Figure 19. Ar-Ne isotope plot (after Marty et al., 1999).
Notice relatively low
40Ar/36Ar ~3,000 ratio measured in a mantle "end-member''
together with the least contaminated Ne. This ratio is somewhat lower than the
model-derived lower mantle values and much lower than values inferred from
observation for the upper mantle,
40,000 (see Tolstikhin and Marty, 1998, and
references therein). Extrapolation could lead to a somewhat higher value for the
mantle source. However the extrapolation trends and even possibility of the
extrapolation are not clear.