Hydrogen, oxygen and silicon isotope systematics in lunar material

Abstract

In this review the following conclusions are supported: (1) The bulk of the hydrogen in the lunar soils represents protons implanted from the solar wind and is essentially deuterium free. (2) Rarely samples of relatively detuerium rich hydrogen are found, probably resulting from in situ spallation reactions. (3) The water found in lunar samples is probably entirely terrestrial contamination (which yields a third component of hydrogen in the lunar samples). (4) Extreme l8O and 30Si enrichments are found in the surfaces of grains in the lunar soil. These probably result from the condensation of material which was vaporized from the lunar surface by bombardment from micrometeorites, etc., and fractionated in the lunar atmosphere, leaving a heavy isotope enriched fraction to condense. The complimentary fraction enriched in light isotopes escapes and about 1 % of the mass of the regolith has been lost in this way. (5) Oxygen isotope geothermometry on lunar basalts gives temperatures in the approximate range 1000-1150 °C generally close to experimentally determined liquidus temperatures. (6) Recent oxygen isotope studies by Clayton and co-workers provide exciting new evidence that the Earth-Moon system has a different origin from the higher temperature condensates in the chondritic meteorites.