3D shear wave velocity and radial anisotropy structure of the African Okavango Rift and adjacent regions
The incipient Okavango Rift is one of the youngest rifts of the East African Rift System.Understanding the structure and deformation beneath the rift can enhance our knowledge of early-stage structural features and rifting mechanisms of the entire rift system.In the study,we collected continuous waveform data from 41 broadband seismic stations and used an ambient seismic noise tomography technique to obtain Rayleigh and Love wave phase velocity dispersion data.By inverting these dispersion data,we developed 3D shear wave velocity and radial anisotropy models from the surface to the depth of 50 km.Results show that the middle crust of the Okavango Rift exhibits low velocity and negative radial anisotropy(VSH＜VSV),suggesting the presence of melts in the crust.However,high velocities observed in the lower crust of the rift indicate that these melts may not be sourced from the underlying mantle.Therefore,our results do not support the theory that the rifting was initiated by the intruded mantle-sourced materials.Our radial anisotropy model shows that the lower crust and uppermost mantle beneath the rift possesses positive radial anisotropy(VSH＜VSV),together with the previous investigations,we infer that the rifting might be initiated by the horizontal tectonic stresses from the relative intra-plate movements within a preexisting weak zone.Additionally,the negative radial anisotropy observed in the middle and lower crust of the southwestern Zimbabwe Craton agrees with the previously proposed model that the crust of this region was thickened by the intrusion of the mafic Okavango Dyke Swarm.
万方数据
维普
