The Romanche fracture zone influences the segmentation of the equatorial margin of Brazil

• Published in: Journal of South American earth sciences 2020-11, Vol.103, p.102738, Article 102738
• Main Authors: Tavares, Aline C., de Castro, David L., Bezerra, Francisco H.R., Oliveira, Diógenes C., Vannucchi, Paola, Iacopini, David, Jovane, Luigi, Vital, Helenice
• Format: Article
• Language: English
• Subjects: Equatorial Atlantic; Fracture zone; Hyperextended margin; Romanche; Transform margin
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2020.102738

This study addresses the crustal segmentation of the Brazilian equatorial margin (BEM) controlled by the Romanche fracture zone (RFZ). It uses a combination of satellite and marine gravity anomalies and seismic reflection data to constrain the continent-ocean crust transition. We propose a simplified evolution model of the BEM that involves dextral strike-slip plate motion along the RFZ in an oblique margin transform setting, which caused differential extension of a 31 km thick continental crust and the subsequent generation of a 5.0–10 km thick oceanic crust in the early Cretaceous. As a result, the trend of the coastline is controlled by two main directions: NW-SE and E-W. Two NW-SE-oriented segments, which are related to the oblique spreading centers, formed during the initial generation of oceanic crust adjacent to the margin. The western segment exhibits an ~160-km-wide hyperextended crust orthogonal to the shoreline, with a constant thickness of 10 km. In contrast, the eastern segment exhibits a 90-km-wide continental crust and a 13 km-thick oceanic crust. The central E-W-oriented segment is related to the RFZ and presents a sharp and steep boundary between the continental and oceanic crusts. The breakup geometry and shoreline orientations and the subsequent oceanic spreading centers are oblique (~40°) to the transform. In the Santonian (~83.5 ± 8 Ma), when the transform margin reached its passive stage, isochron 34 became orthogonal to the transform. At present, the RFZ forms well-defined ridges in the equatorial Atlantic that rise to ~2.5 km above the surrounding basins. These ridges and a series of NW-SE-oriented seamounts acted as a topographic barrier and prevented the deposition of a significant volume of sediment sourced from the continent. In addition, neotectonic reactivation of the fracture zone with a major normal component along the continental-oceanic lithospheric boundary (COB) indicates that the RFZ is a long-lived fault. •The Romanche fracture zone controlled the Brazilian equatorial margin evolution.•Geophysical data reveal a crustal segmentation of the Brazilian equatorial margin.•The western segment displays a broader hyperextended crust.•Dextral strike-slip movements along the RFZ characterize the central segment.•The eastern segment features a thicker oceanic crust intruded by seamounts.