Diamonds mantle-derived xenoliths

Kramers J. D. (1979) Lead, uranium, strontium, potassium and rubidium in inclusion-bearing diamonds and mantle-derived xenoliths from southern Africa. Earth Planet. Sci. Lett. 42(1), 58-70. 

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. 

To obtain information on the noble gas state in the mantle, it is necessary to analyze mantle-derived materials that have trapped mantle noble gases. Accessible samples include volcanic rocks, volcanic gases, mantle xenoliths, and diamonds. Among various mantle-derived materials, submarine volcanic rocks are particularly useful because of their wide occurrence and their relatively large (for mantle samples) amounts of trapped noble gases. So far, information has been obtained mainly from... 

The presence of diamond and graphite in mantle-derived samples such as kimberlites and the xenoliths they host is prima facie evidence that neutral carbon is stable in the Earth s mantle. Outstanding questions remain, however, concerning the stability of neutral carbon in areas other than those beneath continental cratons, and concerning the mechanism by which diamond forms. To a large extent, the latter question revolves around the unresolved problem of the oxidation state of the mantle, and how—and if— the oxidation state is controlled. 

Sulfur is almost always present in mantle-derived magmas and mantle samples as sulfide, which has been documented from mantle xenolith suites, abyssal peridotites, peridotite massifs, and diamonds (Meyer and Brookins, 1971 Desborough and Czamanske, 1973 Frick, 1973 Vakhrushev and Sobolev, 1973 Bishop et al., 1975 De Waal and Calk, 1975 Meyer and... 

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