Deep crustal architecture of the Parnaíba basin of NE Brazil from receiver function analysis: implications for basin subsidence

Abstract

Abstract We investigated the crustal architecture of the Parnaíba basin of NE Brazil by analysing receiver functions along a c. 600 km long transect crossing the central portion of the basin. The transect consisted of nine broadband stations interspaced at c. 70 km distance recording continuously for a period of 15 months, with the goal of improving our understanding of the origin and evolution of this large cratonic basin. Our results show that crustal thickness varies between 39 and 45 km along the transect, gradually thickening towards the depocentre, and that bulk V p / V s ratios vary between 1.70 and 1.78. The crust can be divided into a 2.0–3.5 km thick layer of low-velocity sediments, a 15–20 km thick upper crust (3.5 < V s < 3.6 km s −1 ) and a 18–22 km thick lower crust (3.7 < V s < 3.8 km s −1 ). Near the depocentre, where the crust is thickest, the bottom 10–12 km of the crust are characterized by fast S-velocities (4.0–4.2 km s −1 ). Our findings confirm that stretching of the lithosphere is minimal and compatible with flexural subsidence. However, loading from a thick, high-density layer of mafic intrusive rocks pervading the lower crust – as recently proposed for the basin – is found to be inconsistent with our bulk V p / V s ratios and lower crustal S-velocities. Flexural bending by a deeper load, perhaps related to deep mantle convection, seems more plausible.