Abstract
The Cana Brava body is a 2.0 Ga, anorogenic, stratiform complex whose layers dip from 30º to 50º NW. The massif is made up of five units, composed of layers containing several associations of cumulus phases and variable amounts of inter-cumulus minerais. Transitions between units are characterized by changes in the composition and/or in the relative abundance of these phases. Stratigraphically, the lowest sequence is composed of amphibolites (PICB1), overlain by serpentinites (PICB2), metawebsterites (PICB3) and metagabbroic rocks (PICB4 and PICB5) at the top. This sequence was originally formed by microgabbros, peridotites, websterites and gabbroic rocks. The rock sequence of the complex can be attributed to a single magmatic fractionation. There is no evidence of multiple injections. Metamorphic events affected the different units heterogeneously. The gabbroic rocks (PICB4 and PICB5) were the least transformed; hence their chemical compositions are close to the original ones. Units PICB1 to PICB3 were the most affected by post-magmatic processes. Geochemical evidences suggest that PICB1 may be the chilled border of the massif. However, due to post-magmatic phenomena, the composition of the parent magma was calculated using the chemical compositions and inferred volumes of units PICB2 to PICB5. For PICB2 and PICB3 the compositions of mineral phases were utilized. The possible Cana Brava parent magma is olivine-tholeiite, similar to the majority of the complexes utilized for comparison. Its amount of normative olivine is within the range for liquids derived from 25 to 35% of mantle melting. Phase equilibria condictions point to pressures under 6-7 Kbar during crystallization. The possible parental magma of the Cana Brava complex is compared with the alcali-olivine basaltic magma of the Palmeirópolis metavolcano-sedimentary sequence, and with the possible parental magma of the Serra da Bota satellite body.
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