Late Modification Stage Tectonic Deformation of the Popigai Impact Structure Russia

Mikhail S. Mashchak and Mikhail V. Naumov

Karpinsky All-Russia Geological Research Institute (VSEGEI), Sredny prospect 74, 199106 St. Petersburg, Russia ([email protected])

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.

111W liilPO

111W liilPO

Target rocks

Post-impact rocks ~~I Quaternary

Target rocks

Upper Palegzpic and Mesozoic sedimentary and igneous racks

HQtC

Jlmentary Archean basement rocks

Upper Proterozoic and Cambrian sedl rücks

L-1 lithic breccia

Sjuvilu

Massive Impact melt rock (tagarnitej p. '■} Rolymict allogenic I—13—I mega breccia Areas described in detail (1, Balagan-Yuregue Basin II, Mafachika Upland area, III, Chordu-Daldyn area, IV, Tongulakh area, V, Profilny area)

Post-impact rocks ~~I Quaternary

□Neoggne-QuaTemary r^—j Central line I *"i of peak ring

Fig. 1. Schematic geologic map of the Popigai impact structure. Modified after Masaitis et al. (1998). Areas described in detail are shown by shaded quadrangles. The locations of areas that are shown in aerial photographs (Fig. 5-7) are shown by white quadrangles.

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