LAUSR

Abstract The southern section of the Parana-Etendeka large igneous province exposes a sequence of heterogeneous Low-Ti lava packages that range compositionally from olivine tholeiites to rhyolites. The recent advances in the volcanic stratigraphy provide a high-resolution framework that constrains the spatial and temporal evolution of the lava sequence. The stratigraphy is formed by Low-Ti lavas, separated in four volcanic units, namely: Torres, Vale do Sol, Palmas and Esmeralda. Our data shows that individual volcanic units can be separated chemically and represent distinct batches of magma. The composition of erupted lavas is mostly controlled by a complex interplay between source composition and crystallization (±assimilation) within the crust. The magmatic plumbing system evolved gradually from the onset, towards the climax and waning phase of magmatism. LIP onset is composed by more primitive (MgO > 5%) pahoehoe basalt lava flows of the Torres Formation. These low-volume eruptions were fed by a poorly connected magmatic plumbing system focused within the lower crust. Geochemical evidence suggests that the parental basalts of Torres Formation were derived from picritic primary magmas that have evolved by fractional crystallization and assimilation of enriched lithospheric materials. The main phase of magmatism is formed by thick (>20 m), tabular, crystal-poor lavas with evolved composition, including the basaltic andesite of the Vale do Sol Formation and silicic rocks of the Palmas Formation. These large volume eruptions were formed by extensive fractional crystallization (+assimilation) of precursor basaltic magmas and directly fed by shallow magma chambers within the upper crust. The waning phase of magmatism, recorded in the Esmeralda Formation basalts-basaltic andesite, is marked by low-volume Hawaiian-like eruptions of compound lava flows at the surface and the retraction of the magmatic plumbing system at depth. These lavas also mark a shift towards more primitive (asthenospheric) compositions and the shallowing of mantle melting, reflecting the progressive extension of lithosphere during magmatism. For the Low-Ti lava sequence of the Parana-Etendeka, the surface expression and composition of lava fields are directly controlled by crystallization (+assimilation) processes, and these petrological processes can account for broad geochemical variations within large igneous provinces.