11.2 Neon

Until recently, neon was the most problematical of the rare gases. Of its three isotopes, ²¹Ne and ²²Ne are nucleogenic and their variations are well understood. In contrast, ²⁰Ne is non nucleogenic, and the causes of its variation in the Earth were hotly debated. However, the resolution of this debate has now made neon isotopes a kind of ‘Rosetta Stone’ for understanding the behaviour of the other rare gases in mantle sources.

11.2.1 Neon production

The principal nuclear reactions which generate neon isotopes are n, " reactions on ²⁴Mg and ²⁵Mg, which produce ²¹Ne and ²²Ne respectively. Subsidiary pathways are ", n reactions on ¹⁸O and ¹⁹F which produce ²¹Ne and ²²Na, the latter undergoing $ decay to ²²Ne. The ", n reaction on ¹⁷O to yield ²⁰Ne is unimportant, due to the low abundance of the parent. All " particles are derived from the U-series decay chains, while the neutrons are mostly produced by secondary reactions from " particles.

These reactions were first studied by Wetherill (1954), and have been refined in subsequent work (e.g. Kennedy et al., 1990). The net result of these reactions is to yield a trend towards lower ²⁰Ne/²²Ne and higher ²¹Ne/²²Ne ratios which is most clearly seen in uranium-rich rocks such as granites. Figure 11.17 shows isotopic data for gas wells from Alberta, Canada, plotted on the commonly used neon three-isotope diagram. The data form a linear array which was attributed to mixing between atmospheric and nucleogenic neon. This is consistent with helium isotope data for these gases, which show a strong radiogenic signature with no mantle-derived component.

Fig. 11.17. Neon three-isotope correlation diagram showing well gases from the Alberta basin on a mixing line between atmospheric and nucleogenic neon. After Kennedy et al. (1990).

Isotopic analysis of exposed terrestrial rocks has also demonstrated the cosmogenic production of ²¹Ne (Marty and Craig, 1987). This isotope is produced by spallation reactions on Mg, Na, Si and Al, generating a sub-horizontal array on the three-isotope plot. By analysing all three isotopes, the cosmogenic component can resolved from trapped (magmatic) neon and nucleogenic neon. Graf et al. (1991) applied the cosmogenic neon method to quartz separates from Antarctic rocks which had previously been dated by ²⁶Al and ¹⁰Be (section 14.6.2). They demonstrated coherent behaviour of ²¹Ne with these other cosmogenic isotopes, suggesting that neon will be a useful tool in determining cosmic exposure ages of surficial rocks.

11.2.2 Solar neon in the Earth

The first evidence for non-atmospheric neon in the mantle was presented by Craig and Lupton (1976) from samples of MORB and volcanic gases. These are enriched in ²⁰Ne, as well as nucleogenic ²¹Ne, relative to ²²Ne contents. Subsequently, Harding County well gas was also found to have a composition well removed from atmosphere (Phinney et al., 1978). These ²⁰Ne-enriched components were attributed to exotic primordial rare gas components in the Earth, possibly representing solar neon. In contrast, Kyser and Rison (1982) speculated that ²⁰Ne enrichment in the analysed samples might be due to mass fractionation of neon from an original mantle composition similar to that of the atmosphere. They compared a compilation of mantle-derived neon analyses with neon data from geothermal gases in Japan (Nagao et al., 1979). These gases display a mass-fractionation trend (Fig. 11.18) which is explained by preferential diffusion of light neon through the soil to the sampling sites.

Fig. 11.18. Comparison of mantle samples ( ! ), and mass-fractionated geothermal gases ( " ), on a neon three-isotope diagram. After Kyser and Rison (1982).

Elevated ²⁰Ne abundances were also found in diamonds (Fig. 11.19) by Honda et al. (1987) and Ozima and Zashu (1988; 1991). These analyses disproved the ²⁰Ne ‘enrichment’ model of Kyser and Rison, since diamonds represent in situ solid samples of the mantle. Therefore, Ozima and Zashu reversed the mass fractionation argument of Kyser and Rison, suggesting that diamonds sample a solar neon reservoir in the Earth, whereas the present-day atmosphere has been depleted in ²⁰Ne by mass fractionation. They argued that bombardment of the early Earth by radiation caused the massive blow-off of a primitive solar-type atmosphere, leaving a residue enriched in heavy neon.

