Crustal structure of the eastern Borborema Province, NE Brazil, from the joint inversion of receiver functions and surface wave dispersion: Implications for plateau uplift

Abstract

AbstractWe investigate the crustal structure of the Borborema Province of NE Brazil by developing 44 S wave velocity‐depth profiles from the joint inversion of receiver functions and fundamental mode, Rayleigh wave group velocities. The Borborema Province is located in the northeasternmost corner of the South American continent and represents a portion of a larger Neoproterozoic mobile belt that formed during the Brasiliano‐Pan African orogeny. Extensional processes in the Mesozoic—eventually leading to the separation of Africa and South America—left a number of aborted rift basins in the continental interiors, and episodes of diffuse intraplate volcanism and uplift marked the evolution of the Province after continental breakup. Our velocity‐depth profiles reveal the existence of two crustal types in the Province: (i) the thin crustal type, which consists of 30–32.5 km thick crust, with an upper layer of 3.4–3.6 km/s overlying a lower layer of 3.7–3.8 km/s and (ii) the thick crustal type, which consists of a 35–37.5 km thick crust, with velocities between 3.5 and 3.9 km/s down to ∼30 km depth and a gradational increase in velocity (VS≥4.0 km/s) down to upper mantle depths. The crustal types correlate well with topography, with the thick crustal type being mainly found in the high‐standing southern Borborema Plateau and the thin crustal type being mostly found in the low‐lying Sertaneja depression and coastal cuestas. Interestingly, the thin crustal type is also observed under the elevated topography of the northern Plateau. We argue that the thick crustal type is rheologically strong and not necessarily related to postbreakup mantle processes, as it is commonly believed. We propose that extensional processes in the Mesozoic stretched portions of the Brasiliano crust and formed the thin crustal type that is now observed in the regions of low‐lying topography, leaving the rheologically strong thick crust of the southern Plateau at higher elevations. The crust making the northern Plateau would have thinned and subsided during Mesozoic extension as part of a greater Sertaneja depression, to then experience uplift in the Cenozoic and achieve its present elevation.