Modal melting 350 index

The modal abundances of ohvine, orthopyroxene, clinopyroxene and spinel observed for spinel peridotites from six well-characterized olf-craton xenolith suites are plotted against a depletion index in Figures 3(a)-(c). The amount of ohvine correlates negatively with degree of depletion, as expected because olivine is a product of the reaction that produces melt at the solidus (Figure 2) (see Chapter 2.08). The number of samples compiled (n = 143) may not be completely representative, but there is nonetheless a suspicious population gap at 2 wt.% AI2O3. 

Figure 3 Modal abundances in (a-c) off-craton and (d-f) on-craton xenoliths as a function of depletion (indexed by wt.% AI2O3). Shown for illustrative purposes are calculated modal variations in residues as a function of melt fraction for melting at 1.5 GPa (a-c) and 3 GPa and 7 GPa (d-f) using empirical methods in Canil (2002).

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