Fractionation of the proposed magnitude between mantle and atmosphere should be accompanied by fractionation of the non-radiogenic isotopes of argon, krypton and xenon. Therefore, it should be possible to test the atmospheric fractionation model by isotopic analysis of the heavy rare gases. However, two factors make such tests difficult to perform. Firstly, the heavier rare gases respond to fractionation effects to a lesser degree; and secondly, the heavy rare gases are more likely to be recycled back into the mantle, masking the effect of any mantle–atmosphere fractionation of such gases. This subject will be re-examined below.

Fig. 11.19. Neon isotope data for diamonds compared with the composition of other solar system components. (The solar-wind composition was determined by analysis of Lunar soil). For data sources, see text.

Additional insights into terrestrial neon systematics have been sought from the analysis of submarine basaltic glasses. Sarda et al. (1988) demonstrated the existence of a MORB correlation line passing through the atmosphere point, which has been confirmed by several subsequent studies (e.g. Marty, 1989; Hiyagon et al., 1992; Moreira et al., 1998). This array (Fig. 11.20) can be explained by three-component mixing of solar-type, atmosphere-type and nucleogenic neon, as discussed below.

Fig. 11.20. Compilation of MORB neon data ( ! ) on a 3-isotope plot. A and B represent the ‘planetary’ neon compositions seen in some meteorites. After Hiyagon (1992).

Sarda et al. (1988) also determined neon isotope ratios in several Loihi glasses which fell within error of the atmospheric composition. They believed that these signatures represented a genuine primordial mantle signature, consistent with this reservoir being the principal source of atmospheric neon. However, subsequent analyses of submarine basalt glasses from Loihi and nearby Kilauea revealed a wider range of neon isotope ratios, stretching from the atmospheric composition towards ²⁰Ne-enriched compositions (Honda et al., 1991; Hiyagon et al., 1992). The enriched end of this array approaches the solar wind composition, but the array has a slope intermediate between the pure mass-fractionation line and the MORB correlation line (Fig. 11.21). In order to explain these results, Honda et al. and Hiyagon et al. attributed all neon in the Earth’s interior to mixing between solar and nucleogenic isotopes. The sloping arrays of MORB and OIB were then attributed to variable atmospheric contamination of this solar plus radiogenic mantle neon, whereas the Loihi neon samples originally analysed by Sarda et al. (1988) were attributed almost entirely to atmospheric contamination.

Fig. 11.21. Compilation of Hawaiian neon data on a three-isotope plot. ( " ) = Loihi; ( ! ) = Kilauea. After Hiyagon et al. (1992).

Allegre et al. (1993) attempted to reinstate the ‘planetary model’ for neon in the deep mantle by invoking a new mechanism to explain high ²⁰Ne/²²Ne ratios of solar type in the earth’s mantle. They attributed these signatures to the subduction of cosmic dust particles accumulated in deep-sea sediments. These dust particles become implanted with neon from the solar wind during their exposure in space. Analysis of this material in the atmosphere and in deep sea sediment reveals ²⁰Ne/²²Ne ratios which span the range between atmospheric and solar compositions (e.g. Nier and Schlutter, 1990). Matsuda et al. (1990) suggested that these particles could survive the ‘noble gas subduction barrier’ and deliver cosmic (solar) neon to the deep mantle. This could explain the high ²⁰Ne/²²Ne ratios of submarine glasses without having to invoke solar-type primordial neon in the Earth. However, experimental studies by Hiyagon (1994) suggested that neon would be completely extracted from cosmic dust within three years at 500 ^oC, which is insufficient to sustain this model.

Ozima and Igarashi (2000) also rejected the ‘solar neon’ model. Their argument was based on the distribution of data in a histogram of ²⁰Ne/²²Ne ratios from MORB, OIB and diamonds (Fig. 11.22). They argued that since the distribution tailed away to nothing at the solar wind composition, solar neon could not be a major component of the terrestrial rare gas inventory. However, it should be noted that the tailing effect in Fig. 11.23 is mainly due to OIB data. The MORB distribution is essentially flat, indicating relatively equal mixing of solar and atmospheric neon in these samples. The distribution of OIB data in Fig. 11.23 is mainly a historical artefact, representing the great difficulties encountered in excluding atmospheric contamination in earlier work. However, improved methods to combat atmospheric contamination have gradually been developed, as seen in recent data presented by Harrison et al. (1999) while the paper by Ozima and Igarashi was under revision. These new neon isotope data from Iceland reached ²⁰Ne/²²Ne ratios above 13.5 for the first time, overlapping with the solar wind composition.

