Redefinition of Somalian Plate motion, East African Rift System kinematics, and the tectonic significance of Madagascar

Abstract:

The East African Rift System (EARS) comprises the entire divergent plate boundary separating the Nubian and Somalian plates, which extends from the Red Sea - Gulf of Aden intersection in the north to the Southwest Indian Spreading Ridge to the south. Numerous studies have suggested that most of the extensional strain along the EARS is accommodated in narrow deforming zones that bound the Victoria, Rovuma, and Lwandle microplates. Here, we present results from a new kinematic modeling study that uses data from 25 Global Positioning System (GPS) sites and geologic data along the Southwest Indian Spreading Ridge to constrain the Somalian Plate rotation and to suggest a new tectonic plate geometry for the region. This new model includes a broad zone of diffuse deformation spanning the eastern border of the Rovuma microplate, across the Comoros, and into parts of Madagascar also redefining the kinematics of the Lwandle microplate. The northern Lwandle microplate resides in southern Madagascar, and a small portion of south-central Madagascar moves rigidly with the Somalian plate, thus, Madagascar is breaking up. Extensional deformation across the EARS is accommodated by both diffuse deformation and strain accommodation in narrow zones.