The Barro Alto complex, central Brazil, is a layered mafic–ultramafic intrusion, which was subjected to granulite facies metamorphism during the Neoproterozoic. Ultra‐high‐temperature conditions are recorded by parageneses that occur in some lenses of quartz‐bearing rock (metagranite, metapelite and impure quartzite). The peak paragenesis consists of spinel+quartz±cordierite±leucosome (recording the former presence of melt with quartz in excess), which is replaced by either orthopyroxene+sillimanite or garnet+sillimanite. Quartz+biotite±sillimanite±garnet symplectites are ubiquitous and indicate reactions between Fe–Mg phases and melt. Late kyanite porphyroblasts have overgrown these symplectites. The direct replacement of spinel+quartz±cordierite by orthopyroxene+sillimanite or garnet+sillimanite occurred around the [Sa] invariant point, which appears only in a petrogenetic grid with inverted topology. The topology inversion occurs at conditions of high oxygen fugacity or due to the presence of ZnO‐bearing spinel. Minimum peak conditions of ultra‐high‐temperature metamorphism were calculated as c. 980 °C and c. 7.9 kbar. The succession of observed mineral textures can be explained by a near‐isobaric cooling P–T path, with a cooling stage occurring between c. 980 and 750 °C.
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Moraes et al. (2000) studied this question.