Fig. 11.22. Histogram of neon isotope data for MORB (hatched); diamonds (stipple) and OIB (clear) to show the distribution of data between the atmospheric and Solar Wind values. After Ozima and Igarashi (2000).

Further evidence from Iceland in support of the Solar Neon model was provided by Dixon et al. (2000) and Moreira et al. (2001). For the first time, these studies revealed a correlation steeper than the L–K line on the three-isotope plot, falling within error of the mass fractionation line between atmospheric and solar neon (Fig. 11.23). This discovery provides important support for the two-reservoir model for terrestrial noble gases (section 11.1.4), because it implies that the Earth does contain an essentially primordial neon reservoir.

Fig. 11.23. Neon three-isotope plot showing new Iceland data, some of which lie within error of the mass fractionation line between atmospheric and solar neon. ( ! ) = olivine; ( " ) = glass. After Dixon et al. (2000).

11.2.3 Neon and helium

Following widespread acceptance of the solar neon model for the Earth, neon and helium isotope data can now be placed in a unified model. This is because helium does not suffer significant atmospheric contamination, while atmospheric contamination of neon can be corrected using the three isotope plot. Relationships between neon and heavy rare gases will be discussed in the next section.

One way of correcting for atmospheric neon contamination is to calculate the slopes of data arrays on the three-isotope plot by forcing a regression line through the atmosphere composition. The gradient of this regression line is then equal to the ratio *²⁰Ne/*²¹Ne. Poreda and Farley (1992) used this notation to compare the neon compositions of various mantle sources, categorised according to ³He/⁴He ratio (expressed as R/R_A). The results of this analysis are presented in Fig. 11.24. In addition to data from Loihi and MORB, new data were obtained from ultramafic xenoliths from Reunion and two different localities in the Samoan islands, which were found to define neon isotope arrays with slopes intermediate between those for Hawaii and MORB (Staudacher et al., 1990; Poreda and Farley, 1992). Overall, the data suggest a correlation between neon and helium isotope ratios, which can be explained by the addition of a nucleogenic)radiogenic neon)helium component to a variably degassed primordial component.

Fig. 11.24. Correlation of neon and helium isotope signatures in mantle sources, expressed as histograms of *²⁰Ne/*²¹Ne, categorised by R/R_A ratio. Different OIB samples are distinguished by hatching. After Poreda and Farley (1992).

An alternative way of correcting for atmospheric neon contamination is to project data away from the atmosphere point to the solar ²⁰Ne/²²Ne ratio, whereupon the neon data are presented as normalised ²¹Ne/²²Ne ratios. Porcelli and Wasserburg (1995b) used this notation to compare neon and helium data for depleted mantle, lower mantle plumes, and meteorites (representing the initial Earth). These reservoirs form an approximately linear growth curve on a diagram of ²¹Ne/²²Ne against ⁴He/³He. This is consistent with the common progenitors U and Th, which produce radiogenic helium and nucleogenic neon. Porcelli and Wasserburg (1995b) also argued that the linear Ne–He growth curve is consistent with a steady state model for mantle rare gases.

The atmospheric contamination model successfully explains the neon isotope arrays in submarine glasses, but it brings us back to the problem of explaining the origin of the atmospheric neon signature itself. Most workers now support the hypothesis that neon fractionation occurred during the burn-off of an early terrestrial atmosphere of solar composition (as proposed by Ozima and Zashu, 1988; 1991). This question was re-evaluated by Pepin (1997), who argued that a giant impact in the early history of the Earth would have fractionated all rare gas isotope ratios, including those of neon and the heavy rare gases. Nevertheless, he argued that atmospheric burn-off powered by extreme ultra-violet solar radiation was still necessary to explain the observed atmospheric neon signatures. An alternative model proposed by Marty (1989) is that the atmosphere was formed by late accretion of gas-rich meteorites with planetary neon (e.g. neon A in Fig. 11.20). These could have been accreted to the surface of the Earth subsequent to the formation of the mantle with a solar neon budget.

References

Aldrich, L. T. and Nier, A. O. (1948). The occurrence of He³ in natural sources of helium. Phys. Rev. 74, 1590)4.

Allegre, C. J., Moreira, M. and Staudacher, T. (1995). ⁴He/³He dispersion and mantle convection. Geophys. Res. Lett. 22, 2325–8.

