks. Recently, MER rover Spirit analyzed basalts Mars which may additional data mantle. The Adirondack-class by are dark, fine-grained vesicular rocks with <25% olivine pheoncrysts [2-4] suggested represent compositions. Experiments these can as whether derived melts or subsequent fractionation products. Liquidus crystallization determine not a rock is if there single pressure temperature at minerals crystallizing liquidus same composition those in was from. Therefore, order Adirondack class liquids, suite near-liquidus from 15.2 kbar 3.2 (1 atm on-going) one basalt (Humphrey). Humphrey chosen because it probably least altered [2]. Experimental technique: A synthetic powdered starting material made mixture oxides (Table 1). It subsequently fired 1400° C 1 ensure homogeneity well freedom water CO2. powder stored desiccator. After loading into graphite capsule, capsule were dried 350°C for 12 hours they remained volatile free. piston-cylinder apparatus using BaCO3 sleeves crushable MgO spacers 4 16 nominal. Pressures temperatures corrected negative 0.8 correction 10 degree correction. currently progress 1atmophere pressures above 15 kbar. Temperature measured W5Re/W25Re thermocouple. piston-out procedure (i.e. pressurized two experimental then brought down final after heating). Samples melted 30 minutes rapidly cooled where 1-4 (longer times lower temperatures). run products Cameca SX-100 electron microprobe NASA JSC major element abundances residual crystal phases. Mass balance calculations square computations IgPet [5] mineral no phase missed during analysis. Results: Figure shows relation diagram composition. below all liquidus; temperatures, pigeonite next crystallize. At kbar, still phase; however, once begins becomes dominant assemblage (Figure 2). This suggests higher be underway exact location, P-T space, phase. Table 1. Glass Gellert et al. [4] McSween [2] SiO2 45.99 46.96 46.49 TiO2 0.56 0.59