The “3-Basins” Project in Mid South America and the Geometry of the Deep Nazca Subducted Slab

A multi-national two-year deployment of ~50 stations covering SW Brazil, Eastern Bolivia, Paraguay, NE Argentina and NW Uruguay will better map the crustal and upper mantle structure in this yet unexplored part of the South American plate. We aim at studying how deep structure and mantle convection controls the evolution of three intracratonic basins: Pantanal, Chaco-Paraná, and Paraná.

The Quaternary Pantanal Basin is especially interesting because of its present subsidence and possible influence from Andean flexural effects as well as from deep mantle convection associated with the Nazca slab . The Nazca slab has a flat segment, just above the 660-km discontinuity (beneath the Chaco Basin in Paraguay), and then plunges beneath the Pantanal Basin reaching about ~1000 km depth in SE Brazil (Schimmel et al., 2003; Rocha et al. 2011; Simmons et al., 2012). To the north of the Pantanal Basin, the Nazca slab seems to plunge directly through the transition zone without any deep flat segment. Initial studies of receiver functions from the transition zone were made using stations of the permanent Brazilian Seismic Network: the cold Nazca slab makes the 660-km discontinuity deeper between the Peru-Brazil border and the Pantanal basin, but does not affect the discontinuity depth beneath the Paraná basin further to the east.

It is expected that the newly deployed temporary stations will significantly improve the maping of the geometry of the Nazca slab within and below the upper mantle transition zone in South America. Work supported by FAPESP grant 2103/24215-6.