Allegre, C. J., Sarda, P. and Staudacher, T. (1993). Speculations about the cosmic origin of He and Ne in the interior of the Earth. Earth Planet. Sci. Lett. 117, 229)33.

Allegre, C. J., Staudacher, T. and Sarda, P. (1986). Rare gas systematics: formation of the atmosphere, evolution and structure of the Earth’s mantle. Earth Planet. Sci. Lett. 81, 127–50.

Allegre, C. J., Staudacher, T., Sarda, P. and Kurz, M. (1983). Constraints on evolution of Earth’s mantle from rare gas systematics. Nature 303, 762)6.

Alvarez, L. W. and Cornog, R. (1939). Helium and hydrogen of mass 3. Phys. Rev. 56, 613.

Anderson, D. L. (1993). Helium-3 from the mantle: primordial signal or cosmic dust? Science 261, 170)6.

Anderson, D. L. (2001). A statistical test of the two reservoir model for helium isotopes. Earth Planet. Sci. Lett. 193, 77–82.

Burnard, P., Graham, D. and Turner, G. (1997). Vesicle-specific noble gas analyses of "popping rock": implications for primordial noble gases in Earth. Science 276, 568–71.

Butler, W. A., Jeffery, P. M., Reynolds, J. H. and Wasserburg, G. J. (1963). Isotopic variations in terrestrial xenon. J. Geophys. Res. 68, 3283)91.

Caffee, M. W., Hudson, G. B., Velsko, C., Alexander, E. C., Huss, G. R. and Chivas, A. R. (1988). Non-atmospheric noble gases from CO₂ well gases. Lunar Planet. Sci. 19, 154–5 (abs).

Caffee, M. W., Hudson, G. B., Velsko, C., Huss, G. R., Alexander, E. C. and Chivas, A. R. (1999). Primordial noble gases from Earth’s mantle: identification of a primitive volatile component. Science 285, 2115–18.

Cerling, T. E. (1989). Dating geomorphologic surfaces using cosmogenic ³He. Quaternary. Res. 33, 148)56.

Clarke, W. B., Beg, M. A. and Craig, H. (1969). Excess ³He in the sea: evidence for terrestrial primordial helium. Earth Planet. Sci. Lett. 6, 213)20.

Clarke, W. B., Jenkins, W. J. and Top, Z. (1976). Determination of tritium by mass-spectrometric measurement of ³He. Int. J. Appl. Rad. Isot. 27, 515)22.

Coltice, N. and Ricard, Y. (1999). Geochemical observations and one layer mantle convection. Earth Planet. Sci. Lett. 174, 125–37.

Craig, H. and Lupton, J. E. (1976). Primordial neon, helium, and hydrogen in oceanic basalts. Earth Planet. Sci. Lett. 31, 369)85.

Craig, H. and Poreda, R. J. (1986). Cosmogenic ³He in terrestrial rocks: the summit lavas of Maui. Proc. Nat. Acad. Sci. USA 83, 1970)4.

Damon, P. E. and Kulp, L. (1958). Excess helium and argon in beryl and other minerals. Amer. Miner. 43, 433)59.

Dixon, E. T., Honda, M., McDougall, I., Campbell, I. H. and Sigurdsson, I. (2000). Preservation of near-solar neon isotopic ratios in Icelandic basalts. Earth Planet. Sci. Lett. 180, 309–24.

Fanale, F. P. (1971). A case for catastrophic early degassing of the Earth. Chem. Geol. 8, 79)105.

Farley, K. A. (1995a). Rapid cycling of subducted sediments into the Samoan mantle plume. Geology 23, 531–4.

Farley, K. A. (1995b). Cenozoic variations in the flux of interplanetary dust recorded by ³He in a deep-sea sediment. Nature 376, 153–6.

Farley, K. A. and Craig, H. (1994). Atmospheric argon contamination of ocean island basalt olivine phenocrysts. Geochim. Cosmochim. Acta 58, 2509)17.

Farley, K. A., Montanari, A., Shoemaker, E. M. and Shoemaker, C. S. (1998). Geochemical evidence for a comet shower in the late Eocene. Science 280, 1250–3.

Farley, K. A. and Patterson, D. B. (1995). A 100-kyr periodicity in the flux of extraterrestrial ³He to the sea floor. Nature 378, 600–3.

