Araguainha
Key facts
- Country
- Brazil
- Diameter
- 40 km
- Age
- 254.7 ± 2.5 million years
- Location
- 16.78° S, 52.98° W
A great ring of hills about 40 km across on the border of Mato Grosso and Goiás, with a central core of granite hills around the small town of Araguainha.
Araguainha is the largest impact structure in South America, about 40 km across, in central Brazil on the border between the states of Mato Grosso and Goiás.
What it hit. The impactor struck the Paraná Basin, a thick sequence of Palaeozoic sandstones, shales and siltstones lying on ancient granite basement. The rebound of the crater floor lifted the granite by about 2 km into a central uplift, now a group of hills about 7 km across. Around it, rings of tilted and faulted sedimentary rock form a series of ridges and valleys.
Proof of impact. At first geologists thought the structure was made by molten rock pushing up from below. In 1973 it was identified as an impact structure, and that origin is confirmed by shatter cones, cone-shaped fractures produced by shock, quartz grains with planar deformation features, and impact melt rock in the central uplift.
Age and extinction. Dating of the melt rock gives an age of about 255 million years, close to the end of the Permian period, when the greatest mass extinction in Earth's history wiped out most species in the sea. Some scientists suggested that Araguainha played a part, perhaps by shattering oil-bearing shales and releasing oil and gas that warmed the climate. Most think the crater was far too small to cause a global catastrophe; the extinction is generally blamed on enormous volcanic eruptions in Siberia.
Why it matters. Araguainha's central uplift is unusually well exposed, making it a key site for studying how large complex craters form. The impactor is unknown.
Visiting. The structure is mostly farmland and grassland. Ask landowners' permission before exploring outcrops.
Did you know?
Araguainha is the largest known impact structure in South America.
Its granite core was lifted about 2 km by the rebound of the crater floor.
It formed close to the time of the end-Permian mass extinction, though it was probably not the cause.