• New models of sedimentary basins and depth to the Moho of South America were developed to improve lithospheric modeling • Deep depleted roots under the Amazon, Paranapanema and São Francisco cratons are evident from models of lithospheric temperatures, densities and composition • Depletion south of the Paranapanema Craton indicates a previously larger extent of the craton Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Cratons are the ancient continental cores, around which continents accrete and grow. They are stable for billions of years, and due to their geologic evolution often provide an abundancy of resources, for example, rare earth elements and diamonds. Cratons are usually underlain by thick continental lithosphere, their so-called "roots", which can reach up to about 250 km into the Earth (e.g., Steinberger & Becker, 2018). With a few exceptions (Kaban et al., 2015), these roots resist mantle convection, and thus deviate mantle flow. Therefore, a better understanding of cratons, their evolution and dynamics may provide further insight to large-scale dynamic and tectonic processes. Cratons appear to be buoyant with respect to the underlying mantle despite the fact that their long-term cooling causes an increase in density. A commonly cited explanation is the iso-pycnic hypothesis (Jordan, 1978) that is based on the counter-balancing effect of chemical buoyancy. The density increase caused by reduced temperatures is balanced by density decrease from depletion in heavy constituents, mostly iron (Fe;Griffin, O'Reilly, Natapov, & Ryan, 2003). Depletion is commonly measured by means of Mg#, the percentage of Magnesium (Mg) in the total amount of Mg and Fe (100*Mg/(Mg + Fe)) in mantle minerals. Mg#s around 89 are common for fertile mantle rocks, while strongly depleted samples exhibit values around 94 (Griffin, O'Reilly,

Cratons are the ancient continental cores, around which continents accrete and grow. They are stable for billions of years, and due to their geologic evolution often provide an abundancy of resources, for example, rare earth elements and diamonds. Cratons are usually underlain by thick continental lithosphere, their so-called "roots", which can reach up to about 250 km into the Earth (e.g., Steinberger & Becker, 2018). With a few exceptions (Kaban et al., 2015), these roots resist mantle convection, and thus deviate mantle flow. Therefore, a better understanding of cratons, their evolution and dynamics may provide further insight to large-scale dynamic and tectonic processes. Cratons appear to be buoyant with respect to the underlying mantle despite the fact that their long-term cooling causes an increase in density. A commonly cited explanation is the iso-pycnic hypothesis (Jordan, 1978) that is based on the counter-balancing effect of chemical buoyancy. The density increase caused by reduced temperatures is balanced by density decrease from depletion in heavy constituents, mostly iron (Fe;Griffin, O'Reilly, Natapov, & Ryan, 2003). Depletion is commonly measured by means of Mg#, the percentage of Magnesium (Mg) in the total amount of Mg and Fe (100*Mg/(Mg + Fe)) in mantle minerals. Mg#s around 89 are common for fertile mantle rocks, while strongly depleted samples exhibit values around 94 (Griffin, O'Reilly,

<p>The presented model describes the lithospheric state of the cratonic regions of Africa in terms of temperature, density and composition based on joint analysis of gravity and seismic data. In addition, a new model of depth to the Moho was calculated from available seismic data. It was then used in combination with data on topography, sediments, and deep mantle anomalies to obtain residual mantle gravity and residual topography. These residual fields were corrected for thermal effects based on S-wave tomography and mineral physics constraints, assuming a juvenile mantle. Afterwards, the thermally corrected fields are jointly inverted to uncover potential compositional density variations. Following the isopycnic hypothesis, negative variations in cratonic areas are interpreted to be caused by iron depletion. Adapting the initially juvenile mantle composition allows to iteratively improve the thermal and compositional variations, culminating in a self-consistent model of the African lithosphere. Deep depleted lithospheric roots exist under the Westafrican, northern to central Congo, and Zimbabwe Cratons. The temperatures in these areas range from below 800 °C at 100 km depth to 1200 °C at 200 km depth. Higher temperatures and absence of depletion at depths below 100 km in wide areas of the eastern to southern Congo and the Kaapvaal Cratons indicate a thinner and strongly reworked lithosphere.</p>

