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

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 (PArana ' Basin, Brasilia 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 Paran ' a 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 Paran ' a Basin, near the continental margin, comparatively thinner crust (similar to 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.

Automated summary

This study conducted a systematic wide-angle reflection and refraction seismic experiment for the crust and uppermost mantle in southeastern Brazil using controlled-source seismology. The obtained two-dimensional P-wave seismic velocity model revealed varying Moho depths (between approximately 31 and 45 km) and crustal thinning towards the continental margin. The modeled velocity structure provided new insights into the lithospheric morphology of the region, particularly within the lower crust and uppermost mantle. The findings suggested pervasive intrusion due to magmatic underplating in certain areas, while delamination may have caused thinner crust and lower velocity in the uppermost mantle near the continental margin.