Petrogenesis of the Low-TiO2 Batalha Suite in the eastern Parnaíba basin, northeastern Brazil
In the Parnaíba basin, northeastern Brazil, some records of basic tholeiitic magmatism have been recognized as part of large igneous provinces (LIP’s). They are represented by the Mosquito basaltic flows (Triassic–Jurassic; ca. 200 Ma) that occurs in the west portion of the basin as well as the Sardinha diabases (Cretaceous; ca. 124 Ma) eastwards. The Mosquito and Sardinha magmatic rocks of the Parnaíba basin were related to the processes of distension and rupture of Pangea and Gondwana, respectively. This paper presents the petrogenesis of diabase sills that occur in the eastern portion of the basin, probably associated with the Sardinha formation. The studied rocks are mostly equigranular, medium-grained diabases. They are tholeiitic andesite-basalts and stricto sensu basalts, comprising a single Low-TiO2 (TiO2 < 2 wt%) magmatic suite here denominated as Batalha Suite. They show relative enrichment in the broad spectrum of LILE (large ion lithophile elements), HFSE (high field strength elements) and REE (rare earth elements) when compared to MORB, chondrite and primitive mantle, similar to continental flood basalts (CFB) elsewhere. This suite evolved by fractional crystallization as attested by whole-rock geochemistry, mineral chemistry, geochemical modeling and Sr–Nd isotope data. The studied Low-TiO2 basalts derived from an enriched mantle source likely to be represented by the subcontinental lithospheric mantle (SCLM). The diabases are related with 16% of partial melting of either a less enriched residual garnet harzburgitic source or a more enriched residual spinel-harzburgite.