Publication Date:
2023-01-19
Description:
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.
Description:
Plain Language Summary:
Passive margins mark the transition zone from a continent to the ocean without being an active boundary of tectonic plates. They are typical for all continents on the globe. In the South Atlantic, the passive margins are located adjacent to the eastern coastline of South America and the western coastline of Africa. Studying the architecture of passive margins is essential for understanding plate tectonic history of the earth because they define how the continents once fitted together and how they broke apart. Passive margin segments on opposite sides of an ocean form so called conjugate margin pairs. Most geophysical studies of passive margins focus on the first few kilometers under the surface. However, their deeper extension to the base of the rigid shell of the earth, known as lithospheric thickness, is to a large extent unknown. Based on a simple temperature model, we find that the lithospheric thickness is highly variable and shows large variations along the South Atlantic passive margins. These differences are associated with the extension of conjugate margin pairs: where one margin is narrower than the conjugate, its lithospheric thickness is greater. This asymmetry indicates that the geodynamic processes, causing the breakup of the two continents, must have been asymmetric as well. Offshore Angola, the lithosphere is modeled shallow and matches with relatively young rock signatures. This suggests additional tectonic activity on the African side after the breakup between the two continents occurred.
Description:
Key Points:
A simple thermal lithosphere‐asthenosphere boundary (LAB) model for the South Atlantic passive margins has been developed.
The LAB model shows distinct variations along the margins that correlate with margin widths.
Conjugate margin pairs reflect an asymmetry in LAB depth patterns that are locally related to post‐breakup lithospheric thinning.
Description:
Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659
Description:
https://doi.org/10.5880/GFZ.1.3.2020.006
Description:
https://www.earthbyte.org/webdav/ftp/Data_Collections/Muller_etal_2019_Tectonics/
Description:
https://doi.org/10.5281/zenodo.7074000
Description:
https://earthbyte.org/webdav/ftp/Data_Collections/Haas_etal_2022_Tectonics/
Keywords:
ddc:551.13
;
passive margins
;
South Atlantic
;
thermal LAB
;
rift asymmetry
;
Gondwana
Language:
English
Type:
doc-type:article
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