Characterization of the crust and uppermost mantle beneath the São Francisco Craton (Brazil) and adjacent areas from Rayleigh wave tomography

SUMMARY This study investigates the crustal and uppermost mantle architecture beneath the São Francisco Craton (SFC), which constitutes the core of the broader São Francisco Paleocontinent (SFP), and its surrounding tectonic provinces through Rayleigh wave tomography, integrating ambient-noise (periods of 6–50 s) and earthquake-derived (periods of 9–180 s) dispersion curves. 2-D phase and group velocity maps were regionalized using adaptive parametrization, with the resolution assessed from checkerboard tests. A pseudo-3-D shear-wave velocity (VS) model was generated down to 70 km depth, from which crustal thickness was also derived using the maximum velocity gradient method. Results at shallow depths (2–10 km) identify the Paraná, Parnaíba and Tucano–Jatobá basins as low-velocity anomalies, while the São Francisco Basin is not fully resolved because its reduced thickness falls below the model’s resolution limit, despite its broad surface extent. In the middle-to-lower crust (20–40 km) inside SFC, a low VS corridor characterizes the Paramirim Aulacogen, highlighting the role of inherited rift structures and subsequent thermal reworking within the cratonic interior. At greater depths (60–70 km), the Borborema Province exhibits low velocities that contrast with the high velocities of the stable SFC root. The Moho map derived from tomography indicates crustal thickening beneath the Paraná and Parnaíba basins and the Brasília Belt, in good agreement with receiver-function estimates. Overall, the VS anomalies and Moho geometry in the regions neighbouring the SFC reveal high-velocity corridors with relatively thin crust (32–36 km) extending across the Tocantins, Mantiqueira and Borborema provinces, and projecting northwestward beneath the Parnaíba Basin. These results demonstrate that the boundaries of the São Francisco Paleocontinent extend significantly beyond its exposed surface limits within the crust and uppermost mantle. These boundaries are clearly discernible mainly at lower crustal depths and likely reach the upper crust. Furthermore, marginal deformations are primarily restricted to shallower levels of the crust, suggesting the preservation of a mechanically strong and continuous cratonic foundation beneath the surrounding orogenic belts and intracratonic basins. The main exception occurs along the southwestern margin, where the absence of a clear seismic boundary between the SFP and the Paranapanema Block suggests deep lithospheric integration or a boundary too narrow to be resolved by the present station geometry.