Vargeão Dome
Key facts
- Country
- Brazil
- Diameter
- 12 km
- Age
- about 123 million years
- Location
- 26.83° S, 52.12° W
A round depression about 12 km across in the hills of western Santa Catarina, southern Brazil, with the town of Vargeão on its edge. It stands out clearly from the air.
Vargeão Dome is an impact structure about 12 km across in the state of Santa Catarina, southern Brazil. It is one of very few impact craters on Earth formed in basalt, the dark volcanic rock that makes up most of the surfaces of the Moon's maria and of Mars.
What it hit. The impactor struck the thick lava flows of the Serra Geral basalts, part of one of the largest outpourings of lava in Earth's history, which covered much of southern Brazil about 134 million years ago. Beneath the lavas lay the Botucatu sandstone, formed from ancient desert dunes. The impact uplifted these sandstones in the centre, so they now appear at the surface surrounded by basalt.
Proof of impact. The round structure was noticed on aerial photographs and satellite images. Geologists found shatter cones in both basalt and sandstone, and quartz grains in the sandstone with planar deformation features, produced only by shock. Shocked basalt has also been studied here.
Age. The impact must be younger than the basalts, about 134 million years old. Dating of the impact rocks suggests an age of about 123 million years, though the uncertainty is not small.
Why it matters. Because craters on the Moon and Mars are often formed in basalt, Vargeão and its neighbour Vista Alegre are valuable for understanding how impacts affect such rocks. The impactor is unknown.
Visiting. Much of the structure is farmland. Ask permission before entering private land.
Did you know?
Vargeão is one of very few impact craters on Earth formed in basalt lava.
Sandstone from beneath the lavas was lifted to the surface in its centre.
Basalt like that at Vargeão covers much of the Moon's dark maria.