The petrogenesis of tholeiitic diabases in eastern Parnaíba Basin: evidence for geochemical heterogeneities in the subcontinental lithospheric mantle in NE Brazil

ABSTRACT: The sedimentary rocks within the Paleozoic Parnaiba basin in NE Brazil were intruded by voluminous tholeiitic diabase sills and covered by coeval basaltic flows. This paper presents lithogeochemical data of borehole samples obtained from wells located in the eastern portion of the Parnaiba basin. The diabases are subalkaline tholeiitc rocks comprising three high-TiO2 and three low-TiO2 suites that are unrelated by differentiation processes. Fractional crystallization of olivine and augite was the predominantly evolutionary processes within individual high- and low-TiO2 suites as depicted by trace element geochemical modelling, exception being made for one low-TiO2 suite that evolved by AFC. Parental compositions for both low- and high-TiO2 suites are related with variably enriched, spinel harzburgitic sources likely to represent the heterogeneous subcontinental lithospheric mantle underneath the sedimentary basin. The geochemical provinciality of the Parnaiba tholeiitic magmatism seems unrelated with the Transbrasiliano Lineament but may be due to lithospheric mantle amalgamation and remobilization occurred during previous tectonic events.