Cretaceous magmatic underplating and delamination beneath continental SE Brazil and their tectonic implications: Evidence from the PABBRISE wide-angle reflection and refraction seismic profile

Abstract

Controlled-source seismology provides robust methods to obtain information on the velocity structure of the crust and uppermost mantle. We present the first systematic wide-angle reflection and refraction (WARR) seismic experiment for continental southeastern Brazil: the NW-SE-oriented and ca. 700 km-long PABBRISE (PAraná Basin, Brasília and RIbeira orogens Seismic Experiment) profile. Using ray tracing, we obtained a two-dimensional P-wave seismic velocity model of the crust and uppermost mantle. Our model shows that Moho depths vary between ca. 31 and 45 km, with crustal thinning towards the continental margin. The modeled velocity structure sheds new light on the present-day lithospheric morphology of the region, with the most striking features noted within the lower crust and uppermost mantle. We show that beneath the Paraná Basin, parts of the lower crust and uppermost mantle were pervasively intruded due to magmatic underplating. We modeled a ca. 200 km-long and 11 km-thick (maximum thickness), high-velocity (7.20–7.80 km/s) lower crustal (HVLC) body in this region. Outside the Paraná Basin, near the continental margin, comparatively thinner crust (∼31 km) with low mean P-wave velocity (6.20 km/s) and a low velocity (<7.90 km/s) uppermost mantle probably are the result of delamination. Magmatic underplating and delamination can be linked with the breakup of Pangea and the opening of the South Atlantic Ocean during the Cretaceous.