부산대학교 도서관

Archean carbonate rocks hosting sulphide-sulphate (anhydrite) phases are found in association with high-grade metamorphic rocks in the Caraiba Complex (central Bahia State, Brazil). The S-bearing rocks appear in drill-core samples in association with a meta-sedimentary (marble, calc-silicate, metapelite) sequence. δ 18 O values (+12‰ SMOW) are similar to those found in other Precambrian carbonates. δ 13 C values range from −6.5 to −12‰ PBD. A model for anhydrite genesis is not obvious. Low Fe levels, isotopic data and lithologic affinities with Archean carbonate sequences suggest the possibility of an evaporitic origin. Evidence of decarboxylation reactions and local accumulations of graphite suggest the possibility of sulphide formation by sulphate reduction. In any case, the extensive rôle of Archean life systems in the Caraiba paleoenvironment is evident. [ABSTRACT FROM AUTHOR]