Titanium peridotite xenoliths

In a given facies, the sodium and titanium content of clinopyroxene shows a negative correlation with depletion (or chromium content) and can increase substantially in metasomatized xenoliths. The substimtion of sodium, chromium, and aluminum has a complex relationship with T, P and degree of depletion but in general, clinopyroxene from higher P samples contains more sodium. Representative analyses for different peridotite facies are shown in Table 4. 

In natural samples, clinohumite is invariably titanium-rich and often fluorine-bearing (in those cases where fluorine analyzed). There is no apparent systematic composition difference (e.g., Mg/Fe, Ti content) between clinohumites found in massifs and those found in kimberlites and xenoliths. Ulmer and Trommsdorff (1999) argue that titanium-saturated clinohumite has the maximum thermal stability, with titanium-undersatu-rated clinohumite breaking down at lower temperatures in a divariant reaction to form a titanium-saturated clinohumite + olivine + ilmenite + H2O, based on experiments by Weiss (1997) (Figure 9). Because of the dependence of the stability of clinohumite on Ti02, Ulmer and Trommsdorff (1999) argue that the amount of titanoclinohumite in the peridotitic mantle would be controlled by the low Ti02 content... 

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