Abstract
This equation shows that on a plot of ( )
λ θ e , the volcanics erupted from this reservoir should define a straight line whose y intercept (at 2 λ θ e = 0, i.e., in the future at θ = -∞) is 1 (radioactive equilibrium, cf. Fig. 3). A linear relationship is also obtained if isotope ratios, like ( 230 Th/ 232 Th) θ , are reported versus 2 λ θ e (see Fig. 11 in Condomines et al. 1988). This latter diagram is similar to the well known isotope evolution diagrams used in Sr or Nd isotope geochemistry, where 87 Sr/ 86 Sr or 143 Nd/ 144 Nd ratios are reported versus time.