astro.wikisort.org - Meteorite

Impactite is rock created or modified by one or more impacts of a meteorite.[1][2] Impactites are considered metamorphic rock, because their source materials were modified by the heat and pressure of the impact.[3] On Earth, impactites consist primarily of modified terrestrial material, sometimes with pieces of the original meteorite.[3]

Creation

When a large meteorite hits a planet, it can radically deform the rocks and regolith that it hits. The heat, pressure, and shock of the impact changes these materials into impactite.[3] Only very massive impacts generate the heat and pressure needed to transform a rock, so impactites are created rarely.[3]

Characteristics

Impactite includes shock-metamorphosed target rocks, melts (suevites) and mixtures of the two, as well as sedimentary rocks with significant impact-derived components (shocked mineral grains, tektites, anomalous geochemical signatures, etc.). In June 2015, NASA reported that impact glass has been detected on the planet Mars. Such material may contain preserved signs of ancient life—if life existed.[4] Impactites are generally classified into three groups: shocked rocks, impact melt, and impact breccias.[2]

Shocked rock

Shocked rocks have been transformed by shock metamorphism caused by the impact. They include shatter cones and high-pressure minerals, for example coesite and stishovite.

Impact melts

When a meteor strikes a planet's surface, the energy released from the impact can melt rock and soil into a liquid. The liquid then cools and becomes an impact melt.[2] If the liquid cools and hardens quickly into a solid, impact glass forms before the atoms have time to arrange into a crystal lattice. Impact glass can be dark brown, almost black, and partly transparent.[5] Sometimes, the cooled liquid does form a crystal structure. In that case, it would still be considered an impact melt, but not an impact glass.[2]

Impact breccias

Breccia is "a rock consisting of angular fragments cemented together".[6] An impact breccia is formed when a meteor shatters a rock and then cements it back together. Some breccias contain impact melts.[3]

Examples of impactite

Impactite has been found, for example, at the following impact craters and structures:

• Alamo bolide impact (Late Devonian), Nevada, United States
• Alga crater on the planet Mars[4]
• Barringer crater, Arizona, United States[7]
• Charlevoix impact structure, Québec, Canada
• Darwin Crater, Tasmania (source of Darwin glass)
• Lake Lappajärvi, Finland (source of Kärnäite)
• Manicouagan crater, Québec, Canada
• Neugrund crater, Estonia
• Nördlinger Ries crater, Germany
• Rochechouart impact structure, France
• Stac Fada Member, Scotland
• Wabar craters, Saudi Arabia

See also

• Glossary of meteoritics
• Meteorite shock stage
• Vitrified sand

References

External links

• Meteorite crater glossary

На других языках

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- [en] Impactite

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[ru] Импактиты

Импактиты (от англ. impact — «столкновение», «удар») — космогенные горные породы, образовавшиеся в результате ударно-взрывного (импактного) породообразования и ударного метаморфизма при столкновении крупных метеоритов с поверхностью Земли. Локализованы в астроблемах. При образовании импактитов показатели давления и температуры достигают десятков гигапаскалей и 2000—3000°С соответственно, а скорости изменения этих параметров превышают скорости их эволюции в других типах породообразующих процессов на несколько порядков.

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