Textural features and olivine fabrics as petrogenetic indicators in the Niqualandia Complex of Central Goiás (Brasil)

The Niquelàndia Complex belongs to an alignment of mafic-ultramafic massifs situated in Central Goiás (Brasil). The Complex displays the following stratigraphy: a) a basal gabbroic zone (BGZ); b) a basal peridotite zone (BPZ); c) a layered ultramafic zone (LUZ); d) a layered gabbroic zone (LGZ). LUZ is a sequence formed by alternating peridotite and pyroxenite layers. The Complex has been interpreted in various ways. The most recent interpretations are those of Danni et al. (1982), who consider the Complex as a protoophiolitic suite, with presence of mantle peridotites (BPZ), and that of Rivalenti et al. (1982), who consider the Complex as a layered sequence formed by fractionation of a basic magma, without presence of mantle peridotites. Nevertheless, in both cases LUZ is considered as formed by fractionation and cumulus. The textural features do not constitute an unequivocal discrimination tool for the peridotites of the Complex, as foliated and cumulus textures occur both in BPZ and LUZ. The lack of discriminant textural features is stressed by fabric analysis. α-olivine fabric is usually weak and appears mainly related to the textural type rather than to the stratigraphic unit. The data presented in this paper suggest the idea that BPZ and LUZ rocks are kindred and formed by the same process.