Late Modification-Stage Tectonic Deformation of the Popigai Impact Structure, Russia

Abstract.

The 35-Ma-old Popigai impact structure (about 100 km in diameter) is characterized by its good preservation state and exposure, and detailed investigations that were made through deep drilling and mapping. The present contribution shows data on the post-impact faulting in the Popigai crater that were obtained from detailed mapping combined with aerial photo interpretation. The fracturing of impact rock bodies is widespread throughout the crater. Two hierarchic groups of fracture deformations are distinguished: (1) Main radial and concentric impact-related faults, which determine a block structure of the crater; (2) Small-size local faults and fissures from 0.5 to 5.5 km in length and from some centimeters to 10–20 m wide within impact rock sequences. There is no preferred orientation of individual local fractures, but fault systems have near-radial or near-concentric directions. As a typical example, an intensely fractured impact melt body was mapped at the 1:16,000 scale. Local fracture deformations originated during the compaction of strongly inhomogeneous sequences of impact rocks, whereas block faulting has been caused by both regional tectonic movements, i.e., the uplifting of the Anabar Shield, and, to a lesser content, by relaxation processes. Thus, the 35 -Ma-long post-impact modification history of the Popigai crater is determined by the superimposition of the regional tectonics on the long-term relaxation movements. As a whole, the late modification stage tectonics is found to have only an insignificant effect to the Popigai crater, so that both the original structure and the crater topography have been retained in a good state.