Causes and consequences of asymmetric lateral plume flow during South Atlantic rifting

Abstract

Volcanic rifted margins are typically associated with a thick magmatic layer of seaward dipping reflectors and anomalous regional uplift. This is conventionally interpreted as due to melting of an arriving mantle plume head at the onset of rifting. However, seaward dipping reflectors and uplift are sometimes asymmetrically distributed with respect to the subsequent plume track. Here we investigate if these asymmetries are induced by preexisting lateral variations in the thickness of continental lithosphere and/or lithospheric stretching rates, variations that promote lateral sublithospheric flow of plume material below only one arm of the extending rift. Using three-dimensional numerical experiments, we find that South Atlantic rifting is predicted to develop a strong southward asymmetry in its distribution of seaward dipping reflectors and associated anomalous relief with respect to the Tristan Plume that “drove” this volcanic rifted margin, and that the region where plume material drains into the rift should experience long-lived uplift during rifting—both as observed. We conclude that a mantle plume is still needed to source the anomalously hot sublithospheric material that generates a volcanic rifted margin, but lateral along-rift flow from this plume, not a broad starting plume head, is what controls when and where a volcanic rifted margin will form.

Chemical Geodynamics Insights From a Machine Learning Approach

“…Arguably, the geodynamic setting in the South Atlantic is more complex than in the North and Central Atlantic, with a much larger aerial extent reaching into the Indian Ocean and a large bathymetric swell over several “hot‐spots” (Discovery, Shona, and Bouvet). Nevertheless, recent geodynamic models provide a self‐consistent framework for the distribution of volcanism by the interplay between deep‐sourced mantle upwellings and the motion and lithospheric structure of the African Plate (e.g., Celli et al., 2020; Colli et al., 2018; Gassmöller et al., 2016; Morgan et al., 2020; O’Connor et al., 2018; Sleep, 2002). Capturing of a single mantle upwelling (the Tristan “plume”) into the South Atlantic Ridge leads to a broad region of volcanic activity, and the development of the Walvis Ridge (Gassmöller et al., 2016; O’Connor et al., 2018).…”

Continental tapering of South America caused asymmetric non-uniform opening of the South Atlantic Ocean

“…[8][9][10]. In association with flood basalt eruption at pre-drift hotspots in the Early Cretaceous (137-120 Ma) 1,3,26,32,[40][41][42] , South Atlantic opening initiated with a large-scale asymmetric graben along with gravitational slides and transfer faults in West Gondwana. The splitting of the supercontinent to the tapering continent of South America set the initial boundary condition for South Atlantic opening.…”

Tectono‐stratigraphic evolution of the rift and post‐rift systems in the Northern Campos Basin, offshore Brazil

“…Matos et al (2021) show that such uplift correlates with a thicker pre‐salt package, referred by Figure 4b. The location of Moho uplifts in the SE Brazilian margin is considered to be related to lateral changes in the lithospheric thickness inherited from Brasiliano orogenic assembly that allowed later along rift‐axis flow of plume material (Morgan et al, 2020). The presence of an important basement tectonic limit near the study area (i.e., tectonic limit between the Oriental Terrane of Ribeira belt and the Cabo Frio Tectonic Domain—Figure 1) (Stanton et al, 2019; Strugale et al, 2021) could have worked as such a lithospheric limit.…”