KREEP is an igneous rock, which is found on the Earth's moon. In particular, it was found in the form of craters or Impaktbrekzien in addition to basalts ( see also Lunabas and lunarite ). These is the chemical composition of the so-called incompatible elements, ie those which do not crystallize from magma with olivine, pyroxene or feldspar. These include the lanthanides and the radioactive elements potassium, uranium and thorium.
Etymology and history
KREEP is an acronym for potassium Rare Earth Elements ( rare earth metals) and phosphorus. Larger pieces of KREEP were collected by the crew of the Apollo missions and brought back to Earth. A similar underground rock is non-existent, according to current knowledge.
As indicated by the name, KREEP consists of about 1% by weight. Potassium oxide and phosphorus oxide, 20-25 ppm rubidium and lanthanum and other lanthanides. The concentration of lanthanum is about 300 to 350 times higher than in stony meteorites. KREEP still contains significant traces of uranium, thorium, zirconium, and fluorine and chlorine. It is important to note that, as usual, in petrology relate the concentration data of the elements, based on the corresponding oxides; actually are and the elements before and silicates.
It is assumed now that KREEP was in the formation of the moon. According to today's popular theories of the moon ( see also origin of the moon ) was created by the impact of a Mars-sized object about in the early Earth about 4.5 billion years.
This impact a large amount terrestrial material was thrown into an orbit around the earth, which then eventually formed the moon.
Because of the impact this large amount of energy released, one can assume that a large part of the young moon was liquid (see lunar magma ocean, engl. ). By slow cooling first crystallized minerals such as olivine and pyroxene from ( Fractional crystallization, or Magmatic differentiation). This fell to the bottom of the lunar mantle. In the next step, anorthite, which due to its lower density rose up and formed the so-called Anorthitkruste on the surface was formed. In this process, the magma is enriched with elements, which were not soluble in the olivine or anorthitreichen phase. KREEP thus formed as an intermediate layer between the Anorthitoberfläche and the olivine, lunar mantle.
Until the Lunar Prospector mission was thought that KREEP can only occur as a homogeneous layer under the lunar crust. The gammaspektroskopischen studies of this mission, however, showed that KREEP is very unevenly distributed on the moon. In Oceanus Procellarum and Mare Imbrium in (see Lunar terrane, engl. ) Can already be found on the surface. Further away from these regions, for example in the Mare Crisium, in Mare Orientale and South Pole - Aitken basin in it is also in ejecta of impact craters, ranging up to the lunar mantle, only moderately represented by little. The enrichment in Oceanus Procellarum and Mare Imbrium in can therefore presumably be due to one, compared to the other areas, long-lasting lunar volcanism.
KREEP, which was found on the moon's surface is a result of meteorite impacts on the lunar surface, which penetrated to the KREEP layer and casting a it to the surface. This KREEP - ejecta are less than 1 cm in the rule. Samples of these were brought by the Apollo 15 mission to Earth. It is believed that these samples were formed in the genesis of Mare Imbrium.
Owing to the presence of radioactive elements, KREEP suitable for dating of lunar rocks. In particular it was thus the age of the lunar volcanoes and age be determined by some craters.
KREEP as ore
Although KREEP is repeatedly mentioned as a possible source of raw materials for rare-earth metals, it should be noted that back are the contents of rare earth metals far behind those underground ores. Since significant geological activities are still recorded on the moon neither an atmosphere exists, a differentiated training of ores or minerals is not possible.