Kinematics of large terrestrial impact crater formation inferred from structural analysis and three-dimensional block modeling of the Vredefort Dome, South Africa

Field-based structural analyses addressing the formation of large terrestrial impact structures are rare. We present a field-based kinematic analysis and a threedimensional (3-D) block model of prominent structures from supracrustal strata of the Vredefort Dome, the central uplift of the Vredefort impact structure. This study aims to better understand the kinematics of complex crater formation. Specifically, the configuration of prominent concentric and radial faults supports the hypothesis that the Vredefort Dome formed by centripetal rock movement followed by radial spreading of uplifted rocks. Centripetal rock movement led to the formation of radially disposed transpression zones, whereby distorted supracrustal strata are characterized by a remarkable structural continuity during central uplift formation. This continuity points to a rather strong mechanical coherence of strata throughout the process. Distortion of layers at the exposed crustal level was accomplished mostly by folding on the hundred-meter scale and is at variance with the concept of concentric normal faults accomplishing kilometer-scale slip within and toward the center of complex impact structures. Displacement magnitudes calculated for strata exposed in the Vredefort Dome indicate that the diameter of the transient cavity of the Vredefort impact structure was ~70 km at surface. All prominent structural elements of the Vredefort Dome can be explained by central uplift formation.