A stepped combustion technique has been developed to resolve the different sulphur-bearing components of meteorites. The technique has been applied to studies of carbonaceous and enstatite chondrites.
Stepped combustion of C1 and C2 carbonaceous chondrites provides evidence for the presence of secondary sulphur minerals. Evidence for six different sulphur components has been found (elemental and organic sulphur, sulphides, FESON and sulphates). Most of the sulphur in C1 and C2 chondrites both contain the same sulphur components suggesting that hydrothermal alteration may have evolved along a common pathway. Changes in sulphur isotopic composition associated with alteration have led to an enrichment of 34S in elemental sulphur and sulphates compared to the starting sulphide material.
Most of the sulphur in C3, C4 and C5/6 chondrites is present as sulphide, but stepped combustion has demonstrated that there is also a component of preterrestrial oxidised sulphur in these materials. Chemical evidence suggests that oxidised sulphur may occur as FESON or anhydrite. This finding indicates that C3 and C4 chondrites have undergone a small amount of hydrous alteration on the meteorite parent body and this provides an important evolutionary link with C1 and C2 meteorites.
The stepped combustion method has been used as a means of assessing the relative abundances of the two main sulphides (troilite and oldhamite) in enstatite chondrites and aubrites. It was found that troilite and oldhamite abundances both decrease systematically with petrologic grade. The variability of these two minerals provides constraints on models envisaged for the evolution of the enstatite chrondrite parent body. Enstatite chondrites have whole-rock delta34S values of close to 0%, whereas aubrites are depleted in 32S by up to 2%
