Insights about the formation of a complex impact structure formed in basalt from numerical modeling: The Vista Alegre structure, southern Brazil

1Marcos Alberto Rodrigues Vasconcelos,1Fernanda Farias Rocha,2Alvaro Penteado Crósta,3,4Kai Wünnemann,3Nicole Güldemeister,2Emilson Pereira Leite,3Júlio César Ferreira,3,5Wolf Uwe Reimold
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13298]
1Department of Geophysics, Instituto de Geociências, Universidade Federal da Bahia, Salvador, Brazil
2Instituto de Geociências, Universidade Estadual de Campinas, R. Carlos Gomes 250, 13083‐855 Campinas, Sao Paulo, Brazil
3Museum für Naturkunde—Leibniz‐Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany
4Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany
5Laboratory of Geochronology, Instituto de Geociências, Universidade de Brasília, 10910‐900 Brasília, Federal District, Brazil
Published by arrangement with John Wiley & Sons

We present the outcomes of simulations of the formation of the Vista Alegre impact structure, Paraná Basin, Brazil. The target comprised a thick sequence of volcanic rocks of predominantly basaltic composition of the Serra Geral Formation that had been deposited on top of sedimentary rocks (sandstones) of the Pirambóia/Botucatu formations. The cratering process was modeled using the iSALE shock physics code. Our best‐fit model suggests that (1) the crater was originally ~10 km in size; (2) it was formed in ~115 s by a stony projectile of 1000 m in diameter, for an assumed impact velocity of 12 km s−1; (3) target rocks underwent a peak pressure of ~20 GPa, in agreement with previous petrographic investigations of shock deformation. Furthermore, the model points out that the sedimentary strata below the layer of volcanic rocks were raised by ~650 meters at the central part of the crater, which resulted in the current partial exposure of the sandstones at the surface. The outcomes of our modeling suggest that parameters like cohesion and strength of the target rocks, after shock compression, determined the final morphology of the crater, especially the absence of a topographically prominent central peak. Finally, the results of the numerical modeling are roughly in agreement with gravity data over the structure, in particular with respect to the presence of the uplifted sedimentary strata, which are responsible for a low gravity signature at the center of the structure.

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