Garnets diamond inclusions

Sobolev, N.V. Shatsky, V.S. 1990. Diamond inclusions in garnets from metamorphic rocks. Nature, 343, 742-746. 

The main silicate inclusions in natural diamond are pyroxenes and garnet [12178-41 -5/, and the understanding of the conditions of their formation from laboratory studies is the basis for the determination of the P—T conditions when diamond was formed (2—6). CO, C02, H2, H O are also found in diamond (20), and it is possible that diamond nucleated and grew in a liquid in a C—H—O system, perhaps immiscible, but in equilibrium with the silicate matrix (4). Graphite [7440-44-0] is also a common inclusion in natural diamond. 

Iherzolite xenoliths with peridotitic garnet inclusions in diamonds and garnets from dia-mondiferous peridotite xenoliths shows that garnets associated with diamonds have significantly lower than garnets in nondiamondi-ferous peridotites (Figure 46 Lowry et al., 1999). 

Figure 60 Cr203 versus CaO (wt.%) content of garnet inclusions in diamond. Original plot and Iherzolite field (dashed) from Soholev et al. (1973). This figure redrafted from plots and database of Stachel et al.

Pearson D. G. and Milledge H. J. (1998) Diamond growth conditions and preservation inferences from trace elements in a large garnet inclusion in a Siberian diamond. Extended Abstracts of 7th Int. Kimb. Conf., Cape Town, pp. 667-669. 

Shimizu N. and Richardson S. H. (1987) Trace element abudance patterns of garnet inclusions in peridotite suite diamonds. Geochim. Cosmochim. Acta 51, 755-758. 

Shimizu N., Sobolev N. V., and Yefimova E. S. (1997) Chemical heterogeneities of inclusion garnets and juvenile character of peridotitic diamonds from Siberia. Russian J. Geol. Geophys. 38(2), 356-372. 

In deeper samples, the trace-element geochemistry observed in garnet inclusions in diamonds has been attributed to carbon-bearing fluids (e.g., Stachel and Harris, 1997 Wang et al., 2000 Dobosi and Kurat, 2002), although the oxidation state of the fluid (CO2- versus CH4-rich) remains open to debate. 

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