The western São Francisco pericraton interpreted from crustal magnetic and gravity sources

Abstract

The Neoproterozoic Brasiliano Orogeny shaped the former São Francisco paleocontinent into a preserved cratonic nucleus surrounded by a pericratonic region. In central Brazil, this pericraton crops out as the Goiás Massif, the basement of the northern Brasília Belt. The well-known difficulty of tracing suture zones on surface led to a longstanding dispute on whether the Rio Maranhão Thrust, a structure separating the Internal Zone and the External Zone of the Brasília Belt, marked the Brasiliano suture. This interpretation was largely based on regional gravimetric data showing a steep discontinuity at depth, between these zones. However, the Rio Maranhão Thrust separates two pericratonic domains of the Goiás Massif (Campinorte Domain and Cavalcante-Arraias Domain), which otherwise share similar Paleoproterozoic ages and geology. To properly address the main structural boundaries within the northern Brasília Belt, this work was focused on comparing shallow and deep gravity and magnetic data processed as enhanced anomalies and through matched filter analysis. Our results show that the large mafic-ultramafic complexes within the Internal Zone of the Brasília Belt are masking a smooth gravimetric transition into the External Zone. Additionally, the alleged suture zone is coincident with the Mesoproterozoic rift-related Juscelândia and Palmeirópolis volcano-sedimentary sequences, which have been largely ignored in their role as creating magnetic and gravity suture-like signatures. Along with previous structural and geochronological data, our results argue against the Rio Maranhão Thrust as a suture zone and, instead, support the alternative interpretation of the thrust as an intracontinental feature within a portion of the São Francisco pericraton. This pericratonic region, unliked the preserved cratonic core, was widely affected by Mesoproterozoic rifting and Neoproterozoic thick-skinned thrusting. The Rio Paranã Thrust, on the other hand, is unnoticeable below 8 km depth in gravity and magnetic data, suggesting thin-skinned tectonics also associated with the Brasiliano Orogeny. Finally, the relative crustal homogeneity from the São Francisco craton into the Goiás Massif evidenced by our gravity data and confirmed by first- and second-order magnetic lineaments confirms the nature of a pericraton with dominantly NE (N20-40E) trending lineaments. These lineaments were progressively overprinted by Brasiliano NNE (N45-70E) structures from the western margin of the External Zone into the Internal Zone.