Lithospheric structure of the western Borborema Province from receiver functions and surface-wave dispersion: Implications for basin inversion

The Proterozoic Borborema province of NE Brazil was under extensional stresses during the Mesozoic, causing stretching and thinning of the lithosphere. During Cenozoic times, compression associated with the development of the South Atlantic and collision along the Andean front dominated throughout the Province. One of the main consequences of such compression might have been the formation of the Chapada de Araripe, an inverted rift basin located in the Western Province. We undertook a passive seismic experiment along a NS profile crossing the Borborema province and a short EW profile across the Chapada de Araripe, with the goal of providing constraints on the origin of the Chapada de Araripe. A variety of mechanisms can contribute to basin uplift, so understinding basin inversion is in turn important for understanding the tectonic evolution and geodynamics of NE Brazil. Through joint inversion of receiver functions and surface-wave dispersion, we show that the crust is typically 34-38 km thick under the western Province; in contrast, the crust is 43-46 km thick under the northern craton. No apparent crustal thinning is observed under the Araripe Basin, due to the presence of a relatively thick (10-14 km) high-velocity (4.1-4.3 km/s) lowermost crust. Our velocity models also image a drop in S-velocity (from 4.6 km/s to 4.3 km/s) at 135-145 km depth under the southern half of the profile, which we interpret as a mid-lithospheric discontinuity, and at 120-140 km depth under the Araripe Basin, likely representing the lithosphere-asthenosphere boundary. Our findings confirm the presence of thin lithosphere under the Araripe Basin - originally postulated by a collocated MT survey - that might have facilitated tectonic inversion of this basin through regional stress concentration and thermal buoyancy. These findings also suggest additional buoyancy contributed by a mafic lowermost crust right under the basin.