Articles | Volume 7, issue 2
Solid Earth, 7, 529–548, 2016
Solid Earth, 7, 529–548, 2016

Research article 11 Apr 2016

Research article | 11 Apr 2016

Geophysical evidence of pre-sag rifting and post-rifting fault reactivation in the Parnaíba basin, Brazil

David Lopes de Castro1, Francisco Hilário Bezerra1, Reinhardt Adolfo Fuck2, and Roberta Mary Vidotti2 David Lopes de Castro et al.
  • 1Programa de Pós-Graduação em Geodinâmica e Geofísica, Universidade Federal do Rio Grande do Norte, Natal, 59078-970, Brazil
  • 2Instituto de Geociências, Universidade de Brasília, Campus Universitário, Brasília, 70910-900, Brazil

Abstract. This study investigated the rifting mechanism that preceded the prolonged subsidence of the Paleozoic Parnaíba basin in Brazil and shed light on the tectonic evolution of this large cratonic basin in the South American platform. From the analysis of aeromagnetic, aerogravity, seismic reflection and borehole data, we concluded the following: (1) large pseudo-gravity and gravity lows mimic graben structures but are associated with linear supracrustal strips in the basement. (2) Seismic data indicate that 120–200 km wide and up to 300 km long rift zones occur in other parts of the basins. These rift zones mark the early stage of the 3.5 km thick sag basin. (3) The rifting phase occurred in the early Paleozoic and had a subsidence rate of 47 m Myr−1. (4) This rifting phase was followed by a long period of sag basin subsidence at a rate of 9.5 m Myr−1 between the Silurian and the late Cretaceous, during which rift faults propagated and influenced deposition. These data interpretations support the following succession of events: (1) after the Brasiliano orogeny (740–580 Ma), brittle reactivation of ductile basement shear zones led to normal and dextral oblique-slip faulting concentrated along the Transbrasiliano Lineament, a continental-scale shear zone that marks the boundary between basement crustal blocks. (2) The post-orogenic tectonic brittle reactivation of the ductile basement shear zones led to normal faulting associated with dextral oblique-slip crustal extension. In the west, pure-shear extension induced the formation of rift zones that crosscut metamorphic foliations and shear zones within the Parnaíba block. (3) The rift faults experienced multiple reactivation phases. (4) Similar processes may have occurred in coeval basins in the Laurentia and Central African blocks of Gondwana.

Short summary
We combine new seismic data and well logs with airborne gravity and magnetic data to reveal the internal architecture of the Parnaíba basin. This Phanerozoic sedimentary basin overlies a large region of Precambrian crustal blocks in the South American platform before the break-up of the West Gondwana in Early Cretaceous. The tectonic evolution of this important cratonic basin involved a complex rifting phase followed by a long period of sag subsidence, with multiple fault reactivation.