Tectono-magmatic evolution of the Walvis plateau: Multi-scale and polyphased interactions between mantle plume, rifting and transform activity

The Walvis transform marginal plateau constitutes a key geodynamic node in the evolution of the South Atlantic Ocean. It is the conjugate of the Santos transform marginal plateau. Both plateaus formed associated successively with: (1) the Austral South Atlantic rifting marking the separation of the southwestern Gondwana during the end of the Late Jurassic and Early Cretaceous with a northward propagating breakup between 133-124 Ma (M11 à M2). This stage was narrowly associated with the mantle plume of the Tristan Da Cunha Hot spot, at the origin of the Paranà-Etendeka Trapp (135-132 Ma). It is associated with the divergent opening of the North Pelotas magma-rich margin. (2) The later opening of the Central Atlantic segment (113 Ma) between Angola and Brazil. The Walvis and Santos plateaus separated during this stage along the Florianopolis Transform Zone in the Albian.

In this context, the Walvis Plateau probably marks a dynamic and persistent mantle-influenced complex. This system not only controlled the tectonic, volcanic, and topographic local processes, but also played a critical role as a rift propagation barrier toward the north, preserving a magmatic landbridge between continents, disturbing the establishment of the oceanic connection between the austral et central segments of the South Atlantic Ocean, and therefore the deep oceanic circulations. A detailed description of these multi-scale interactions is essential for understanding the links between regional dynamics, magmatism, and oceanic evolution at the start of the formation of the South Atlantic.

In this study, we propose a multi-sequential tectono-magmatic description of the Walvis Ridge. Through the interpretation of deep penetrating multi-channel seismic reflection profiles and wide-angle refraction lines, combined with magnetic and gravimetric anomalies, we describe the structuration of the Walvis Plateau. The analysis of these data enables us to identify and delineate several key aspects: major seismic/geologic units, crustal architecture, the structural genetic passive margin domains from Moho interface inflections, and the spatial-temporal sequencing of effusive magmatic events, called Seaward Dipping Reflectors (SDRs). Most of those SDRs evolve gradually from east to west. Between magnetic anomaly M4 and M0, a notable feature of this evolution is the appearance of a preserved proto-magmatic center, identifiable by a double verging structure, oriented N-S and turning E-W to the south, probably signing a magmatic reorganization at some stage. Within the overall relative westward motion of the effusive systems, we show that it gradually orients towards the north in the direction of the core of the Walvis Plateau together with the development of a large lava delta prograding southward. At a later stage, the plateau is affected by large normal faults forming a graben in the thinned domain, coevally to the formation of the Florianopolis Transform Fault.

This study highlights the complex interactions between tectonic and magmatic processes in a polyphased breakup and oceanisation setting, integrating the influence of the mantle plume and geological inheritance of Gondwana Supercontinent. It provides new perspectives on the Walvis Plateau dynamics and, more generally, on the formation and rupture of marginal magmatic transform plateaus.