Modeling aqueous alteration of CM carbonaceous chondrites

Results from an inorganic geochemical modeling study support a scenario in which low-temperature aqueous alteration of an anhydrous CM asteroidal pare nt body and melt water from H2O and CO2 ices produces the altered assemblag e observed in CM carbonaceous chondrites (chrysotile, greenalite, tochilini te, cronstedtite and minor calcite and magnetite). We consider a range of p ossible precursor mineral assemblages, varying with respect to the Fe-oxida tion state of the initial anhydrous phases. The aqueous solutions produced by this alteration are generally strongly basic and reducing and a large qu antity of H-2, and possible CH4, gas can be released during aqueous alterat ion.