To the Problem About the Origin of Lunar Maria and Continents (Mössbauer Investigations)

A comparative study of Mossbauer spectra of regolith returned by the Luna 16 and Luna 20 spacecraft has shown that the distribution of iron among the mineral phases is quite characteristic of the landing sites. The overall fractions of regolith measured had the following grain sizes: 0.200 to 0.450 mm, 0.127 to 0.200 mm, 0.083 to 0.127 mm, and < 0.083 mm. The Mossbauer spectra of the mare regolith of Luna 16 differ significantly for all fractions from the spectra for the same fractions of continental regolith (Luna 20). The total quantity of iron is 1.85 times greater in the mare regolith. There is 2.4 times less olivine in the mare region than in the continental region and it is higher in iron content (by 1.85 times). The pyroxene component of the mare regolith is less homogeneous in composition (contains more augite and glass) and is present in larger quantities, llmenite was found only in the mare regolith. In the continental region, the predominant titanium-containing phase is ulvospinel. The mare regolith contains more metallic iron, which is more finely dispersed and contains less nickel. Troilite is found in the maria region. Based on these differences, it is concluded that the formation of continental rocks occurred at an earlier stage of crystallization from the melt and at higher temperatures and higher partial pressures of oxygen. The mare basalts crystallized from a more reduced magma, apparently in a later process.