Mafic subvolcanic intrusions from the southern Paraná‐Etendeka Large Igneous Province, Brazil: Insights from geochemistry and Sr–Nd–Pb isotopes

Abstract

The Early Cretaceous Paraná‐Etendeka Igneous Province is a predominantly tholeiitic sequence of continental flood basalts and silicic magmatism that is intimately associated with the rupture of the western Gondwana. Intrusions of tholeiitic compositions are very common within the province and represent the magmatic plumbing system that fed the lavas at the surface. The investigated dikes are in the southeast of the Paraná Basin, southermost Brazil. The Silica Saturated Olivine Tholeiite (SSOT) dikes show restricted isotopic ranges (87Sr/86Sri = 0.70570 to 0.70585; ɛNdi = −1.01 to −4.49; 206Pb/204Pb = 18.031), with no equivalent low‐Ti magma type in the Paraná Province, but are close to the isotopic ratios of low‐Ti magma types with MgO > 7 wt%, such as Nil Desperandum in the Etendeka Province. The Silica Supersaturated Tholeiite dikes show broader isotopic ranges (87Sr/86Sri = 0.70787 to 0.71336; ɛNdi = −2.51 to −8.65; 206Pb/204Pb = 18.578–19.049), similar to the Gramado magma‐type and Tafelberg magma‐type in the Paraná‐Etendeka Province. This variation may have occurred due to the contamination at the time of magma rise and extrusion. Isotopic modelling showed that the fractional crystallization process and crustal assimilation played an important role from the magma rise through the conduits to the extrusion of the lavas. For the most primitive SSOT dikes, fractional crystallization was the most important factor for the magma evolution. The behaviour of the trace elements revealed that the assimilation of crust rocks with both Palaeoproterozoic and Neoproterozoic ages can be considered.