We present velocity anomalies for the upper mantle beneath the Pantanal, Paraná, and Chaco-Paraná basins, using teleseismic P-wave tomography. Three hundred thirty-nine stations were used to record 4,989 events for P and PKIKP phases, during the years 1992-2017. A new temporary deployment with 34 stations improved the coverage in that region. A high-velocity anomaly beneath the Paraná Basin was interpreted as a cratonic basement. Its northern portion is consistent with the cratonic block presented by Cordani et al. (1984), and the southern portion is consistent with that presented by Mantovani et al. (2005, https://doi.org/10.1016/s1342-937x(05)71137-0). Low velocities are consistent with the limits of the Rio de la Plata craton, proposed by Rapela et al. (2011, https://doi.org/10.1016/j.gr.2011.05.001). A low-velocity anomaly under the Pantanal Basin correlates with the seismicity, suggesting lithospheric thinning. This result is not consistent with an extension of the Rio Apa Block beneath the Pantanal Basin. We observed high velocities separating the Pantanal and South-Paraguay seismic zones. The Western Paraná Suture (as proposed by Dragone et al., 2017, https://doi.org/10.1016/j.precamres.2017.01.029) shows no correlation with the seismic tomography anomalies. The thick lithosphere in the central part of the Paraná Basin is consistent with deviation of mantle flow, as suggested by SKS fast polarization (Melo & Assumpção, 2018, https://doi.org/10.1093/gji/ggy288). Synthetic tests show low resolution of the model for structures smaller than 200 x 200 km in the southwest portion of the study area but good resolution for large structures. the Transbrasiliano Lineament (TBL; Figure 1): The Amazonian Domain, including mainly the Amazonian Craton and related to the supercontinent of Laurentia, and the Extra-Amazonian (or Brasiliano) Domain, related to the supercontinent of West Gondwana. The Brasiliano Domain was formed by several paleocontinental fragments, where the largest are the São Francisco and Rio de La Plata (RDLP) cratons and the Paranapanema Block.The understanding of the tectonic evolution of the SAP requires a study of how these various paleocontinental fragments are related and how this mosaic of fragments reached its present state. This is more important for the Extra-Amazonian Domain, where these fragments are smaller than for the main representative of the Amazonian Domain, the Amazonian Craton. Defining the limits and geometry of these fragments at depth using seismic tomography is one way to understand the processes that allowed the formation of the SAP, especially when those limits are covered by sedimentary basins, hindering direct geological observations. Several geological and geophysical studies have been conducted to better understand the layout and geometry of the various cratonic nuclei of the SAP. Cordani et al. (1984), based on regional geology and radiometric dating from deep boreholes, suggested the first limits of the cratonic block related to the Paraná Basin basement. Mantovani et ...

We present a new P‐wave seismic tomographic model for the region of the Paraná Basin and surroundings using a multiple‐frequency approach, providing better resolution than previous regional studies. We processed a total of 62,692 cross‐correlation delays for P, PKIKP, PcP, and PP phases distributed among 1,081 events using six different central frequencies (0.03, 0.06, 0.13, 0.25, 0.50, and 1 Hz). We merged our data with a previous multiple‐frequency study of the Amazonian Craton to cover regions outside of the study area, obtaining a total of 75,187 cross‐correlation delays. The data used are from the stations of the Brazilian Seismographic Network, and mainly from a temporary network (XC network) installed exclusively to study the region. The basement of the Paraná Basin is represented as a NE‐SW trending P‐wave high‐velocity anomaly, extending from the northern limit of the basin to the southwestern border of Brazil, consistent with previous reports. The limit between this block and the São Francisco Craton is characterized by decreased amplitude of the P‐wave high‐velocity anomaly. Synthetic tests show that a narrow boundary between these two blocks displays the same behavior. At the southeastern portion of this anomaly, decreasing amplitude is consistent with the limit of the Luiz Alves Craton, which was also corroborated by synthetic tests. The northern portion of the Rio Apa Block agrees with a previous tomographic model, confirming that it does not extend under the Pantanal Basin, however, in our model this structure does not extend as far south.