Collapse of large complex impact craters: Implications from the Araguainha impact structure, central Brazil.

The 40-km-wide Araguainha impact structure in central Brazil provides extensive out- crops to study the structural evolution of all parts of a complex crater, including the central uplift, annular trough, and crater rim. While most craters of comparable size are buried by impact-related or postimpact sedimentary deposits, Araguainha is deeply eroded and it exposes in detail outcrop-scale structural features that can be used to understand the structural evolution of large impact craters. This study explores evidence from structural features across the entire impact structure in order to provide constraints on the target rock movement during the crater collapse. Most of the structural features described here are consistent with folding and bedding-parallel shearing during several kilometers of lateral inward movement of the target rocks. Vertical movement was, in contrast, restricted to distances of less than a few hundred meters along radial and concentric fault zones around the crater rim. [ABSTRACT FROM AUTHOR]