Upper mantle viscosity and dynamic subsidence of curved continental margins

Abstract

Continental rifting does not always follow a straight line. Nevertheless, little attention has been given to the influence of rifting curvature in the evolution of extended margins. Here, using a three-dimensional model to simulate mantle dynamics, we demonstrate that the curvature of rifting along a margin also controls post-rift basin subsidence. Our results indicate that a concave-oceanward margin subsides faster than a convex margin does during the post-rift phase. This dynamic subsidence of curved margins is a result of lateral thermal conduction and mantle convection. Furthermore, the differential subsidence is strongly dependent on the viscosity structure. As a natural example, we analyse the post-rift stratigraphic evolution of the Santos Basin, southeastern Brazil. The differential dynamic subsidence of this margin is only possible if the viscosity of the upper mantle is 42-3

Computational Geodynamics of South American Plate: Contributions and Perspectives

“…Along with the coupled numerical models of surface processes and the flexural-isostatic response of the lithosphere, other geodynamic models were used or developed at USP, considering other rheological behavior besides the elastic component, exploring in detail how the stress field varies in depth. Using the CitcomCU numerical code (Moresi and Gurnis, 1996;Zhong, 2006) to simulate convection in the upper mantle, Sacek and Ussami (2013) showed how the curvature of the continental lithosphere can affect the contribution of edge-driven convection in the asthenosphere and the lateral thermal conduction along divergent continental margins, showing how these two effects probably affected the subsidence pattern along the Santos Basin in southeastern Brazil. The first model developed at USP that explored non-linear rheologies was the finite element visco-elastic model presented by Assumpção and Sacek (2013), showing how variations in the crustal thickness in the interior of Central Brazil can produce flexural stresses in the lithosphere with amplified effects close to the Earth's surface, explaining the observed seismicity in the upper crust.…”

Composition of the Sub‐Cratonic Mantle of the Guiana Shield Inferred From Diamond‐Hosted Inclusions

“…Model viscosity curves were derived using ∼35 ppm H 2 O following Hirth and Kohlstedt (2003) and Li et al (2008) along surface heat flows of 49, 35, and 40 mW m −2 . The viscosity range for the asthenosphere (dark gray zone) is from Peslier et al (2017); the mean viscosity of NE Brazil, off the eastern coastal margin of Amazonian Craton is η ∼ 10 19 Pa•s (Sacek & Ussami, 2013); the mean viscosity of the South American mantle is η ∼ 10 21 Pa•s (Flament et al, 2014); the global upper mantle viscosity values based on glacial isostatic adjustment and other data beneath cratons ranges from η ∼ 10 18 Pa•s (Pollitz, 2003) to 10 22 Pa•s (She & Fu, 2019); The effective viscosity estimated from olivine in mantle xenoliths of the Siberian, Kaapvaal, Tanzanian, and Slave Cratons are included (Baptiste et al, 2012;Doucet et al, 2014;Grant et al, 2007;Hui et al, 2015;Jean et al, 2016;Kilgore et al, 2020;Kurosawa et al, 1997;Kolesnichenko et al, 2016;Peslier et al, 2008Peslier et al, , 2010Peslier et al, , 2017.…”

Dinâmica convectiva na borda de litosfera continental

“…A variação temporal do vigor convectivo depende essencialmente da eficiência relativa do transporte de calor por condução no interior da litosfera e do transporte de calor por convecção na astenosfera, sendo significantemente influenciado pela geometria da borda da placa litosférica (Sacek & Ussami, 2013).…”