Farley, K. A. and Poreda, R. J. (1993). Mantle neon and atmospheric contamination. Earth Planet. Sci. Lett. 114, 325)39.

Fisher, D. E. (1971). Incorporation of Ar in East Pacific basalts. Earth Planet. Sci. Lett. 12, 321)4.

Fisher, D. E. (1983). Rare gases from the undepleted mantle? Nature 305, 298)300.

Fisher, D. E. (1985). Noble gases from oceanic island basalts do not require an undepleted mantle source. Nature 316, 716)18.

Fisher, D. E. (1986). Rare gas abundances in MORB. Geochim. Cosmochim. Acta 50, 2531)41.

Gerling, E. K., Mamyrin, B. A., Tolstikhin, I. N. and Yakovleva, S. S. (1971). Isotope composition of helium in some rocks. Geokhimiya 10, 1209)17.

Graf, T., Kohl, C. P., Marti, K. and Nishiizumi, K. (1991). Cosmic-ray-produced neon in Antarctic rocks. Geophys. Res. Lett. 18, 203)6.

Graham, D. W., Castillo, P. R., Lupton, J. E. and Batiza, R. (1996). Correlated He and Sr isotope ratios in South Atlantic near-ridge seamounts and implications for mantle dynamics. Earth Planet. Sci. Lett. 144, 491–503.

Hanyu, T. and Kaneoka, I. (1997). The uniform and low ³He/⁴He ratios of HIMU basalts as evidence for their origin as recycled materials. Nature 390, 273–6.

Harrison, D., Burnard, P. and Turner, G. (1999). Noble gas behaviour and composition in the mantle: constraints from the Iceland Plume. Earth Planet. Sci. Lett. 171, 199–207.

Hart, R., Dymond, J. and Hogan, L. (1979). Preferential formation of the atmosphere)sialic crust system from the upper mantle. Nature 278, 156)9.

Hart, R., Dymond, J., Hogan, L. and Schilling, J. G. (1983). Mantle plume noble gas component in glassy basalts from Reykjanes Ridge. Nature 305, 403)7.

Hart, R., Hogan, L. and Dymond, J. (1985). The closed-system approximation for evolution of argon and helium in the mantle, crust and atmosphere. Chem. Geol. (Isot. Geosci. Sect.) 52, 45)73.

Hennecke, E. W. and Manuel, O. K. (1975). Noble gases in CO₂ well gas, Harding County, New Mexico. Earth Planet. Sci. Lett. 27, 346)55.

Hilton, D. R., Barling, J. and Wheller, G. E. (1995). Effect of shallow-level contamination on the isotope systematics of ocean-island lavas. Nature 373, 330–3.

Hilton, D. R., Gronvold, K, Macpherson, C. G. and Castillo, P. R. (1999). Extreme ³He/⁴He ratios in northwest Iceland: constraining the common component in mantle plumes. Earth Planet. Sci. Lett. 173, 53–60.

Hilton, D. R., Hammerschmidt, K., Loock, G. and Friedrichsen, H. (1993a). Helium and argon isotope systematics of the central Lau Basin and Valu Fa Ridge: evidence of crust/mantle interactions in a back-arc basin. Geochim. Cosmochim. Acta 57, 2819–41.

Hilton, D. R., Hammerschmidt, K., Teufel, S. and Friedrichsen, H. (1993b). Helium isotope characteristics of Andean geothermal fluids and lavas. Earth Planet. Sci. Lett. 120, 265–82.

Hilton, D. R., Thirlwall, M. F., Taylor, R. N., Murton, B. J. and Nichols, A. (2000). Controls on magmatic degassing along the Reykjanes Ridge with implications for the helium paradox. Earth Planet. Sci. Lett. 183, 43–50.

Hiyagon, H. (1994). Retention of solar helium and neon in IDPs in deep sea sediment. Science 263, 1257)9.

Hiyagon, H., Ozima, M., Marty, B., Zashu, S. and Sakai, H. (1992). Noble gases in submarine glasses from mid-ocean ridges and Loihi seamount: constraints on the early history of the Earth. Geochim. Cosmochim. Acta 56, 1301)16.

Hoke, L., Hilton, D. R., Lamb, S. H., Hammerschmidt, K. and Friedrichsen, H. (1994). ³He evidence for a wide zone of active mantle melting beneath the Central Andes. Earth Planet. Sci. Lett. 128, 341–55.

