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Russian Geology and Geophysics

2005 year, number 9

WIDESPREAD LATE MESOPROTEROZOIC THOLEIITIC MAGMATISM OF THE SAO FRANCISCO CRATON (BRAZIL): PETROLOGY, GEOCHEMISTRY AND GEOTECTONIC SETTINGS

A. De Min, A. Rosset, L.S. Marques*, A. Chaves**, and E.M. Piccirillo
Dipartimento di Scienze della Terra, University of Trieste (Italy),
Via Weiss, 8, palazzina N, 34127, Trieste, Italy
* Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, University of Sao Paulo (USP; Brazil)
** Instituto de Geociencias, University of Sao Paulo (USP; Brazil)
Keywords: Sao Francisco Craton, Mesoproterozoic, dyke swarms, tholeiites, genesis, Rodinia break-up
Pages: 966-978

Abstract

Several Late Mesoproterozoic (0.9-1.1 Ga) tholeiitic dyke swarms crop out along the eastern border of the Sao Francisco Craton (SFC, Brazil), inside the Neoproterozoic Aracuai mobile belt (Diamantina and Conceicao do Mato Dentro) and in Archean-Paleoproterozoic terrains (Belo Horizonte, Olivenca-Itabuna and Salvador). These last dykes were virtually unaffected by the Brasilian metamorphic events and show well-preserved magmatic textures and phases.
All the dykes are characterized by high (>2 wt%) and low (<2 wt%) TiO2 contents and show similar major element compositions, while important differences concern incompatible element contents and ratios. The southern SFC dykes (Diamantina, Conceicao do Mato Dentro and Belo Horizonte) show Nb/Y and Zr/Y ratios up to ~6 times higher than the northern ones (Olivenca-Itabuna and Salvador) implying variable residual source garnet and then heterogeneous mantle sources, due to the tholeiitic nature of these dykes. Furthermore, geochemical features as La/Nb in the ~0.7-1.9 range and Sr-Nd isotopic compositions recall both OIB (