Riachão Ring is a

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. It lies within the

Parnaíba Basin The Parnaíba Basin (Portuguese: ''Bacia do Parnaíba'') is a large cratonic sedimentary basin located in the North and Northeast portion of Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the ...

. It is in diameter and the age is estimated to be less than 200 million years (

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

or younger). The crater is exposed at the surface. The structure was first identified from analysis of orbital photographs acquired during the

Apollo–Soyuz Apollo–Soyuz was the first crewed international space mission, carried out jointly by the United States and the Soviet Union in July 1975. Millions of people around the world watched on television as a United States Apollo spacecraft docked ...

Test Project in 1975. A reconnaissance investigation of the structure was reported by J. F. McHone in 1977. The structure of the site (dipping

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

along the rim) supported interpretation of an impact origin, but no

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. They are evidence that the rock has been subjected to a shock with pressures in the rang ...

s or

shocked quartz Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pla ...

were found at the time. The crater is severely eroded and there is apparently no

ejecta Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma ...

remaining. The crater rim rises about 50 m above the surrounding surface, and a central uplift is about 30 m above the annular depression within the rim. Shock deformation has been identified in quartz grains within the central uplift.THE RIACHÃO RING IMPACT STRUCTURE, NORTHEASTERN BRAZIL: RE-EVALUATION OF ITS STRATIGRAPHY AND EVIDENCE FOR IMPACT
M. V. Maziviero, M. A. R. Vasconcelos, A. M. Góes, A. P. Crósta, and W. U. Reimold. 43rd Lunar and Planetary Science Conference (2012). File:Riachão Ring AST-23-1931.jpg, Part of 1975 discovery photo (AST-23-1931) of the Riachão Ring, by astronauts of the

Test Project File:Riachão structure D3C1214-401435A010.jpg, 1978 panoramic camera subframe

References

Impact craters of Brazil Jurassic impact craters Landforms of Maranhão Geology of Brazil {{regional-geology-stub