On the origin of incompatible element enrichment in the Venda Nova pluton, State of Espı́rito Santo, southeast Brazil

Abstract

The Venda Nova pluton, central portion of the Brasiliano Coastal mobile belt, southern region of the State of Espı́rito Santo, SE Brazil, is part of a late- to post-collisional magmatic arc, formed at the end of the Pan-African–Brasiliano orogeny. These rocks form a high-K calc-alkalic suite, including gabbro-norites, monzodiorites and syeno-monzonites. Minor granitic bodies at the border zone of the pluton are probably related to melting of paragneisses during igneous emplacement, as demonstrated by their geochemistry. Concentrations of Ba, Sr and LREE in the syeno-monzonites, monzodiorites and gabbro-norites are higher than those found in ocean island basalts (OIB) and might be attributed to direct or indirect crustal contamination. Primitive-mantle normalised spidergrams indicate Rb and K depletion in the more basic rocks, and HFSE and HREE depletion for all rocks. Such geochemical signatures are also observed for many other similar igneous rocks and basic occurrences in the Brasiliano Coastal mobile belt. Ba, Sr and LREE contents of granites and regional gneisses are lower than in the Venda Nova complex and together with other geochemical characteristics cannot be regarded as the source for the enrichment in these elements observed in the Venda Nova pluton. It is suggested that the source for the Venda Nova pluton as well as for other similar plutons and basic rocks from this region, was an enriched primitive mantle. Long-lived mantle anomalies in the region have been identified by a number of studies of Phanerozoic volcanic rocks.