Geologic and geophysical characterization of Vargeão Dome impact structure, SC

Author(s)

César Kazzuo Vieira

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências
• Defense date: 2009-12-02

Examining board members

Alvaro Penteado Crósta; Ticiano José Saraiva dos Santos; Ricardo Ivan Ferreira da Trindade

• Advisor: Alvaro Penteado Crósta; Alfonso Schrank

Abstract

Domo de Vargeão (SC), with a diameter of 12.4km, is a partially eroded complex impact structure formed on the lava flows of the Serra Geral Formation in the Paraná Basin. The anomalous occurrence of sandstones in its interior is related to the presence of the Botucatu and Pirambóia formations, uplifted from their regular stratigraphic level, sitting at approximately 1 km below the present surface. The objective of this study comprises the geologic and geophysical characterization of the Domo de Vargeão using remote sensing, geophysical and geological data integration, on a regional (1:250.000) and local (1:50.000) scale. Magnetic and seismic data analysis allowed: (i) to interpret it as shallow structure, with a strongly deformed zone underneath; (ii) to associate the magnetic high at the center of the structure to the occurrence of melt-fragment breccia; (iii) to associate the annular magnetic low located near the rim of the structure to the occurrence of large blocks of the Ácidas Chapecó unit. The integration of magnetic and remote sensing data (SRTM, Landsat/ETM+, Terra/ASTER, Radarsat-1) with geologic information unveiled a complex system of normal faults associated with the rim of Domo de Vargeão, responsible for the collapse of the blocks of Ácidas Chapecó towards the interior of the structure. The geologic data allowed: (i) to map the area of occurrence breccias and to characterize them as pseudotachylitic breccias; (ii) to identify and characterize impact features such as shatter cones in basalt and sandstone, and planar deformation features (PDFs) in quartz grains; and (iii) to measure the crystallographic direction of the PDFs along planes (0001), {11¯11} and {11¯12}. In conclusion, Domo de Vargeão constitutes a rare example on Earth of a complex impact structure formed in basic and acidic volcanic rocks. Its good exposure and easy access makes this impact structure potentially important for conducting analogous studies of planetary surfaces, thus helping to understand the evolutionary processes of solid bodies such as the Moon, Mars, Venus, among others. (AU)