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The upper mantle beneath the South Atlantic Ocean, South America and Africa from waveform tomography with massive data sets

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This publication discusses a detailed study of the Earth's structure beneath the South Atlantic, South America, and Africa. Researchers used data from over 1.2 million seismic measurements to create a 3D map of the Earth's crust and upper mantle.Their findings reveal complex structures beneath these regions. For example, in South America, they found that the Earth's crust varies in thickness and composition under different areas. The study also shows that some regions have thick, solid blocks called cratons, while others have hot, flowingrock beneath.Under Africa, the Earth's crust is more broken up than previously thought, with different cratons within the continent. In the South Atlantic, the research sheds light on interactions between the underwater Mid-Atlantic Ridge and hotspots, which are areas with volcanic activity.One important discovery is that some regions in the South Atlantic have hotter-than-average rock beneath the Earth's surface, which corresponds to the locations of certain hotspots. Additionally, the study provides insights into the depth of the Argentine Basin.This research is crucial for understanding the Earth's structure, which has implications for geological processes, resource exploration, and the study of plate tectonics. It helps scientists better grasp the complex and dynamic nature of our planet.

# metadata.dc.description[].value
Cette publication présente une étude détaillée de la structure de la Terre sous l'Atlantique Sud, l'Amérique du Sud et l'Afrique. Les chercheurs ont utilisé les données de plus de 1,2 million de mesures sismiques pour créer une carte en 3D de la croûte terrestre et du manteausupérieur.Leurs résultats révèlent des structures complexes sous ces régions. En Amérique du Sud, par exemple, ils ont constaté que l'épaisseur et la composition de la croûte terrestre varient selon les régions. L'étude montre également que certaines régions possèdent des blocs épais et solides appeléscratons, tandis que d'autres sont recouvertes de roches chaudes et fluides.Sous l'Afrique, la croûte terrestre est plus fragmentée qu'on ne le pensait, avec différents cratons à l'intérieur du continent. Dans l'Atlantique Sud, les recherches mettent en lumière les interactions entre la dorsale médio-atlantique sous-marine et les points chauds, qui sont des zones d'activitévolcanique.Une découverte importante est que certaines régions de l'Atlantique Sud ont des roches plus chaudes que la moyenne sous la surface de la Terre, ce qui correspond à l'emplacement de certains points chauds. En outre, l'étude permet de mieux comprendre la profondeur du bassin argentin.Cette recherche est essentielle pour comprendre la structure de la Terre, ce qui a des implications pour les processus géologiques, l'exploration des ressources et l'étude de la tectonique des plaques. Elle aide les scientifiques à mieux saisir la nature complexe et dynamique de notreplanète.

# metadata.dc.description.abstract[].value
We present a tomographic model of the crust, upper mantle and transition zone beneath the South Atlantic, South America and Africa. Taking advantage of the recent growth in broadband data sampling, we compute the model using waveform fits of over 1.2 millionvertical-component seismograms, obtained with the automated multimode inversion of surface, S and multiple S waves. Each waveform provides a set of linear equations constraining perturbations with respect to a 3-D reference model within an approximate sensitivity volume. We then combine allequations into a large linear system and solve it for a 3-D model of Sand P-wave speeds and azimuthal anisotropy within the crust, upper mantle and uppermost lower mantle. In South America and Africa, our new model SA2019 reveals detailed structure of the lithosphere, with structure of the cratonswithin the continents much more complex than seen previously. In South America, lower seismic velocities underneath the transbrasilian lineament (TBL) separate the high-velocity anomalies beneath the Amazon Craton from those beneath the Sao Francisco and Parana Cratons. We image the buried portionsof the Amazon Craton, the thick cratonic lithosphere of the Parana and Parnaiba Basins and an apparently cratonic block wedged between western Guyana and the slab to the west of it, unexposed at the surface. Thick cratonic lithosphere is absent under the Archean crust of the Sao Luis, Luis Alves andRio de La Plata Cratons, next to the continental margin. The Guyana Highlands are underlain by low velocities, indicating hot asthenosphere. In the transition zone, we map the subduction of the Nazca Plate and the Chile Rise under Patagonia. Cratonic lithosphere beneath Africa is more fragmentedthan seen previously, with separate cratonic units observed within the West African and Congo Cratons, and with cratonic lithosphere absent beneath large portions of Archean crust. We image the lateral extent of the Niassa Craton, hypothesized previously and identify a new unit, the Cubango Craton,near the southeast boundary of the grater Congo Craton, with both of these smaller cratons unexposed at the surface. In the South Atlantic, the model reveals the patterns of interaction between the Mid-Atlantic Ridge (MAR) and the nearby hotspots. Low-velocity anomalies beneath major hotspots extendsubstantially deeper than those beneath the MAR. The Vema Hotspot, in particular, displays a pronounced low-velocity anomaly under the thick, high-velocity lithosphere o f the Cape Basin. A strong low velocity anomaly also underlies the Cameroon Volcanic Line and its offshore extension, betweenAfrica and the MAR. Subtracting the global, age-dependent Vs averages from those in the South Atlantic Basins, we observe areas where the cooling lithosphere is locally hotter than average, corresponding to the location of the Tristan da Cunha, Vema and Trindade hotspots. Beneath the anomalouslydeep Argentine Basin, we image unusually thick, high-velocity lithosphere, which suggests that its anomalously great depth can be explained, at least to a large extent, by isostatic, negative lithospheric buoyancy.

# metadata.dc.identifier.citation[].value
Celli, N. L., Lebedev, S., Schaeffer, A. J., Ravenna, M. & Gaina, C. (2020). The upper mantle beneath the South Atlantic Ocean, South America and Africa from waveform tomography with massive data sets. Geophysical Journal International, 221, 1, 178-204. https://doi.org/10.1093/gji/ggz574

# metadata.dc.title[].value
The upper mantle beneath the South Atlantic Ocean, South America and Africa from waveform tomography with massive data sets

# metadata.nrcan.secondaryserial.title[].value
Natural Resources Canada, Contribution Series