Crustal Structure Across the Okavango Rift, Botswana: The SEISORZ Wide‐Angle Seismic Experiment

Abstract The Okavango Rift Zone (ORZ) is an incipient continental rift in Botswana at the terminus of the Southwestern Branch of the East African Rift System. The lack of syn‐rift magmatism and tectonic processes overprinting pre‐rift structures provide an opportunity to investigate incipient‐stage rift processes and the role of pre‐existing structures in rift initiation and strain localization. We present SEISORZ, a ∼450‐km‐long wide‐angle seismic transect across the ORZ and neighboring tectonic terranes. A 2.5‐D V P tomographic inversion reveals crustal thinning within a ∼130‐km‐wide section of the Damara Belt hosting the ORZ where Moho depth is 38.7 ± 3.4 km, shallower than in other Damara Belt terranes (46.3 ± 1.4 km) and the Kalahari Craton (45.6 ± 2.0 km). Mantle V P is consistent with ultramafic lithologies without evidence for metasomatism, partial melt, or elevated temperatures. Crustal V P is variable but consistent with geological information and with lower‐crustal mafic lithologies. However, beneath the rifting region, the model shows low crustal velocities (Δ V P = −0.26 ± 0.05 km/s) that we interpret as damage from rift‐related faulting and deformation, and to a lesser extent elevated temperatures possibly from excess radiogenic heat production. Upper crustal heterogeneity correlates with known and newly detected intra‐rift faults, suggesting that pre‐existing structures promoted strain localization and establishment of the rift border fault system. Collectively, all these factors point to a rheologically weak section in the Ghanzi‐Chobe zone which is more susceptible to deformation in response to far‐field stresses than neighboring terranes, explaining why incipient rifting is localizing there and not across any other of the terranes that compose the Damara Belt.