Impactites from Monturaqui Impact Crater

Impactite is

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

created or modified by one or more impacts of 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 ...

. Impactites are considered

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...

, because their

source material A source text is a text (sometimes oral) from which information or ideas are derived. In translation, a source text is the original text that is to be translated into another language. Description In historiography, distinctions are commonly m ...

s were modified by the heat and pressure of the impact. On Earth, impactites consist primarily of modified terrestrial material, sometimes with pieces of the original meteorite.

Creation

When a large meteorite hits a planet, it can radically deform the rocks and

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

that it hits. The heat, pressure, and shock of the impact changes these materials into impactite. Only very massive impacts generate the heat and pressure needed to transform a rock, so impactites are created rarely.

Characteristics

Impactite includes shock-metamorphosed target rocks, melts (

suevite Suevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event. It forms part of a group of rock types and structures that are known as imp ...

s) and mixtures of the two, as well as sedimentary rocks with significant impact-derived components (shocked mineral grains,

tektites Tektites (from grc, τηκτός , meaning 'molten') are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz ...

, anomalous geochemical signatures, etc.). In June 2015, NASA reported that impact glass has been detected on the planet

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

. Such material may contain preserved signs of ancient life—if life existed. Impactites are generally classified into three groups: shocked rocks, impact melt, and impact breccias.

Shocked rock

Shocked rocks have been transformed by

shock metamorphism Shock metamorphism or impact metamorphism describes the effects of shock-wave related deformation and heating during impact events. The formation of similar features during explosive volcanism is generally discounted due to the lack of metamorp ...

caused by the impact. They include

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 and high-pressure minerals, for example

coesite Coesite is a form ( polymorph) of silicon dioxide Si O2 that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first synthesized by Loring Coes Jr., a chemist at the N ...

and

stishovite Stishovite is an extremely hard, dense tetragonal form (Polymorphism (materials science), polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in ...

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. If the liquid cools and hardens quickly into a solid, impact glass forms before the atoms have time to arrange into a

crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...

. Impact glass can be dark brown, almost black, and partly transparent. 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.

Impact breccias

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 ...

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

Examples of impactite

PIA19673-Mars-AlgaCrater-ImpactGlassDetected-MRO-20150608

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

Alamo bolide impact The Alamo bolide impact occurred 377–378 million years ago, when one or more hypervelocity objects from space slammed into shallow marine waters at a site that is now the Devonian Guilmette Formation of the Worthington Mountains and Schell Creek ...

(Late Devonian), Nevada, United States * Alga crater on the planet

Barringer crater Meteor Crater, or Barringer Crater, is a meteorite impact crater about east of Flagstaff, Arizona, Flagstaff and west of Winslow, Arizona, Winslow in the desert of northern Arizona, United States. The site had several earlier names, and fr ...

, Arizona, United StatesMeteor Crater Bomblets
/ref> *

Charlevoix impact structure The Charlevoix impact structure is a large eroded meteorite impact structure in the Charlevoix region of Quebec, Canada. Only part of the impact structure is exposed at the surface, the rest lying beneath the Saint Lawrence River. Description ...

, Québec, Canada *

Darwin Crater Darwin Crater is a suspected meteorite impact crater in Western Tasmania about south of Queenstown, just within the Franklin-Gordon Wild Rivers National Park. The crater is expressed as a rimless circular flat-floored depression, in diamet ...

, Tasmania (source of

Darwin glass Darwin glass is a natural glass found south of Queenstown in West Coast, Tasmania. It takes its name from Mount Darwin in the West Coast Range, where it was first reported, and later gave its name to Darwin Crater, a probable impact crater, and ...

) *

Lake Lappajärvi Lappajärvi is a lake in Finland, in the municipalities of Lappajärvi, Alajärvi and Vimpeli. It is formed in a wide, partly eroded meteorite impact crater. The lake is part of Ähtävänjoki ( sv, Esse å) basin together with Lake Evijärvi th ...

, Finland (source of Kärnäite) *

Manicouagan impact structure Manicouagan Reservoir (also Lake Manicouagan) is an annular lake in central Quebec, Canada, covering an area of . The lake island in its centre is known as René-Levasseur Island, and its highest point is Mount Babel. The structure was created ...

, Québec, Canada *

Neugrund crater Neugrund is a meteorite crater in Estonia. It is in diameter and was previously estimated to have been formed in the Ordovician around 470 Ma, with later research revealing a possible Cambrian origin (around 535 Ma). The crater is at the bottom ...

, Estonia *

Nördlinger Ries The Nördlinger Ries is an impact crater and large circular depression in western Bavaria and eastern Baden-Württemberg. It is located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located within the depression, a ...

crater, Germany *

Rochechouart impact structure Rochechouart impact structure or Rochechouart astrobleme is an impact structure in France. Erosion has over the millions of years has mostly destroyed its impact crater, the initial surface expression of the asteroid impact leaving highly deform ...

, France *

Stac Fada Member The Stac Fada Member is a distinctive layer towards the top of the Mesoproterozoic Bay of Stoer Formation, part of the Stoer Group (lowermost Torridonian Supergroup) in northwest Scotland. This rock unit is generally thick and is made of sandst ...

, Scotland *

Wabar craters The Wabar craters are impact craters located in Saudi Arabia first brought to the attention of Western scholars by British Arabist, explorer, writer and Colonial Office intelligence officer St John Philby, who discovered them while searching for ...

, Saudi Arabia

References

External links

Meteorite crater glossary
Metamorphic rocks Sedimentary rocks Meteorite mineralogy and petrology Impact event minerals Glass in nature {{Meteorite-stub