Peridotites carbonatites

FREE enrichment in clinopyroxene is widely linked to metasomatism by either silicate melts or carbonatitic fluids, usually via cryptic (in the sense of no new phase being introduced) metasomatism, although there is a strong possibility that the diopside itself could have precipitated from the melt. This is strongly favored for much of the ubiquitously FREE-enriched diopside found in cratonic peridotites (Figure 17) which are not in trace-element equilibrium with their coexisting garnets and for which equilibrium melts for the diopside closely resemble kimberlite (Simon et al., 2003). 

Neumann E.-R., Wulfif-Pedersen E., Pearson N. J., and Spencer E. A. (2002) Mantle xenoliths from Tenerife (Canary Islands) evidence for reactions between mantle peridotites and silicic carbonatite melts inducing Ca metasomatism. J. Petrol. 43, 825-857. 

Yaxley G. M., Crawford A. J., and Green D. H. (1991) Evidence for carbonatite metasomatism in spinel peridotite xenoliths from western Victoria, Austraha. Earth Planet Set Lett 107, 305-317. 

Excesses of Re and Al of the magnitude shown by sample 10-12A are expected for bulk addition of a metasomite of broadly basaltic composition to the peridotite (Carlson et al. 1999). In contrast, most Kaapvaal peridotites that show Re addition do not have excess Al, suggesting that the Re addition in this case was caused by an Al-poor melt such as carbonatite, the host kimberlite, or similar composition magmas or fluids (Carlson et al. 1999 Pearson 1999 ). 

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