Riachão Ring

Template:Short description Template:Infobox terrestrial impact site

The Riachão Ring is a meteorite impact crater in Brazil. It lies within the Parnaíba Basin. It is Template:Convert in diameter and the age is estimated to be less than 200 million years (Jurassic or younger). The crater is exposed at the surface.<ref name=EIDBRiachaoRing>Template:Cite Earth Impact DB</ref>

The structure was first identified from analysis of orbital photographs acquired during the Apollo–Soyuz Test Project in 1975.<ref>R. S. Dietz and J. F. McHone, 1977, Volcanic Landforms and Astroblemes. In Apollo–Soyuz Test Project Summary Science Report, Volume II, Earth Observations and Photography Edited by Farouk El-Baz and D. M. Warner. Prepared by NASA Lyndon B. Johnson Space Center. NASA Special Publication 412.</ref> A reconnaissance investigation of the structure was reported by J. F. McHone in 1977.<ref>J. F. McHone, 1977, Riachão Ring, Brazil: A Possible Meteorite Crater Discovered by the Apollo Astronauts. In Apollo–Soyuz Test Project Summary Science Report, Volume II, Earth Observations and Photography Edited by Farouk El-Baz and D. M. Warner. Prepared by NASA Lyndon B. Johnson Space Center. NASA Special Publication 412.</ref> The structure of the site (dipping breccia along the rim) supported the interpretation of an impact origin, but no shatter cones or shocked quartz were found at the time.

The crater is severely eroded and there is apparently no ejecta remaining. The crater rim rises about Template:Convert above the surrounding surface, and a central uplift is about Template:Convert above the annular depression within the rim. Shock deformation has been identified in quartz grains within the central uplift.<ref>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).</ref>