Stable and noble gas isotopes

Abstract

There are four main reasons why stable isotopes provide important information about the petrogenesis and source regions of oceanic basalts. Hydrogen, carbon, nitrogen, oxygen and sulphur are essential components of the volatiles which drive all magmatism. Direct mantle nodule samples provide sparse evidence on the host phases of these elements. The study of stable isotopes in oceanic basalts provides a window on these elements in the mantle. Large fractionations of stable isotope ratios exist between the crust, mantle, hydrosphere, atmosphere and the biosphere. Stable isotopes thus provide a tool for studying the dynamics of exchange between these reservoirs. By linking stable isotopes with, in particular, noble gases and radiogenic isotopes, the earth’s degassing history may be studied. Very large stable isotopic effects are observed in meteorites. These provide models of unprocessed planetary material which indicate the possible isotopic heterogeneities in the deep earth. Again, the study of mantle stable isotopes via the vehicle of oceanic basalts may provide a window into deep earth history.