Honda, M., Reynolds, J. H., Roedder, E. and Epstein, S. (1987). Noble gases in diamonds: occurrences of solar-like helium and neon. J. Geophys. Res. 92, 12507)21.

Jacobsen, S. B. and Harper, C. L. (1996). Accretion and early differentiation history of the Earth based on extinct radionuclides. In: Basu, A. and Hart, S. R. (Eds.), Earth Processes: Reading the Isotopic Code. Geophys. Monograph 95, pp. 47–74.

Jambon, A. and Zimmermann, J. L. (1987). Major volatiles from an Atlantic MORB glass: a size fraction analysis. Chem. Geol. 62, 177)89.

Jeffrey, P. M. and Hagan, P. J. (1969). Negative muons and the isotopic composition of the rare gases in the Earth’s atmosphere. Nature 223, 1253.

Jephcoat, A. P. (1998). Rare-gas solids in the Earth's deep interior. Nature 393, 355–8.

Honda, M., McDougall, I., Patterson, D. B., Doulgeris, A. and Clague, D. A. (1991). Possible solar noble-gas component in Hawaiian basalts. Nature 349, 149)51.

Kaneoka, I. and Takaoka, N. (1980). Rare gas isotopes in Hawaiian ultramafic nodules and volcanic rocks: constraints on genetic relationships. Science 208, 1366–8.

Kellog, L. H. and Wasserburg, G. J. (1990). The role of plumes in mantle helium fluxes. Earth Planet. Sci. Lett. 99, 276–89.

Kennedy, B. M., Hiyagon, H. and Reynolds, J. H. (1990). Crustal neon: a striking uniformity. Earth Planet. Sci. Lett. 98, 277)86.

Kortenkamp, S. J. and Dermott, S. F. (1998). a 100,000-year periodicity in the accretion rate of interplanetary dust. Science 280, 874–6.

Kunz, J. (1999). Is there solar argon in the Earth’s mantle? Nature 399, 649–50.

Kunz, J., Staudacher, T. and Allegre, C. J. (1998). Plutonium-fission xenon found in the Earth’s mantle. Science 280, 877–80.

Kunz, W. and Schintlmeister, I. (1965). Tabellen der Atomkerne, Teil II, Kernreaktionen. Akademie-Verlag, 1022 p.

Kuroda, P. K. (1960). Nuclear fission in the early history of the Earth. Nature 187, 36)8.

Kurz, M. D. (1986a). Cosmogenic helium in a terrestrial igneous rock. Nature 320, 435)9.

Kurz, M. D. (1986b). In-situ production of terrestrial cosmogenic helium and some applications to geochronology. Geochim. Cosmochim. Acta 50, 2855)62.

Kurz, M. D., Gurney, J. J., Jenkins, W. J. and Lott, D. E. (1987). Helium isotopic variability within single diamonds from the Orapa kimberlite pipe. Earth Planet. Sci. Lett. 86, 57)68.

Kurz, M. D. and Jenkins, W. J. (1981). The distribution of helium in oceanic basalt glasses. Earth Planet. Sci. Lett. 53, 41)54.

Kurz, M. D., Jenkins, W. J. and Hart, S. R. (1982). Helium isotopic systematics of oceanic islands and mantle heterogeneity. Nature 297, 43)6.

Kurz, M. D., Meyer, P. S. and Sigurdsson, H. (1985). Helium isotopic systematics within the neovolcanic zones of Iceland. Earth Planet. Sci. Lett. 74, 291)305.

Kyser, T. K. and Rison, W. (1982). Systematics of rare gas isotopes in basic lavas and ultramafic xenoliths. J. Geophys. Res. 87, 5611)30.

Lal, D. (1987). Production of ³He in terrestrial rocks. Chem. Geol. (Isot. Geosci. Sect.) 66, 89)98.

Lal, D., Nishiizumi, K., Klein, J., Middleton, R. and Craig, H. (1987). Cosmogenic ¹⁰Be in Zaire alluvial diamonds: implications to ³He excess in diamonds. Nature 328, 139)41.

Lupton, J. E., (1983). Terrestrial inert gases: isotope tracer studies and clues to primordial components in the mantle. Ann. Rev. Earth Planet. Sci. 11, 371)414.

Lupton, J. E. and Craig. H. (1975). Excess ³He in oceanic basalts: evidence for terrestrial primordial helium. Earth Planet. Sci. Lett. 26, 133)9.

