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-Woriented 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-SEoriented 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 longlived fault.
The Romanche fracture zone influences the segmentation of the equatorial margin of Brazil / Tavares, Aline C.; de Castro, David L.; Bezerra, Francisco H.R.; Oliveira, Diógenes C.; Vannucchi, Paola; Iacopini, David; Jovane, Luigi; Vital, Helenice. - In: JOURNAL OF SOUTH AMERICAN EARTH SCIENCES. - ISSN 0895-9811. - STAMPA. - 103:(2020), pp. 0-0. [10.1016/j.jsames.2020.102738]
The Romanche fracture zone influences the segmentation of the equatorial margin of Brazil
Vannucchi, PaolaMembro del Collaboration Group
;
2020
Abstract
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-Woriented 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-SEoriented 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 longlived fault.File | Dimensione | Formato | |
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