Mantle Xenology

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This research seeks to examine the abundances and isotopic composition of Xe trapped from mantle sources. Previous work has shown that mid-ocean ridge basaltic glasses are the most efficient traps, but two complications to the interpretation of the data arise: the possible presence of an atmospheric-like component, and the possibility of mass fractionation of the xenon isotopes. The most important aspect of terrestrial isotopic xenology has been the measurements of an anomaly i the Xe-129/Xe-130 ratio, interpreted as due to the decay of short-lived I-129. Such an interpretation mandates an early-degassing model; i.e., within roughly the first 25 million years of earth history. But the interpretation is clouded by the fact that several authors have found no anomaly, and by the complications referred to above. It is planned to investigate the existence and extent of the anomaly by measurements made in a variety of MORB, to estimate the magnitude of the atmospheric-like component by crushing and stepwise-heating runs, and with simultaneous measurements of Kr isotopic abundances to gain a handle o the possible role of mass fractionation.