Geodetic Constraints on Cratonic Microplates and Broad Strain During Rifting of Thick Southern African Lithosphere

Southern Africa is typically considered to belong to a single tectonic plate, Nubia, despite active faulting along the southwestern branch of the East African Rift System. We analyze regional Global Navigation Satellite System (GNSS) measurements, and find that the San microplate, situated south of the southwestern branch of the East African Rift, is statistically distinct from Nubia, with 0.4-0.7 mm/yr of extension across the boundary. Adding nine new campaign GNSS sites, we show that the extension rate across the southern Malawi Rift is 2.2 +/- 0.3 mm/yr, with 75% of the relative velocity occurring over 890 km, despite the surface expression of faulting being <150 km wide. Thus, for the first time, we use geodetic measurements to describe the accommodation of strain in broad zones between Archean cratons in southern Africa's thick continental lithosphere.

Automated summary

The study reveals that the San microplate, located south of the southwestern branch of the East African Rift, is statistically distinct from the Nubia tectonic plate with an extension rate of 0.4-0.7 mm/yr. Additionally, new GNSS measurements show that the extension rate across the southern Malawi Rift is 2.2 +/- 0.3 mm/yr, mostly concentrated over 890 km, despite the narrow surface expression of faulting. These geodetic measurements provide insight into the strain accommodation in broad zones within southern Africa's thick continental lithosphere.