A Thermo‐Compositional Model of the Cratonic Lithosphere of South America. (22nd April 2021)

• Record Type: Journal Article
• Authors: Finger, N.‐P.; Kaban, M. K.; Tesauro, M.; Haeger, C.; Mooney, W. D.; Thomas, M.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-22
• Subjects: composition -- crustal modeling -- density heterogeneity -- lithosphere -- South America -- thermal modeling; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009307
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: New seismic data on the crust and upper mantle of South America have recently become available and describe its deep structure with unprecedented resolution. Here, seismic data are combined with gravity data and mineral physics constraints to develop self‐consistent models of the temperature, composition, and density of the South American lithospheric and sub‐lithospheric upper mantle. A new model of the crustal structure was developed, including sediment and average crustal density and depth to the Moho. This crustal model was used to correct the gravity field and obtain the residual topography. Then, an initial temperature model, derived from seismic tomography and mineral physics, was improved through an iterative process based on the joint inversion of gravity and residual topography. The results reveal deep cratonic roots present under wide parts of the Amazon, São Francisco, and Paranapanema Cratons, but not under the Rio de la Plata and Parnaíba Cratons. These cratons probably never developed lithospheric roots or were rejuvenated during subsequent tectonic events. We hypothesize that the root of the northwestern Amazon craton was removed by upwelling of hot mantle material under the Guyana highlands. Temperature and density anomalies evident beneath the São Francisco Craton appear to be connected with those of the Paranapanema Craton, which could indicate a westward shift of its root. Depletion south of the Paranapanema Craton probably denotes remnants of a previously larger craton that was rejuvenated by the upwelling of hot mantle material leading to emplacement of the Paraná Flood Basalts. Plain Language Summary: The lithosphere and upper mantle of South America is investigated using multiple data sets, including the topography, crustal structure, regional seismic tomography, gravity, and mineral physics. These data are jointly inverted to estimate variations in temperature, density and composition in the lithospheric and sub‐lithospheric upper mantle to a depth of 325 km. Our results show significant variations in lithospheric properties, including thick, depleted roots beneath large parts of the Amazon, São Francisco, and Paranapanema Cratons. However, portions of some cratons, such as the western Guyana Shield, lack a depleted root. We hypothesize that these regions either never developed a depleted root, or that the root was rejuvenated by lithospheric processes. Key Points: 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