South Atlantic Rift Segmentation From Demerara to Walvis: The Interplay Between Strike Slip Deformation and Rifting

Abstract

Rifting between South America and Africa started in the Late Jurassic-Early Cretaceous and eventually led to formation of the South Atlantic Ocean. Sea-floor spreading began in the Hauteruvian in the far south of the South Atlantic, with onset of spreading generally propagating northward, ultimately being fully developed in the equatorial South Atlantic in the Late Albian. Onset of rifting was however more complex with significant variations in the timing and local components of transtension and transpression, with timing being controlled by structural partitioning of the margins. We recognize five main structural segments, from Demerara-Guinea to north of the Walvis Ridge-Rio Grande Rise, based on geometries, space distribution and timing. These segments can be conveniently separated based on major fracture zones (FZ) in the oceanic crust. Segments from north to south are: 1) Dextral Equatorial Domain (Demerara to Charcot FZ), characterized by dextral strike slip rifting resulting in wrench tectonics and development of long offset transform margins and short oblique passive margins; 2) Benue-Pernambuco Plateau Orthogonal Domain (Charcot to Kribi FZs), in which pure extension evolved into normal passive margins; 3) The Northern Buffer Zone (Kribi to Bode Verde FZs), developed under sinistral transtension, that evolved inti oblique passive margins; 4) The Central compartment (Bode Verde to St Helena FZs) in which, like segment 2, pure extension evolved into normal passive margins; and 5) The Southern – Aptian Buffer Zone (St. Helena to Rio Grande Walvis FZs), similarly to segment 3, sinistral transtension evolved into oblique passive margins. Segments 1, 3, and 5 are large scale strike slip zones, segments 3 to 5 are sinistral while segment 1 is a dextral strike slip zone. An orthogonal zone (Segment 2) separated the right lateral from the left lateral segments. Segments 3 and 5 share the same characteristics of acting as a kinematic “Buffer Zone”. The term refers to a kind of relay zone accommodating differential extension between the neighboring segments. The Aptian Salt Basin is developed in segments 3 to 5. Therefore, we propose that presence of evaporites alone is not sufficient to describe those segments, and structural segmentation should be introduced to the description. Hydrocarbon exploration has been most successful in the sinistral domains, and even more so in segments 3 and 5.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018