CRUSTAL STRUCTURE BENEATH THE INCIPIENT OKAVANGO RIFT, BOTSWANA

Rifting describes a process of continental break-up and plays a significant role in the formation and evolution of sedimentary basins. Our current understanding on rifting mechanisms is largely limited to mature rift segments. In order to decipher the processes of rifting at its early stage, we conducted the first teleseismic crustal studies of the world’s youngest continental rifts---the Okavango rift zone (ORZ) where the magma has not yet breached the surface. Here we show using receiver functions and gravity modeling that the crust/mantle boundary beneath the ORZ is uplifted by 4-5 km and the initiation of the ORZ is closely related to lithospheric stretching. Possible decompression melting of the sub-crustal lithosphere occurs beneath the ORZ, which is highlighted with the relatively low upper mantle density based on the gravity modelling and shallow Curie isothermal depths based on magnetic modeling. Our observations helps us better model the rifting mechanisms during its early stage and improve the understanding on the formation of sedimentary basins developing within the rift zones.