Joint inversion of receiver functions and surface-wave dispersion in the Pantanal Basin (Central South America): Constraining models of basin formation.

The origin and evolution of the Pantanal basin have been investigated through velocity-depth profiles developed from the joint inversion of receiver functions and surface-wave dispersion velocities at 33 broadband stations. The Pantanal basin is a shallow and wide depression in South-Central Brazil that developed within the Andean foreland in response to loads and flexural bending of the South American plate. Our results reveal the existence of up to four different crustal types that correlate with surface geology: (i) crust of 35 km with VS < 4.0 km/s, under the basin and along the SW projection of the Transbrasiliano lineament (TBL); (ii) crust of 45 km with VS > 4.0 km/s below 40 km depth, flanking the basin to the east and west; (iii) crust of 50-55 km with VS > 4.0 km/s below 40 km depth, flanking the basin to the north and south and along the TBL; and (iv) crust of 42.5-45.0 km with VS < 4.0 km/s in the neighboring Paraná basin. Existing geodynamic models propose that the Pantanal basin formed either in the back-bulge of the flexural system or at the top of the forebulge, due to extensional bending stresses that reactivated preexisting faults in the shallow upper crust. We argue that the Pantanal basin was formed in a structurally weaker portion of the foreland crust that was affected by delamination and enhanced bending of the South American plate. Our findings do not allow for discrimination among the competing models but suggest that the TBL was critical in marking the location, origin, and evolution of this basin.