Estudo geoquímico e petrológico dos diques máficos da Região de Candeias-Campo Belo-Santo Antônio do Amparo (MG), porção meridional do Craton São Francisco

Abstract

Four groups of mafic dykes, distinguished by their petrographic, geochemical and tectonic features and designated as A1 amphibolites, A2 amphibolites, Gabbronorites and Gabbros, intrude the Campo Belo Metamorphic Complex in southern Minas Gerais. The majority of the samples have tholeiitic affinities, but the A2 amphibolites and one gabbronorite plot in the calc-alkaline field, and some A1 amphibolites and gabbronorites fall at the boundary of the two fields. The parental magmas of the four groups display different degrees of evolution: gabbros (mg# 0.18 - 0.23), gabbronorites (mg# 0.33 - 0.35), A2 amphibolites (mg# 0.34 - 0.37) and A1 amphibolites (mg# 0.24 - 0.45). Incompatible trace-element patterns, when compared with those of garnet and spinel peridotite sources, show enrichment of the original magmas, which mainly affected the parental melt of the gabbroic suite. This feature is attributed to either an enriched mantle source or crustal contamination. Major and trace element geochemistry indicates that the four groups are unrelated. Comparison of the trace-element patterns of the studied dykes with swarms from Salvador (Sao Francisco Craton), Carajas (Amazon Craton) and Crixas-Goias (Archean Block of Goias) suggest formation in an intracratonic environment.