A 3D model of first-order structural elements of the Vredefort Dome, South Africa - Importance for understanding central uplift formation of large impact structures

摘要

Based on detailed structural mapping, geophysical information and structural consideration, we generated a 3D structural model of a segment of the Vredefort Dome. This model provides insight into the mechanism of mass transfer during central uplift formation of large impact structures. The model consists of geometrically and kinematically linked km-scale radial and concentric faults that affected the overturned limb of the rim syncline to the Vredefort Dome. The faults accomplished constrictional (centripetal) rock flow followed by radial spreading of uplifted and gravitationally unstable rocks in the crater centre. More specifically, concentric faults formed likely as normal faults during transient crater rim collapse, steepened and were transformed to reverse faults during central rock uplift and finally, were overturned during gravitational collapse of the central uplift. Radial faults, by contrast, formed at a later stage of convergent rock flow towards the crater centre and retained largely their orientation during central uplift formation. Displacement on individual faults is up to 2 km. Cumulative displacement, notably on concentric faults, can account for the large displacement magnitudes predicted by numerical models.