Structural evolution of the 40 km wide Araguainha impact structure, central Brazil

• Grant number: 08/06546-7
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: August 01, 2008
• End date: January 31, 2009
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Carlos Roberto de Souza Filho
• Grantee: Carlos Roberto de Souza Filho
• Host Institution: Instituto de Geociências (IG). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

The 40 km wide Araguainha structure in central Brazil is a shallowly eroded impact craterthat presents unique insights into the final stages of complex crater formation. The dominantstructural features preserved at Araguainha relate directly to the centripetal movement of the targetrocks during the collapse of its transient cavity. Slumping of the transient cavity walls resulted ininward-verging inclined folds and a km-scale anticline in the outer ring of the structure. The foldingstage was followed by radial and concentric faulting, with downward displacement of kilometer-scaleblocks around the crater rim. The central uplift records evidence for km-scale upward movement ofcrystalline basement rocks from the transient cavity floor, and lateral moment of sedimentary targetrocks detached from the cavity walls. Much of the structural grain in the central uplift relates tostructural stacking of km-scale thrust sheets of sedimentary strata onto the core of crystallinebasement rocks. Outward-plunging radial folds indicate tangential oblate shortening of the strataduring the imbrication of the thrust sheets. Each individual sheet records an early stage of folding andthickening due to non-coaxial strains, shortly before sheet imbrication. We attribute this foldingand thickening phase to the kilometer-scale inward movement of the target strata from the transientcavity walls to the central uplift. The outer parts of the central uplift record additional outwardmoment of the target rocks, possibly related to the collapse of the central uplift. An inner ringstructure at 10-12 km from the crater center marks the extent of the deformation related to the outward movement of the target rocks. (AU)