Magma plumbing systems in the Parnaíba Basin: Geochemistry, geochronology, and regional correlations with Mesozoic large igneous provinces

The Parnaíba basin is a 7.8 × 105 km2 Phanerozoic sedimentary province in NE South America which hosts basic and (rare) intermediate (to acid) rocks of large igneous provinces (LIP) related to the early stages of Atlantic rifting episodes. The Upper Triassic/Lower Jurassic (Rhaetian/Hettangian) Mosquito Formation of the Central Atlantic Magmatic Province (CAMP) has been historically characterized on the western side of the basin, while the Early Cretaceous (Hauterivian/Valanginian) Sardinha Formation of the Equatorial Atlantic Magmatic Province (EQUAMP) has been considered (supposedly) as the exclusive igneous manifestation on the eastern flank of the basin. We carried out an extensive sampling on the eastern border of the Parnaíba basin where were identified: (1) low-Ti tholeiites (LT) (TiO2 < 2 wt%) poor in incompatible elements (e.g., Sr < 245 ppm) with εNd from −1.08 to −1.71. These rocks yield 40Ar/39Ar age of 188.26 ± 1.52 Ma, interpreted as a disturbed age of a CAMP representative. Sharing geographical provinciality with LT a minor volume of (2) high-Ti tholeiites yielded a plagioclase 40Ar/39Ar date of 199.7 ± 1.6 Ma. This high-Ti Triassic group (HTt) has low P2O5 content (TiO2 2.0–2.5 wt%; P2O5 < 0.25 wt%), poor in incompatible elements content (Sr < 240 ppm) and it is highly radiogenic in Nd (εNd from 6.1 to 3.3). (3) Another prevalent group of high-Ti tholeiites (HT) (TiO2 > 2.4 wt%) is rich in incompatible elements (e.g., Sr > 400 ppm) and it is less radiogenic in Nd (εNd −2.17 to −3.04) being interpreted as a member of the EQUAMP. (4) Types with compositions chemically analogous to trachyandesite to trachytes (SiO2 > 56.5 wt%), here named as evolved rocks (ER), are interpreted as highly fractionated melts from EQUAMP HT tholeiites. The EQUAMP event was dated at 130.82 ± 0.24 Ma. Our new geochemical dataset composed of 111 samples, in combination with the previous databases of Atlantic-related LIPs in NE south America was qualitatively and (semi)automatically evaluated using the Self-Organized Maps (SOM) approach. The results shed light on the provinciality of tholeiitic magmatism in the Parnaíba basin, in association with correlated igneous events in the Borborema Province. The western Parnaíba basin volcanic (and intrusive) rocks belong to the CAMP event, while the eastern side is shared between CAMP and EQUAMP plumbing systems. Beyond the Parnaíba basin boundaries, low-Ti intrusions of the CAMP keep geochemical isotopic similarities with two ENE and NW-SE dike swarms of the Borborema Province, increasing its influence further east. High-Ti intrusions (Sardinha) retain high geochemical-isotopic-geochronological similarities with the Rio Ceará-Mirim and the Canindé giant dike swarms, thus endorsing the proposal of a single Cretaceous tholeiitic event related to the West Gondwana breakup.