The Permo-Triassic Araguainha impact structure (central Brazil): impact products and collapse history in the central peak-ring

A meteorite impact hit central Brazil ca. 250 Ma ago, just prior to the Permo-Triassic boundary, leaving a 40 km wide complex impact structure (the largest impact structure identified in South America). It is a well-preserved and shallowly eroded crater, developed on sediments of the intracratonic Parana basin. The impact has excavated more than 2 km of the original sedimentary pile, bringing to the surface granites and host metamorphic rocks of the crystalline basement after collapse. It comprises a central peak ring, annular basin, two main ring features and deformed rims. Field observations and petrographic studies in impact-related materials inside the central peak ring allow recognition of six lithofacies (porphiritic-granite, foliated-granite, partially-molten granite, melt, polymitic breccias and pseudotachylytes) that record different magnetic fabrics. Porphiritic granite preserved the original igneous fabric orientation, whereas the other rocks record crater collapse, comprising foliated granites bellow a lid of strongly deformed partially molten rocks covered by breccias and melts. Comparison of these observations with available models of crater collapse will be discussed.