Fluid inclusions in diamond

Volatiles and Flnids in Diamonds 2.05.4.4.1 Fluid inclusions in diamonds... 

Based on the work of Philippot et al. (1998), one might expect to observe a certain proportion of chlorine-rich fluid inclusions in mantle-derived xenoliths, but inclusions in these xenoliths are overwhelmingly C02-rich, and chlorine-rich inclusions have not been reported (cf. reviews by Roedder, 1984 Pasteris, 1987 Andersen and Neumann, 2001), with the intriguing exception of the brines reported as inclusions in some diamonds (Johnson et al., 2000 Izraeli et al., 2001). The lack of direct observation of chlorine-rich fluid inclusions in mantle-derived xenoliths may be a result of the lack of examination of appropriate samples that record a previous history as subducted oceanic crust, an absence of these fluids in deeper samples because of participation of these fluids in other petrological processes, such as melt production, or because such fluids do not survive subduction below the slab dehydration limit. Conversely, the presence of chlorine in fluid inclusions in diamonds argues for the existence of chlorine-rich fluids at least in some circumstances in the mantle in the pressure range of diamond stability. 

Raman Microspectroscopy. Raman spectra of small solids or small regions of solids can be obtained at a spatial resolution of about 1 J.m using a Raman microprobe. A widespread application is in the characterization of materials. For example, the Raman microprobe is used to measure lattice strain in semiconductors (30) and polymers (31,32), and to identify graphitic regions in diamond films (33). The microprobe has long been employed to identify fluid inclusions in minerals (34), and is increasingly popular for identification of inclusions in glass (qv) (35). 

Recently, it was demonstrated in a diamond anvil cell that Shewanella oneidensis and Escherichia coli strains remain physiologically and metabol-ically active at pressures of 680 to 16,800 bars for up to 30 h (Sharma et al. 2002). At pressures of 12,000 to 16,000 bars, living bacteria resided in fluid inclusions in Ice VI crystals and continued to be viable when pressure returned to 1 bar. However, only 1% remained alive whether this constitutes viability or survival under pressure is contentious (Couzin 2002). Nevertheless, it demonstrates that pressure may not be much of an impediment for some life forms, and that even the deep ocean of Ganymede might be suitable for life. 

Izraeli E. S., Harris J. W., and Navon O. (2001) Brine inclusions in diamonds a new upper mantle fluid. Earth Planet. Sci. Lett. 187, 323-332. 

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. 

Finally, sulfide is a common inclusion in diamonds (cf. Chapter 2.05), and sulfide-bearing fluids/melts have been suggested to be the medium from which diamond crystallizes (e.g., Bulanova, 1995). 

Turner G., Burgess R., and Bannon M. (1990) Volatile-rich mantle fluids inferred from inclusions in diamond and mantle xenolith. Nature 344, 653-655. 

Navon, O., Hutcheon, D., Rossman, G. R., Wasserburg, G. J. (1988) Mantle-derived fluids in diamond micro-inclusions. Nature, 335, 784-9. 

Figure 13. Microbial activity and viability in ice-VI at 1.4 GPa. (A) Complete view of the sample chamber with ice-VI phase with bacteria. Clearly visible is the vein-like structure surrounding the ice phase. (B) Close-up view showing the ice-VI crystal boundary surrounded by clusters of bacteria (Shewanella MRl) within organic-rich veins. (C) After approx. 1 hour, textural changes in the ice occur, defined by the formation of organic-rich inclusions within ice crystals. (D) Close-up view of the fluid inclusions containing clusters of motile bacteria. (E) Upon decompression (to <100 MPa), the viable bacteria (dyed with methylene blue) are seen clustered at the diamond surface but are still observed to be motile.

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