Diamonds isotopic ratios

Fig. 18-24 Observed correlation (the Meteoric Water Line) of the two most important isotopic ratios in precipitation (gray diamonds Jouzel et al., 1987 and Dahe et al., 1994), and predictions of simple isotopic models. A, prediction with constant a B, prediction with temperature-dependent a.

Figure 6.11 38At/36 At isotopic ratios in MORB, OIB, mantle xenolith, and diamonds.

Figure 6.13 Kr isotopic ratios in MORB, OIB, diamond, and mantle xenolith are plotted as percentage deviation from the air Kr isotopic composition. MORB Hiyagon et al. (1992). OIB Hiyagon et al. (1992). Diamond Ozima and Zashu, 1991. Xenolith Poreda and Farley (1992). N number of data analyzed.

Diamonds In bulk collections of large numbers of diamonds, 14N/15N near 400 is typical, confirming their presolar nature by the difference from the terrestrial ratio 272 (but see comments re. Jovian value, above and below). This isotopic ratio (as well as that of C) changes during stepwise combustion of the diamond collection, being much nearer to terrestrial 14N/15N = 272 in the earliest N released. The explanation is not known. 

Some of the chondritic meteorites contain grains (including crystalline and amorphous silicates, diamonds, silicon carbide, graphite, metal oxides, and metal nitrides) that have been identified as presolar based on non-solar isotopic ratios (Zinner 1988 Anders Zinner 1993 Bematowicz et al. 2006), particularly for... 

Busemann H., Baur H., and Wieler R. (2001) Helium isotopic ratios in carbonaceous chondrites significant for the early solar nebula and circumstellar diamonds Lunar Planet. Sci. XXXII, 1598. Lunar and Planetary Institute, Houston (CD-ROM). 

Deines P., Harris J. W., and Gurney J. J. (1997) Carbon isotope ratios, nitrogen content and aggregation state, and inclusion chemistry of diamonds from Jwaneng, Botswana. Geochim. Cosmochim. Acta 61(18), 3993-4005. 

Harte B., Fitzsimons I. C. W., Harris J. W., and Otter M. L. (1999a) Carbon isotope ratios and nitrogen abundances in relation to cathodoluminescence characteristics for some diamonds from the Kaapvaal Province S. Africa. Mineral. Mag. 63(6), 829-856. 

Figure 10 Events during the termination of the most recent glacial period, as recorded in the Dome C ice core. The top curve (5D) is a proxy for local temperatures, showing the Antarctic Cold Reversal (ACR). The solid circles represent CO2 (means and error bars of six samples each). The diamonds represent CH4 (uncertainty is 10 ppb). The depth scale at the top refers only to the CO2 and CH4 records. Bars indicate the Younger Dryas (YD) and Bolling/Allerod (B/A) events, which are recorded in the isotope ratios of Greenland ice cores (Monnin et al. (2001) reproduced hy permissionofthe American Association for the Advancement of Science from Science, 2001,29i, 112-114 (figure 1)).

Meteorites contain a variety of trapped noble gas components other than the solar wind. In many cases their compositions have not been measured in pure form, but have been determined from measured (i.e., not pure) compositions based correlation / mixing lines involving assumptions about one isotopic ratio in the end-member. Some of the components established in this way are of nucleosynthetic origin and carried by presolar grains (diamond, SiC, graphite). Their isotopic compositions are testament to the nuclear processes by which elements are made in the interior of the stars around which those carrier grains formed. 

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