Assume that depleted upper mantle and un-depleted lower mantle have the following Nd and He concentrations and isotopic compositions.

Upper Mantle (MORB Source) Lower Mantle 3 He 7.5X108 atoms/g 7.5X1010 atoms/g Nd 0.8 ppm 1.26 ppm 4 He/3 He 80000 20000 eNd 10 0

Using the binary mixing relationships for two isotope ratios, plot the mixing curve between upper mantle and lower mantle in a 4 He/3 He vs. eNd space (For a proper

spread of your calculated data points, use 10% increments between 1-90% of upper mantle, 1% increments between 91 to 99%, and 0.1% between 99.1% to 100%).

A Hawaiian basalt sample has 4 He/3 He = 29600 and eNd = +9.2. Based on your mixing calculation and your mixing curve in 4 He/3 He vs. eNd space, how much lower mantle

component (percentage) is in this sample? Which isotope ratio (Nd or He) gives the clearest signature of the possible presence of a lower mantle component in Hawaii?

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