An experimental study on kinetically-driven precipitation of calcium-magnesium-iron carbonates from solution: Implications for the low-temperature formation of carbonates in martian meteorite Allan Hills 84001

Spherical carbonate globules of similar composition, size, and radial Ca-, Mg-, and Fe-zonation to those in martian meteorite Allan Hills (ALH) 84001 were precipitated from Mg-rich, supersaturated solutions of Ca-Mg-Fe-CO2-H2 O at 150 OC. The supersaturated solutions (pH congruent to 6-7) were prepar ed at room temperature and contained in Teflon(TM)-lined stainless steel ve ssels, which were sealed and heated to 150 degrees C for 24 h. Experiments were also conducted at 25 degrees C and no globules comparable to those of ALH 84001 were precipitated. Instead, amorphous Fe-rich carbonates were for med after 24 h and Mg-Fe calcites formed after 96 h. These experiments sugg est a possible low-temperature inorganic origin for the carbonates in marti an meteorite ALH 84001.