Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation

Abstract

Abstract-The structural, topographic and other characteristics of the Vredefort, Sudbury, and Chicxulub impact structures are described. Assuming that the structures originally had the same morphology, the observations/interpretations for each structure are compared and extended to the other structures. This does not result in any major inconsistencies but requires that the observations be scaled spatially. In the case of Vredefort and Sudbury, this is accomplished by scaling the outer limit of particular shock metamorphic features. In the case of Chicxulub, scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring. The observations/interpretations are then used to construct an integrated, empirical kinematic model for a terrestrial peak-ring basin. The major attributes of the model include: a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor, some of which are pre-existing structures that have been reactivated during transient cavity formation; inward-directed motions along the same outermost structures and along a set of structures, at intermediate radial distances, during transient cavity collapse; structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift, during uplift collapse. The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.

The formation of peak rings in large impact craters

“…Structural data from a number of exposed terrestrial impact structures supports the idea of dynamic collapse of the central uplift (9,(22)(23)(24) and that, in larger craters, the peak ring is formed from the interaction of two collapse regimes (25). In the simulation, the final crater ( Fig.…”

The formation of peak-ring basins: Working hypotheses and path forward in using observations to constrain models of impact-basin formation

“…In the Vredefort impact basin, the inner structural collar appears to be upturned in a manner similar to the overthrusted, collapsed, portions of the central peak (Lana et al, 2003), as modeled in simulations; however, the current erosional and deformational state of the Vredefort impact basin precludes a full reconstruction of its original structure. A review of the Vredefort structure by Grieve et al (2008) additionally suggests that collapsed wall materials of the transient cavity do not appear to extend beneath outwardly thrusted material in the center of the basin as is observed at Chicxulub.…”

“…Other important crater types in this transition include protobasins, which possess both a central peak and a peak ring (Figure 1b). There has been considerable debate on the processes controlling the formation of peak rings on the Moon and terrestrial planets (Pike, 1988;Melosh, 1989;Spudis, 1993;Grieve et al, 2008;. New image and altimetry data have permitted a reassessment of the origin of lunar peak-ring basins and their relationship to smaller complex craters and larger multi-ring basins (Baker et al 2011a(Baker et al , 2012.…”

Volume 364: Chicxulub: Drilling the K-Pg Impact Crater

“…Peak rings are rings of hills that are emergent above crater floors within large impact basins on terrestrial planets ( Figure F1), and there is no consensual agreement on either their formational mechanism or the nature of the rocks that comprise them (Grieve et al, 2008;Baker et al, 2016). Geophysical data indicate that the peak ring at Chicxulub is formed from rocks that have low velocity and density, and one explanation for this is that they are highly fractured and porous (Morgan et al, 2000(Morgan et al, , 2011Gulick et al, 2013).…”