Impact structure

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Impact crater structure Craterstructure.gif
Impact crater structure

An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface expression of an impact structure. In many cases, on Earth, the impact crater has been destroyed by erosion, leaving only the deformed rock or sediment of the impact structure behind. [1] This is the fate of almost all old impact craters on Earth, unlike the ancient pristine craters preserved on the Moon and other geologically inactive rocky bodies with old surfaces [2] in the Solar System. Impact structure is synonymous with the less commonly used term astrobleme meaning "star wound". [3]

Contents

In an impact structure, the typical visible and topographic expressions of an impact crater are no longer obvious. Any meteorite fragments that may once have been present would be long since eroded away. Possible impact structures may be initially recognized by their anomalous geological character or geophysical expression. These may still be confirmed as impact structures by the presence of shocked minerals (particularly shocked quartz), shatter cones, geochemical evidence of extraterrestrial material or other methods.

See also

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Susan Elizabeth Werner Kieffer is an American physical geologist and planetary scientist. Kieffer is known for her work on the fluid dynamics of volcanoes, geysers, and rivers, and for her model of the thermodynamic properties of complex minerals. She has also contributed to the scientific understanding of meteorite impacts.

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<span class="mw-page-title-main">Multi-ringed basin</span> Crater containing multiple concentric topographic rings

A multi-ringed basin is not a simple bowl-shaped crater, or a peak ring crater, but one containing multiple concentric topographic rings; a multi-ringed basin could be described as a massive impact crater, surrounded by circular chains of mountains resembling rings on a bull's-eye. A multi-ringed basin may have an area of many thousands of square kilometres.

<span class="mw-page-title-main">Crater</span> Depression caused by an impact or geologic activity

A crater is a landform consisting of a hole or depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described as: "a bowl-shaped pit that is formed by a volcano, an explosion, or a meteorite impact". On Earth, craters are "generally the result of volcanic eruptions", while "meteorite impact craters are common on the Moon, but are rare on Earth".

References

  1. Neuendorf, K.K.E., J.P. Mehl Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN   0-922152-76-4
  2. Moore, Jeffrey M.; Black, Greg; Buratti, Bonnie; Phillips, Cynthia B.; Spencer, John; Sullivan, Robert (2009). "Surface Properties, Regolith, and Landscape Degradation". In Pappalardo, Robert T. (ed.). Europa. The University of Arizona space science series. McKinnon, William B.; Khurana, Krishan. Tucson: The University of Arizona Press. p. 341. ISBN   978-0-8165-2844-8. Bodies with current geological activity such as Io and Earth have very few recognizable impact craters—Io, in fact, is so volcanically active that not a single impact crater, of any size, has been found on its surface to date. The Earth has about 150 recognized craters, but many have been geologically modified and would be difficult to recognize from orbit. On the other hand, geologically inactive bodies with old surfaces, such as Earth's Moon or Callisto, are covered with impact craters of all sizes.
  3. French, Bevan M (1998). Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. Houston, Texas: Lunar and Planetary Institute. p. 120. LPI Contribution No. 954.