Influence of Peruvian flat-subduction dynamics on the evolution of western Amazonia

Abstract

Convection in the Earth's mantle is mainly driven by cold, dense subducting slabs, but 15 relatively little is known about how 3D variations in slab morphology and buoyancy 16 affect mantle flow or how the surface above deforms in response (i.e. dynamic 17 topography). We investigate this problem by studying the dynamics of an active region of 18 flat-slab subduction located in Peru in South America. Here the slab geometry is well 19 known, based on the regional seismicity, and we have observations from the local 20 geological record to validate our models. Of particular interest is the widespread 21 subsidence and deposition of the Solimões Formation across western Amazonia that This formation covers an extensive area from the foredeep to the Purus Arch located 24 ~2 000 km away from the trench. Close to the Andes the preservation of several 25 kilometers of sedimentary thicknesses can be easily accounted for by flexure. Based on 26 an estimate of the Andean loading we predict 2.8 to 3.6 km of accommodation space that 27 spans 100 km. The spatial and temporal history of the Solimões Formation however, 28 particularly the thick distal foreland accumulations up to 1.2 km deep, can only be 29 matched with the addition of a longer-wavelength dynamic source of topography. 30 Following the transition from normal to flat subduction, we predict over 1 km of dynamic 31 subsidence (~1500 km wide) that propagates over 1000 km away from the trench, 32 tracking the subduction leading edge. This is followed by a pulse of dynamic uplift over 33 the flat segment behind it. We therefore propose that a combination of uplift, flexure and 34 dynamic topography during slab flattening in Peru is responsible for the sedimentation 35 history and landscape evolution of western Amazonia that eventually led to the 36 configuration of the Amazon Drainage Basin we know today.

Dynamic uplift during slab flattening

“…2 and in agreement with our previous results (Dávila et al, 2010;Dávila and Lithgow-Bertelloni, 2013;Eakin et al, 2014). The present-day model shows not only a migration of the topographic wave to the east with respect to the Paleogene model, especially along flat segments, but also a strong reduction in amplitude (Dávila and Lithgow-Bertelloni, 2013, Fig.…”

“…5b would improve the match by a few 100 m. In Peru, unfortunately, the wet climate and dense vegetation have not preserved similar stratigraphic markers to reconstruct the distal foreland paleoelevations. But the arrival of the flat slab coincides with the formation of the Sub-Acre/Solimões basin nearly 1000 km from the trench and changes in the drainage pattern of the Amazon (Eakin et al, 2014).…”

Influence of subduction history on South American topography

“…The amplitude of dynamic topography predicted by different flow models also vary widely depending on model set up and boundary conditions (Thoraval and Richards, 1997;Flament et al, 2013). These challenges in constraining the amplitude of residual and dynamic topography make it important to compare time-dependent model predictions to time-dependent geological constraints.…”

“…There has been significant recent progress in measuring the amplitude of residual topography in the oceanic domain (Winterbourne et al, 2014), but constraining the amplitude of residual topography in the continental domain remains a challenge (Flament et al, 2013). The amplitude of dynamic topography predicted by different flow models also vary widely depending on model set up and boundary conditions (Thoraval and Richards, 1997;Flament et al, 2013).…”

“…South America is an ideal continent to investigate the evolution of subduction-driven long-wavelength dynamic topography (e.g. Lithgow-Bertelloni and Gurnis, 1997;Flament et al, 2013) because subduction has been continuous along its western margin at least since the Jurassic and the last plumerelated large igneous province to be emplaced regionally was the Parana-Etendeka at ∼132 Ma (Bryan and Ferrari, 2013). Several studies have investigated the influence of changes in subduction characteristic on the evolution of the topography of South America since the Miocene (Guillaume et al, 2009;Dávila et al, 2010;Shephard et al, 2010;Lithgow-Bertelloni, 2013, 2015;Eakin et al, 2014).…”