The Afar Triangle: A Key to Understanding the Tectono-Sedimentary Evolution of the Santos Basin/São Paulo Plateau

Event - AAPG ICE 2026

Abstract

The Afar Triangle is located at an active triple junction where the East African Rift System, the Red Sea, and the Gulf of Aden converge. This region presents a unique example of the transition from continental rupture to an oceanic basin. The local continental crust is thinned and faulted, interspersed with intense volcanism. The region features an aulacogen, the Afar Depression, and the Danakil Block, an area that rises above the surrounding regions. Similarly, the basement of the Santos Basin/São Paulo Plateau may be associated with crustal rupture in a region that could have functioned as a triple junction. It consists of stretched continental crust, with a significant occurrence of volcanic rocks that form a prominent region in the distal portions of the basin. The reconstruction of the continental margins of South America and Africa, as well as the African and Arabian margins, in Santos Basin and Afar, suggests an apparent overlap of continental crust in both cases, possibly related to a crustal rupture characteristic of a low-angle crustal-scale shear zone. This process is consistent with asymmetric rifting, in which the footwall edge defines the main rift escarpment. In fact, the horizontal misalignment between the loci of mechanical and thermal subsidence, as evidenced by stratigraphy, points to an asymmetric rifting in the Santos Basin. In both regions, asymmetric crustal rupture created a complex mosaic of faults and transfer zones that compartmentalized rift distribution and generated exceptional fluid permeability conditions, especially for upwelling hydrothermal fluids. In the Santos Basin, the pre-Alagoas unconformity reflects crustal uplift and erosion. The topography was not completely leveled, allowing for the preservation of residual relief, which served as a source area for the deposition of carbonate clastic facies in the interval corresponding to Barra Velha Fm. This sedimentary interval records the establishment of a restricted lacustrine system, a precursor to the deposition of the overlying evaporitic layers. This carbonate and evaporitic sedimentation observed in the pre-salt of the Santos Basin presents remarkable similarities with the depositional processes active in the Afar Depression. The arid environment and intense hydrothermal activity are also convergent characteristics between the Afar Depression and the paleoenvironmental context of the pre-salt. More than any other factor, this similarity seems to originate precisely from their analogous tectonic contexts, which also give rise to similar morphologies between the faults and transfer zones present in the Afar Depression and those occurring in Tupi, Júpiter, and Pau-Brasil highs region (Santos Basin). The hypothetical superposition of the Afar region, preserving its scale and conveniently adjusted over the Santos Basin, suggests the possible existence of an aulacogen in the Alto de Ponta Grossa region. The fact that the projected aulacogen crosses the Mato Rico region, where gas occurs in the Paraná Basin, suggests that this structure may have influenced the petroleum system in that basin, an aspect that warrants further investigation. This study aims to demonstrate that the Afar Triangle is an appropriate analogue for understanding both the crustal rupture process that gave rise to the Santos Basin and its tectono-sedimentary evolution, especially in the pre-salt interval.