Redefining East African Rift System kinematics

Abstract

East African Rift System plate geometries and surface motions are some of the least constrained in the context of global plate motion models. In this study, we used GPS data to constrain Somalian plate rotation and to suggest a new tectonic plate geometry for the region. In addition, we tested geologic data from the Southwest Indian Ridge and new GPS data on Madagascar to determine refined kinematics of the Lwandle microplate. A zone of broad deformation was discovered, extending from the eastern boundary of the Rovuma microplate, across the Comoros Islands, and including parts of central and northern Madagascar. Madagascar is fragmenting, with southern Madagascar rotating with the Lwandle microplate and a piece of eastern and south-central Madagascar moving with the Somalian plate. Divergence of the Nubian-Somalian plate system across the East African Rift System involves both diffuse deformation and strain accommodation along narrow rift segments that bound rigid blocks.

Caldera collapse and tectonics along the Main Ethiopian Rift: reviewing possible relationships

“…The direction of extension along the MER was reconstructed by several authors based on structural data and GPS vectors, suggesting a direction of horizontal stretching ranging between N135°E and N105°E [e.g., Chorowicz et al, 1994, Bilham et al, 1999, Chu and Gordon, 1999, Acocella et al, 2002. Nonetheless, other studies suggested a partly different extension direction trending around N90°-100°[e.g., Bonini et al, 1997, Boccaletti et al, 1998, Fernandes et al, 2004, Pizzi et al, 2006, Agostini et al, 2011b, Saria et al, 2014, Stamps et al, 2021. It is well known that elongated calderas may reflect the regional stress field [e.g., Bosworth et al, 2000Bosworth et al, , 2003 and thus extension along the MER may have controlled caldera elongation [Casey et al, 2006].…”

Formation of Continental Microplates Through Rift Linkage: Numerical Modeling and Its Application to the Flemish Cap and Sao Paulo Plateau

“…Eventually, these variabilities may lead to offset rift propagation from opposite directions. Examples of offset rift systems exist along rifted margins, such as in the South Atlantic (Heine et al., 2013), the Jan Mayen microcontinent in the Norwegian‐Greenland Sea (Gernigon et al., 2012), and in the present‐day East African and Red Sea Rift System (Calais et al., 2006; Eagles et al., 2002; Stamps et al., 2008; Stamps et al., 2021). The strike‐perpendicular offset is likely an important factor in how rift segments eventually link, and the structural features that form in response (Allken et al., 2012; Gerya, 2013a).…”

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

“…(b) Our plate angular velocity solution showing the movement of sites used to define the San (yellow shading) and Rovuma (blue shading) relative to stable Nubia (red shading), and the Euler poles from our velocity solution. Orange lines are plate boundaries (adapted fromDaly et al, 2020;Saria et al, 2013;Stamps et al, 2020).…”

“…(b) Our plate angular velocity solution showing the movement of sites used to define the San (yellow shading) and Rovuma (blue shading) relative to stable Nubia (red shading), and the Euler poles from our velocity solution. Orange lines are plate boundaries (adapted from Daly et al, 2020;Saria et al, 2013;Stamps et al, 2020). East residual (mm yr −1 ) ITRF14 Nubia residuals −5000 0 5 000 Elevation (m) proposed additional microplates in southern and eastern Africa (Victoria, Rovuma, and Lwandle) based on bands of earthquakes and active faults along edges of the cratons (Calais et al, 2006;Hartnady, 2002;Horner-Johnson et al, 2007;Stamps et al, 2008), as well as zones of diffuse deformation inconsistent with rigid plates (Stamps et al, 2020).…”

“…Orange lines are plate boundaries (adapted from Daly et al, 2020;Saria et al, 2013;Stamps et al, 2020). East residual (mm yr −1 ) ITRF14 Nubia residuals −5000 0 5 000 Elevation (m) proposed additional microplates in southern and eastern Africa (Victoria, Rovuma, and Lwandle) based on bands of earthquakes and active faults along edges of the cratons (Calais et al, 2006;Hartnady, 2002;Horner-Johnson et al, 2007;Stamps et al, 2008), as well as zones of diffuse deformation inconsistent with rigid plates (Stamps et al, 2020). However, the line of active rifts from southern Tanzania, through the Luangwa and Luano Rifts in Zambia and into the Okavango Rift in Botswana, known as the southwestern branch of the EARS (Figure 1a; Fairhead & Girdler, 1969;Scholz et al, 1976), is not accounted for in current kinematic models.…”