CARBON AND PRIMARY HELIUM AND ARGON ISOTO PES IN THE MANTLE ROCKS - GEOCHEMICAL AND COSMOCHEMICAL CONSEQUENCES

The relations between isotopes He-3, Ar-36 and carbon were studied in the mantle rocks from islands and continental rifts, which deliver a m aterial from undegassed PLUM-type reservoir. It was found that the rat ios C/He-3 and C/Ar-36 /He-3 are correlated and under variations of th ese ratios on four orders of magnitude. The C/Ar-36 ratio is constant in the range from 10(9) to 10(10). In this range also fall MORBs, carb onatites and some natural mantle gases. The cosmochemical estimation o f the C/Ar-36 ratio was carried out by studying the collection of mete orites. It was found that only achondrites (including SNS) and metamor phized H- and L-chondrites of high petrological classes have the value s of C/Ar-36 ratio close to the Earth's ones. The study has shown that degassed mantle reservoir is enriched in He-3 relative to both Ar-36 and carbon as compared to undegassed mantle. The model of admixing of the cosmic dust with solar volatiles to the degassed mantle reservoir after the exosphere formation was analyzed. It was found that needed m ass of cosmic dust is less than 10(-6) of the mantle mass. The problem of the deficit relative to He-3 and Ar-36 in the Earth's atmosphere w as also solved in terms of the mixing model which requires an admixing of the cosmic dust with solar gases with low values of C/Ar-36 ratio. The estimation of needed mass of cosmic dust is less than 0.004% of t he Earth's mass. Ne with isotopic ratio Ne-20/Ne-22 is-approximately-e qual-to 9.4 (i.e. lower than atmospheric one) is expected in the undeg assed mantle reservoir.