Diamonds garnet compositions

Because of the buffering effect of mantle olivine on the oxygen isotope composition of metasomatic fluids, oxygen isotopes are not, in most cases, effective tracers of mantle-fluid interaction (Mattey et al, 1994 Menzies and Chazot, 1995). One exception to this is the fluid-process that creates diamond. Comparison of the oxygen isotope compositions of garnets in typical... 

FIGURE 3.12 The composition of the subcontinental lithosphere, (a) Differences in composition between Archaean, Proterozoic, and Phanerozoic subcontinental lithosphere (after Griffin et al., 2003), compared to estimates of the BSE (from Table 3.1). The diamonds represent the average compositions given in Table 3.4. (b) Differences in composition between oceanic and continental lithosphere, as expressed in % modal olivine and olivine mg oceanic peridotites define the trend shown as the dashed line whereas garnet peri-dotites from the Kaapvaal Craton, South Africa - illustrative of Archaean subcontinental lithosphere - plot in the shaded field. The diamonds are the averages of the two fields (after Boyd, 1989). Also shown is the field for Proterozoic subcontinental lithosphere (ellipse) after Griffin et al. (2003). 

Figure 22. Composition plots of coexisting monazite and xenotime. (a) LREE-HREE-Y ternary showing tie lines between coexisting monazite and xenotime. (b) LREE-HREE+Y-(Th+U+Pb) ternary, x = biotite + chlorite zone, = garnet zone, A = staurolite zone, O = sillimanite zone, diamonds = migmatite zone. From Pyle et al. (2001).

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