Coupled thermo-mechanical 3D subsidence analysis along the SW African passive continental margin

Abstract

Sedimentary basins along the SW African margin deliver information about processes, which occurred in the past and serve as a good starting point for reconstructing the margin's evolution. By integrating detailed information on the present-day configuration of the SW African margin into a 3D thermo-mechanical forward modelling framework, we attempt a margin-wide reconstruction of its subsidence history since its onset during breakup.The 3D forward modelling approach as applied on the SW African margin area makes use of the coupling between thermal relaxation of the lithosphere and flexural isostatic balance in response to sediment deposition and build-up of thermal stresses during lithosphere cooling.On the one hand, our results provide useful information about the behavior of the lithosphere during break-up and the subsequent post-rift phase. On the other hand, restored 2 paleobathymetries for specific time intervals during the post-rift evolution give evidence for possible uplift events superposed on the long-term subsidence history of the margin. Restored paleobathymetries are in agreement with conclusions derived from former studies and provided strong indications for the presence of a rather heterogeneous crustal configuration of the margin marked by a mechanical decoupling of the upper and lower crustal domains during most of the rifting phase.

Evidence for active upper mantle flow in the Atlantic and Indo-Australian realms since the Upper Jurassic from hiatus maps and spreading rate changes

“…Reports on the latter assign Upper Cretaceous ages to peak sediment flux (e.g. [81–83]) around the SAP, increased kimberlite occurrence in southern Africa [84], and basin inversion and margin tilting along the Namibian coast [85,86], consistent with a Late Cretaceous SAP uplift pulse inferred from thermochronological studies [87,88]. No major coeval activity is indicated for the Tristan hotspot.…”

Evolution of the Southwestern Angolan Margin: episodic burial and exhumation is more realistic than long-term denudation

“…These processes already entering the rift stage would also account for tectonic and surface uplift and exhumation of the rift shoulders in the proximal domain, and thus support the pronounced cooling observed in our models. Many other mechanisms such as flexural uplift by isostatic rebound (Weissel and Karner 1989;Van Der Beek et al 1994;Burov and Cloetingh 1997), lower crustal flow (Burov and Cloetingh 1997;Péron-Pinvidic and Manatschal 2008;Aslanian et al 2009;Dressel et al 2016;Brune et al 2017), and mantle convection or plume-related processes (Buck 1986;Ebinger et al 1989;Friedrich et al 2018) may also have played an important role; however, the weight attributed to each of these distinct mechanisms may not be established in this work.…”

Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

“…About 130 Ma the continental lithosphere broke apart and generated the South Atlantic Ocean (Larson and Ladd, 1973;Rabinowitz and LaBrecque, 1979;Unternehr et al, 1988;O'Connor and Duncan, 1990;Nürnberg and Müller, 1991;Brown et al, 1995;Talwani and Abreu, 2000;Blaich et al, 2009). These processes were followed by rifting and post-breakup cooling, resulting in several sedimentary basins formed along the margins of the South Atlantic (Stewart et al, 2000;Macdonald et al, 2003;Séranne and Anka, 2005;Dressel et al, 2016).…”

“…The sedimentary units at both settings are predominantly composed of siliciclastic rocks with varying degrees of compaction (Stewart et al, 2000;Brekke, 2000;Scheck-Wenderoth et al, 2007;Scheck-Wenderoth and Maystrenko, 2008;Maystrenko et al, 2013). The crustal configuration of these sedimentary basins and their evolution during different tectonic phases are partly discussed controversially (Stewart et al, 2000;Macdonald et al, 2003;Fernandez et al, 2005;Lundin and Doré, 2011;Koopmann et al, 2014;Nirrengarten et al, 2014;Gernigon et al, 2015;Dressel et al, 2016;Mjelde et al, 2016;Maystrenko et al, 2017). However, all concepts agree with respect to the presence of seaward-dipping reflections near the continent-ocean transition of a thick sedimentary succession above thin crystalline crust beneath the margins and a high-velocity high-density lower crustal body below the distal margins.…”

“…In this context the nature of the lower crustal highvelocity high-density bodies and the role of mantle dynamics for post-breakup vertical movements are especially debated. For the margins along the South Atlantic the lower crustal bodies are predominantly interpreted as the relicts of breakup-related mafic underplating (gabbros), whereas in the North Atlantic the serpentinized mantle and eclogites as a reminder of earlier orogenies are discussed as alternative explanations (White and McKenzie, 1989;Eldholm et al, 2000;Gernigon et al, 2004;Ebbing et al, 2006). Autin et al (2016) have examined the thermal implications of these different hypotheses for the South Atlantic Argentine margin and concluded that only a serpentinite composition would imply a significantly colder thermal field, whereas eclogite and gabbro have similar thermal effects.…”