<p>We present an integrated model of the cratonic lithosphere of South America. Gravity and seismic data were jointly analyzed using mineral physics constraints to assess state and evolution of the cratonic roots in South America in terms of temperature, density and composition. At the cratons, our model enables separation of two counteracting effects: the increased density due to cooling with age and decreased density due to depletion of iron. The depletion of iron can be described by the Mg# which gives the partition of Mg<sup>2+</sup> among the double positive ions. A new crustal model (including depth to the Moho) based on existing seismic data was used to correct the gravity field for crustal effects and to uncover the gravity signal of the mantle. In addition, residual topography was calculated as a measure of the part of topography not balanced by the crustal density variations and depth to the Moho. Temperatures within the lithospheric mantle were estimated based on seismic velocities and mineral physics equations, initially assuming a juvenile mantle composition (Mg# of 89). The residual fields were corrected for the respective effects. In the following inversion of residual gravity and topography, we have determined additional density variations which can be interpreted as compositional ones. Furthermore, these results were employed to recompute the upper mantle temperatures taking into account possible compositional changes in the cratonic roots. In this iterative procedure, a consistent thermo-compositional model of the upper mantle has been obtained. Negative compositional density variations imply depletion of iron, leading to higher Mg#s. The highest depletion occurs in the Amazonas and São Francisco Cratons reaching values in the cratons’ centers of up to 90 (Mg#). At the same time, their centers show very low temperatures, down to 600° C in the depth of 100 km. They stay below 1300° C even at a depth of 200 km, indicating deep lithospheric roots. Higher temperatures are found in the Andean forelands and along the Trans-Brasiliano-Lineament (TBL), dividing the Amazonas and São Francisco Cratons. Compositional density variations yield smaller to no amounts of depletion in the Amazonas Craton below a depth of 100 km. The São Francisco Craton still shows depletion in 200 km depth (Mg# up to 89.5). Slightly negative compositional density variations southwest of the São Francisco Craton also exist at depths up to 200 km, indicating the Paranapanema cratonic fragment.</p>

The architecture and evolution of passive margins have been extensively studied over the last decades (e.g.,

The lithospheric architecture of passive margins is crucial for understanding the tectonic processes that caused the breakup of Gondwana. We highlight the evolution of the South Atlantic passive margins by a simple thermal lithosphere‐asthenosphere boundary (LAB) model based on onset and cessation of rifting, crustal thickness, and stretching factors. We simulate lithospheric thinning and select the LAB as the T = 1,330°C isotherm, which is calculated by 1D advection and diffusion. Stretching factors and margin geometry are adjusted to state‐of‐the‐art data sets, giving a thermal LAB model that is especially designed for the continental margins of the South Atlantic. Our LAB model shows distinct variations along the passive margins that are not imaged by global LAB models, indicating different rifting mechanisms. For example, we model up to 200 km deep lithosphere in the South American Santos Basin and shallow lithosphere less than 60 km in the Namibe Basin offshore Africa. These two conjugate basins reflect a strong asymmetry in LAB depth that resembles variations in margin width. In a Gondwana reconstruction, we discuss these patterns together with seismic velocity perturbations for the Central and Austral Segments of the margins. The shallow lithosphere in the Namibe Basin correlates with signatures of the Angola Dome, attributed to epeirogenic uplift in the Neogene, suggesting an additional component of post‐breakup lithospheric thinning.

<p>In this contribution, we examine the evolution of the South Atlantic passive margins, based on a new thermal lithosphere-asthenosphere-boundary (LAB) model. Our model is calculated by 1D advection and diffusion with rifting time, crustal thickness and stretching factors as input parameters. The initial lithospheric thickness is defined by isostatic equilibrium with laterally variable crustal and mantle density. We simulate the different rifting stages that caused the opening of the South Atlantic Ocean and pick the LAB as the T=1330° C isotherm. The modelled LAB shows a heterogeneous structure with deeper values at equatorial latitudes, as well as a more variable lithosphere along the southern part. This division reflects different stages of the South Atlantic opening: Initial opening of the southern South Atlantic caused substantial lithospheric thinning, followed by the rather oblique-oriented opening of the equatorial South Atlantic accompanied by severe thinning. Compared to global models, our LAB reflects a higher variability associated with tectonic features on a smaller scale. As an example, we identify anomalously high lithospheric thickness in the South American Santos Basin that is only poorly observed in global LAB models. Comparing the LAB of the conjugate South American and African passive margins in a Gondwana framework reveals a variable lithospheric architecture for the southern parts. Strong differences up to 80 km for selected margin segments correlate with strong gradients in margin width for conjugate pairs. This mutual asymmetry suggests highly asymmetric melting and lithospheric thinning prior to rifting.</p>