Geochemical and Sr-Nd-Pb isotopic insight into the low-Ti basalts from southern Parana Igneous Province, Brazil: the role of crustal contamination

The south hinge of the Torres Syncline in southernmost Brazil hosts a volcanic succession of pahoehoe and rubbly Gramado-type lavas belonging to the similar to 132Ma Parana-Etendeka Igneous Province. We evaluate the geochemical and Sr-Nd-Pb isotopic variations using local-scale stratigraphy in order to discuss the petrogenesis of lava flows in a single magma type and to estimate the role of crustal contamination and the potential contaminants involved. The geochemical and isotopic variations along the lava pile are not systematic, implying that the magma chamber could have undergone successive replenishments of basaltic magma. The process of crustal assimilation explains the high and widespread initial Sr isotopic ratios at 0.707798-0.715751 and the very low epsilon(Nd) at -8.36 to -5.41, with associated Pb isotopic variations (18.42<Pb-206/Pb-204 < 18.86; 15.65<Pb-207/Pb-204< 15.71; 38.62<Pb-208/Pb-204<39.37). The magmatic evolution of the SCSH and LJ lava flows begins with the storage of mafic liquids during a short period in the shallow-level magma chamber, which allowed the magma ascent with composition of olivine basalts. The continuous fractional crystallization within the magma chamber coupled with variable assimilation degrees of distinct contaminants with Palaeoproterozoic and Neoproterozoic ages, in addition to significant contribution of magma recharge, led to magma ascent with basaltic andesite composition that displays at surface a simple pahoehoe morphology. The continuous magma recharge in the magma chamber coupled with higher assimilation degree allowed the formation of basaltic andesite lavas with more contaminated isotopic signatures that exhibit rubbly morphology at the surface. Differentiation process of liquids coupled with the highest assimilation degrees of distinct contaminants during longer time in a shallow-level magma chamber, which is distinct from that where SCSH and LJ magmas have been stored, led to the formation of andesites of the Morro da Cruz section that exhibit the most contaminated isotopic signatures.