Vargeao Dome
Encyclopedia
Vargeão Dome is a meteorite
crater
in Santa Catarina State, Brazil, straddling the municipalities of Vargeão
, Faxinal dos Guedes
, and Passos Maia
.
The crater is an almost perfectly circular depression with steep walls, 12 km in diameter and up to 225 m deep relative to its rim. Its age is estimated to be less than 70 million years (Cretaceous
or younger)
The meteorite impacted on the basalt
ic rocks of the Serra Geral Formation (Jurassic
/Cretaceous). The crater displays several concentric rings and radial faults, and an eroded central bulge. The latter consists of impact breccias and sandstones from the Botucatu/Pirambóia Formation (Cretaceous/Triassic
), which have been displaced about 700 m above their mean depth in the surrounding area. At least four post-impact lava flows have been identified between the rim and core. The impact origin of the structure is attested by the presence of shatter cone
s and shocked quartz
grains.
identified an anomalous circular structure in radar images produced by the RADAMBRASIL survey, and called it the Vargeão Dome. In the early 1980s E. Barbour Jr. and W.A.G. Correa
studied the structure in detail, in the context of oil/gas surveys of the area, and proposed a volcanic/tectonic origin for the structure. In 1982, Á. P. Crósta
and A. Paiva Filho identified it as an impact crater. Shocked quartz was identified by M. V. Coutinho in 1987, and the occurrence of maskelynite
glass was reported by J. Hachiro and others in 1993
is locate inside the crater, near the southern rim. Nevertheless, the crater is still well-preserved. The local population is well aware of the impact origin of the structure, to the point that the town's official nickname is Meteor City.
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
in Santa Catarina State, Brazil, straddling the municipalities of Vargeão
Vargeão
Vargeão is a town and municipality in the state of Santa Catarina in the South region of Brazil.-References:...
, Faxinal dos Guedes
Faxinal dos Guedes
Faxinal dos Guedes is a town and municipality in the state of Santa Catarina in the South region of Brazil.-References:...
, and Passos Maia
Passos Maia
Passos Maia is a town and municipality in the state of Santa Catarina in the South region of Brazil.-References:...
.
The crater is an almost perfectly circular depression with steep walls, 12 km in diameter and up to 225 m deep relative to its rim. Its age is estimated to be less than 70 million years (Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
or younger)
The meteorite impacted on the basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic rocks of the Serra Geral Formation (Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
/Cretaceous). The crater displays several concentric rings and radial faults, and an eroded central bulge. The latter consists of impact breccias and sandstones from the Botucatu/Pirambóia Formation (Cretaceous/Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
), which have been displaced about 700 m above their mean depth in the surrounding area. At least four post-impact lava flows have been identified between the rim and core. The impact origin of the structure is attested by the presence of shatter cone
Shatter cone
Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions...
s and shocked quartz
Shocked quartz
Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure , the crystalline structure of quartz will be deformed along planes inside the crystal...
grains.
Discovery and studies
In 1978, Brazilian geologists A. Paiva Filho, C.A.V. Andrade and L.F. Scheibeidentified an anomalous circular structure in radar images produced by the RADAMBRASIL survey, and called it the Vargeão Dome. In the early 1980s E. Barbour Jr. and W.A.G. Correa
studied the structure in detail, in the context of oil/gas surveys of the area, and proposed a volcanic/tectonic origin for the structure. In 1982, Á. P. Crósta
Álvaro Penteado Crósta
Álvaro Penteado Crósta is a Brazilian geologist, specialized in remote sensing and mineral exploration. He is an authority on the meteor craters of Brazil and known for the Crosta method/technique.-Biography:A. P...
and A. Paiva Filho identified it as an impact crater. Shocked quartz was identified by M. V. Coutinho in 1987, and the occurrence of maskelynite
Maskelynite
Maskelynite is a glassy phase found in some meteorites and meteorite impact craters. Typical samples are similar in composition to plagioclase feldspar, and revert to that mineral when melted and recrystallized. It was named after British geologist M.H.N...
glass was reported by J. Hachiro and others in 1993
Conservation status
The area around and inside the crater has been heavely farmed since the end of the 19th century; Vargeão's city hallCity hall
In local government, a city hall, town hall or a municipal building or civic centre, is the chief administrative building of a city...
is locate inside the crater, near the southern rim. Nevertheless, the crater is still well-preserved. The local population is well aware of the impact origin of the structure, to the point that the town's official nickname is Meteor City.