Ай тас тау жыныстарындағы KREEP құрауышысы: калий, лантидалар және фосфор

Geochemical component of some lunar rocks, potassium, lanthanides, and phosphorus

KREEP, an acronym built from the letters K (the atomic symbol for potassium), REE (rare earth elements) and P (for phosphorus), is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat enhanced concentration of a majority of so called "incompatible" elements (those that are concentrated in the liquid phase during magma crystallization) and the heat producing elements, namely radioactive uranium, thorium, and potassium (due to presence of the radioactive 40K).

The typical composition of KREEP includes about one percent, by mass, of potassium and phosphorus oxides, 20 to 25 parts per million of rubidium, and a concentration of the element lanthanum that is 300 to 350 times the concentrations found in carbonaceous chondrites. Most of potassium, phosphorus and rare earth elements in KREEP basalts are incorporated in the grains of the phosphate minerals apatite and merrillite.

Before the mission of Lunar Prospector lunar satellite, it was commonly thought that these KREEP materials had been formed in a widespread layer beneath the crust. However, the measurements from the gamma ray spectrometer on board this satellite showed that the KREEP containing rocks are primarily concentrated underneath the Oceanus Procellarum and the Mare Imbrium. This is a unique lunar geological province that is now known as the Procellarum KREEP Terrane. Basins far from this province that dug deeply into the crust (and possibly the mantle), such as the Mare Crisium, the Mare Orientale, and the South Pole–Aitken basin, show only little or no enhancements of KREEP within their rims or ejecta. The enhancement of heat producing radioactive elements within the crust (and/or the mantle) of the Procellarum KREEP Terrane is almost certainly responsible for the longevity and intensity of mare volcanism on the nearside of the Moon.