KREEP
200719
225326457
2008-07-13T02:54:29Z
69.138.227.202
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'''KREEP''', an [[acronym]] built from the letters '''K''' (the [[Chemical symbol|atomic symbol]] for the [[Chemical element|element]] [[potassium]]), '''REE''' ([[Rare earth element|'''R'''are '''E'''arth '''E'''lements]]) and '''P''' (for [[phosphorus]]), is a [[Geochemistry|geochemical]] component of some [[lunar impact]] [[Melting|melt]] [[breccia]] and [[basalt]] rocks. Its most significant feature is its inclusion of a majority of so-called "incompatible" elements{{Fact|date=March 2008}} (those that prefer a liquid state during [[Igneous differentiation|magma crystallization]]) and the [[heat-producing element]]s potassium, [[uranium]] and [[thorium]].
Indirectly, the origin of KREEP is a result of the Moon's origin, which is now commonly believed to be a result of a Mars-sized object that impacted the Earth 4.5 billion years ago (see [[Giant impact hypothesis]]). This impact put a large amount of material into circumterrestrial orbit that ultimately reaccreted to form the Moon. Given the large amount of energy that was liberated in this event, it is predicted that a large portion of the Moon would have initially been molten, forming a near-global [[Lunar magma ocean|magma ocean]]. As crystallization of this magma ocean proceeded, minerals such as [[olivine]] and [[pyroxene]] would have precipitated and sunk to form the lunar mantle. After crystallization was about three-quarters complete, anorthositic [[plagioclase]] would have begun to crystallize, and because of its low density, float, forming an anorthositic crust. Importantly, elements that are incompatible (i.e., those that partion preferentially into the liquid phase) would have been progressively concentrated into the magma as crystallization progressed, forming a "KREEP"-rich magma that initially should have been sandwiched between the crust and mantle. Evidence for this scenario comes from the highly anorthositic composition of the lunar highland crust, as well as the existence of KREEP-rich materials.
Before the [[Lunar Prospector]] mission, it was commonly thought that KREEP-rich materials would have formed a near global layer beneath the crust. However, results from the [[gamma ray]] [[spectrometer]] on this mission show that KREEP-containing rocks are primarily concentrated within the region of [[Oceanus Procellarum]] and [[Mare Imbrium]], a unique geological province that is now known as the [[Lunar terranes|Procellarum KREEP Terrane]]. Basins far from this province that excavated deep into the crust (and possibly mantle) such as the [[Mare Crisium|Crisium]], [[Mare Orientale|Orientale]], and [[South Pole-Aitken basin|South Pole-Aitken]] show only modest, or no, enhancements of KREEP within their rims or ejecta. The enhancement of heat producing elements within the crust (and/or mantle) of the Procellarum KREEP Terrane is almost certainly responsible for the longevity and intensity of [[Lunar mare|mare volcanism]] on the nearside of the Moon.
==See also==
* [[Lunar mare]]
* [[Moon]]
* [[Lunar Prospector]]
==References==
<div class="references-small">
* {{cite journal |last=Charles Shearer and 15 coauthors |title=Thermal and magmatic evolution of the Moon |journal=Reviews in Mineralogy and Geochemistry |volume=60 |pages=365–518 |date=2006 |doi=10.2138/rmg.2006.60.4}}
* {{cite journal |last=Mark Wieczorek and 15 coauthors |title=The constitution and structure of the lunar interior |journal=Reviews in Mineralogy and Geochemistry |volume=60 |pages=221–364 |date=2006 |doi=10.2138/rmg.2006.60.3}}
* {{cite journal |title=Major lunar crustal terranes |last=Bradley Jolliff, Jeffrey Gillis, Larry Haskin, Randy Korotev, Mark Wieczorek |journal=[[Journal of Geophysical Research|J. Geophys. Res.]] |date=2000 |pages=4197–4216}}
* {{cite web |url=http://www.psrd.hawaii.edu/Nov05/MoonComposition.html |title=Gamma Rays, Meteorites, Lunar Samples, and the Composition of the Moon | publisher = Planetary Science Research Discoveries | last=G. Jeffrey Taylor |date=November 22, 2005}}
* {{cite web |url=http://www.psrd.hawaii.edu/Aug00/newMoon.html |title=A New Moon for the Twenty-First Century |publisher = Planetary Science Research Discoveries | last=G. Jeffrey Taylor |date=August 31, 2000}}
</div>
==External links==
* [http://www.psrd.hawaii.edu/Archive/Archive-Moon.html Moon articles in Planetary Science Research Discoveries], including articles about KREEP
{{The Moon}}
[[Category:Lunar science]]
[[Category:Mineralogy]]
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