Oceanic remnants in the mantle of the Parana Basin, Central South Atlantic: supporting the large-scale geochemical anomaly in the Northern Parana-Etendeka LIP

The Parana Basin is one of the larger continental Paleozoic basin in Central South America. Although several studies investigated the flooring mantle of the Parana Basin, mantle-scale oceanic relicts have not been interpreted by previous regional geophysical studies. For this work, we used the global-scale tomographic model of P-wave velocity perturbation UU-P07 for mapping slab-like anomalies, and qualitative gravity and magnetic anomalies for indicating orogenic trends. Positive P-wave anomalies were mapped along fifty-two profiles, and revealed slab-like anomalies (long and segmented tabular mantle bodies), and four top slab surfaces (S1, S2, S3 and S4). The biggest anomalous mantle body (top surface S1) is transversal to the central-southern Brasilia Belt trending, and therefore it can be directly linked to the Southern São Francisco craton. However, the other three slab-like tabular bodies cannot be linked to outcropping orogenic trends, due to the extensive and thick sedimentary cover of the Parana Basin. Southwestern São Francisco Craton, elongated bodies coincide with Brazilian/Pan-African island arc collisions (top surface S2), but other possible slabs (top surfaces S3 and S4) are underneath Paraná Basin. Positive anomalies in the residual geoid anomalies (XGM2019e_2159 model) and transformed total magnetic field (vertical integration) follow the possible accretionary trend formed by S2, S3 and S4. Although the assumptions about the origin of these slab-like anomalies need to be investigated further, all these observations have shown the high complexity of the upper mantle beneath Parana floods. Facing the geophysical anomalies, we realize that the mapped slab-like bodies are mostly located under the Central-Northern Parana Basin, where several studies interpreted the existence of remnants of Proterozoic subductions in the mantle. Previous geochemical analysis had linked the high-Ti domain in the Central-Northern Parana floods with the partial melting of oceanic subduction relics. Nonetheless, the abundance of other incompatible elements (e.g., P, F and B) in the early phase of Central-Northern basaltic floods can be inherited from subduction remnants in the mantle. The remarkable early enrichment contrasts with the primitive mantle affinity in tholeiitic magmas of the relative late northern floods of the Parana Basin, the southern floods of the Parana Basin, the Etendeka counterpart, and the continental margins. In agreement with the previous understanding of the chemical evolution, we consider that the early magmatic phase was highly influenced by subcontinental subduction relicts. On the other hand, the advancing lithospheric embrittlement, due to the Atlantic opening process, intensified the rise of primitive fluids. Therefore, geophysical observations support the hypothesis of the existence of oceanic remnants from oceanic closure southern São Francisco Craton, due to the Western Gondwana’s assembly. The location of highly preserved oceanic-like mantle bodies supports the occurrence of enriched magmas in the early magmatic phase of the Northern Parana-Etendeka LIP.