Rapid South Atlantic spreading changes and coeval vertical motion in surrounding continents: Evidence for temporal changes of pressure-driven upper mantle flow

Abstract

The South Atlantic region displays (1) a topographic gradient across the basin, with Africa elevated relative to South America, (2) a bimodal spreading history with fast spreading rates in Late Cretaceous and Eo‐Oligocene, and (3) episodic regional uplift events in the adjacent continents concentrated in Late Cretaceous and Oligocene. Here we show that these observations can be linked by dynamic processes within Earth's mantle, through temporal changes in asthenosphere flow beneath the region. The topographic gradient implies westward, pressure‐driven mantle flow beneath the basin, while the rapid spreading rate changes, on order 10 million years, require significant decoupling of regional plate motion from the large‐scale mantle buoyancy distribution through a mechanically weak asthenosphere. Andean topographic growth in late Miocene can explain the most recent South Atlantic spreading velocity reduction, arising from increased plate boundary forcing associated with the newly elevated topography. But this mechanism is unlikely to explain the Late Cretaceous/Tertiary spreading variations, as changes in Andean paleoelevation at the time are small. We propose an unsteady pressure‐driven flow component in the asthenosphere beneath the South Atlantic region to explain the Late Cretaceous/Tertiary spreading rate variations. Temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions: we find that this prediction from our models agrees with geologic and geophysical observations of the South Atlantic region, including episodes of passive margin uplift, regional basin reactivation, and magmatic activity.

Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction

“…The plume influence is also suggested by erosion and uplift of the Southern African Plateau in the Late Cretaceous (Fig. 2, label 16; MacGregor 2010; Guillocheau et al 2012;Colli et al 2014). Similar uplift and erosion is also recorded in West Africa (Leprêtre et al 2014).…”

“…Faster African plate motion is associated with a period of increased spreading rate between 120 and 70 Ma in the southern Atlantic (Fig. 2, labels 2, 2b; Cogné and Humler 2006;Conrad and Lithgow-Bertelloni 2007;Colli et al 2014), although the global peak of oceanic crust production is recorded earlier at 120 Ma coeval with the Pacific superplume (Fig. 2, label 3; Larson 1991;Conrad and Lithgow-Bertelloni 2007).…”

The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U‐Th‐Sm)/He thermochronology

“…(top row) Key Late Cretaceous to early Cenozoic magnetic anomalies on WGM2012 global model gravity maps of ocean flow lines for the Mid‐Atlantic Ridge and Southwest Indian Ridge. (bottom left) Spreading rates of South Atlantic opening for different plate reconstruction models from 150 Myr to the present for a point currently located at 57.2°W, 36°S in a reference frame that keeps Africa fixed [after Colli et al, ]. Africa (NGU) and Africa (UTIG) show the absolute velocities of Africa in a mantle reference frame for an approximately conjugate point in the Orange Basin, at 15°E, 27.5°S.…”

“…Recently, new thermomechanical modeling approaches have coupled the vertical forces acting on the base of the lithosphere, in‐plane stresses from plate movements, and the deformational response of a rheologically and structurally heterogeneous lithosphere over different length scales [ Guillou‐Frottier et al, ; Cloetingh et al, ; Buiter and Torsvik , ; Burov and Gerya , ; Colli et al, ; Koptev et al, ]. A fundamental outcome of these modeling approaches is that plate motions, mantle flow, and vertical motions of the surface are all intrinsically linked [ François et al, ; Colli et al, ].…”

PyBacktrack 1.0: A Tool for Reconstructing Paleobathymetry on Oceanic and Continental Crust

“…In order to choose a sensible dynamic topography model for inclusion in backtracking, the pros and cons of the various models need to be taken into account, as well as other regional geological or geophysical observations that may help determine which model may be most reasonable for a give region. One could argue that the anomalous depth of the Argentine Basin is due to some other process, such as shallow asthenospheric flow (Colli et al, 2014), but so far no asthenospheric flow-driven geodynamic model has been developed that successfully predicts the Argentine Basin depth anomaly. There is no single model that best captures dynamic topography in all oceanic regions, and the reader is referred to the two papers that describe the models bundled with pyBacktrack (M€ uller et al, 2018;Rubey et al, 2017).…”