  the araguainha crater or araguainha dome is an impact crater on the border of mato grosso and goiÃ¡s states, brazil, between the villages of araguainha and ponte branca. with a diameter of , it is the second largest known impact crater in south america, and possibly the oldest one. the crater has most recently been dated to 254.7&nbsp;Â±&nbsp;2.5 million years ago, when the region was probably a shallow sea. the margins of error of this date overlap the time of the permianâtriassic extinction event, one of the largest mass extinction events in earth's history. the impact punched through paleozoic sedimentary units belonging to the paranÃ¡ basin formations, and exposed the underlying ordovician granite basement rocks. it is estimated that the crater was initially  wide and  deep, which then widened to  as its walls subsided inwards. ==description== araguainha is a complex crater with annular and radial faults, exposed to the surface and eroded, crossed by the araguaia river. the crater has an uplifted central core, shaped like an elliptical basin, consisting of exposed basement granite. surrounding this core is a ring of shocked granite and overlying breccias; then another ring of ridges and mountains,  in diameter and up to  high, consisting of folded and steeply tilted devonian sandstones. this central region is surrounded by an annular depression floored by rocks from devonian and carboniferous sandstone formations. the outer rim of the crater consists of remnants of semi-circular grabens in highly deformed permo-carboniferous sediments. evidences of impact origin include shatter cones, impact breccias, and shocked quartz. ==dating, interpretation, and effects== the earliest report on the araguainha structure was published in 1969 by northfleet et al., who interpreted it as an uplift of the phanerozoic sediments caused by a cretaceous syenite intrusion. a reconnaissance geological survey by silveira filho and ribeiro (1971) noted the occu
Earth_Impact_Database Impact_craters_of_Brazil Triassic_impact_craters