Araguainha Impact Crater
Monday, January 25, 2010 2:30:59 PM
Landsat image of the Araguainha crater; screen capture from NASA World Wind
The crater does not show up very well in a satellite image, but with some difficulty it is distinguishable. It is an impact crater on the border of Mato Grosso and Goiás states, Brazil, between the villages of Araguainha and Ponte Branca. With a diameter of 40 km, it is the largest known impact crater in South America, and possibly the oldest one. It is also the best preserved impact crater on the continent. The crater was formed 244.40 ± 3.25 million years ago, when the region was probably a shallow sea. The impact punched through Palaeozoic sedimentary units belonging to the Paraná Basin formations, and exposed the underlying Ordovician granite basement rocks. It is estimated that the crater was initially 24 km wide and 2.4 km deep, which then widened to 40 km as its walls subsided inwards. 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, 6.5 km in diameter and up to 150 m 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.
The impact must have been disastrous for marine organisms living in the Parana basin. During the transition between the permian and Triassic periods the continents were wedged together forming the supercontinent of Pangea. The climate was on average warmer than today. The southern parts of Brazil were covered by a shallow sea that extended over much of Argentina, Uruguay and southern Africa. This sea is known as the Parana Basin in South America and the Karoo Basin in southern Africa.
Lana & Marangoni
The Araguainha impact:a South American Permo-Triassic catastrophic event
Geology Today, January-February 2009, pp. 21-28
Araguainha Dome - The Largest Astrobleme in South America
Impact events and their effect on the origin, evolution, and distribution of life
GSA Today, August 2000, pp. 1–7.
http://www.geosociety.org/pubs/gsatoday/archive/sci0008.htm (free access)
Location: S 16°47', W 52°59'