Mamyrin, B. A., Anufriyev, G. S., Kamenskiy, I. L. and Tolstikhin, I. N. (1970). Determination of the composition of atmospheric helium. Geochem. Int. 7, 498)505.

Mamyrin, B. A. and Tolstikhin, I. N. (1984). Helium Isotopes in Nature. Elsevier, 273 p.

Mamyrin, B. A., Tolstikhin, I. N., Anufriyev, G. S. and Kamenskiy, I. L. (1969). Anomalous isotopic composition of helium in volcanic gases. Dokl. Akad. Nauka SSSR 184, 1197)9.

Mamyrin, B. A., Tolstikhin, I. N. Anufriyev, G. S. and Kamenskiy, I. L. (1972). Isotopic composition of helium in Icelandic hot springs. Geokhimiya 11, 1396.

Marcantonio, F., Anderson, R. F., Stute, M., Kumar, N., Schlosser, P. and Mix, A. (1996). Extraterrestrial ³He as a tracer of marine sediment transport and accumulation. Nature 383, 705–7.

Marcantonio, F., Kumar, N., Stute, M., Anderson, R. F., Seidl, M. A., Schlosser, P. and Mix, A. (1995). A comparative study of accumulation rates derived by He and Th isotope analysis of marine sediments. Earth Planet. Sci. Lett. 133, 549–55.

Marcantonio, F., Turekian, K. K., Higgins, S., Anderson, R. F., Stute, M. and Schlosser, P. (1999). The accretion rate of extraterrestrial ³He based on the oceanic ²³⁰Th flux and the relation to os isotope variation over the past 200,000 years in an Indian Ocean core. Earth Planet. Sci. Lett. 170, 157–68.

Martel, D. J., Deak, J., Dovenyi, P., Horvath, F., O’Nions, R. K., Oxburgh, E. R., Stegena, L. and Stute, M. (1989). Leakage of helium from the Pannonian basin. Nature 342, 908)12.

Marti, K. and Craig, H. (1987). Cosmic-ray-produced neon and helium in the summit lavas of Maui. Nature 325, 335)7.

Marty, B. (1989). Neon and xenon isotopes in MORB: implications for the Earth)atmosphere evolution. Earth Planet. Sci. Lett. 94, 45)56.

Marty, B. and Jambon, A. (1987). C/³He in volatile fluxes from the solid Earth: implications for carbon geodynamics. Earth Planet. Sci. Lett. 83, 16)26.

Marty, B., Tolstikhin, I., Kamensky, I. L., Nivin, V., Balaganskaya, E. and Zimmermann, J.-L. (1998). Plume-derived rare gases in 380 Ma carbonatites from the Kola region (Russia) and the argon isotopic composition in the deep mantle. Earth Planet. Sci. Lett. 164, 179–192.

Matsuda, J., Murota, M. and Nagao, K. (1990). He and Ne isotopic studies on the extraterrestrial material in deep-sea sediments. J. Geophys. Res. 95, 7111)17.

Matsuda, J., Sudo, M., Ozima, M., Ito, K., Ohtaka, O. and Ito, E. (1993). Noble gas partitioning between metal and silicate under high pressures. Science 259, 788)90.

Merrihue, C. (1964). Rare gas evidence for cosmogenic dust in modern Pacific red clay. Ann. N. Y. Acad. Sci. 119, 351)67.

Meshik, A. P., Shukolyukov, Y. A. and Je$berger, E. K. (1995). Chemically fractionated fission xenon (CFF-Xe) on the Earth and in meteorites. In: Busso, M. et al. (Eds), Nuclei in the Cosmos III, Amer. Inst. Phys. Conf. Proc. 327, 603–6.

Moreira, M., Breddam, K., Curtice, J. and Kurz, M. D. (2001). Solar neon in the Icelandic mantle: new evidence for an undegassed lower mantle. Earth Planet. Sci. Lett. 185, 15–23.

Moreira, M., Kunz, J. and Allegre, C. J. (1998). Rare gas systematics in popping rock: isotopic and elemental compositions in the upper mantle. Science 279, 1178–81.

Morrison, P. and Pine, J. (1955). Radiogenic origin of the helium isotopes in rocks. Ann. N. Y. Acad. Sci. 62, 69)92.

Mukhopadhyay, S., Farley, K. A. and Montanari, A. (2001). A 35 Myr record of helium in pelagic limestones from Italy: implications for interplanetary dust accretion from the early Maastrichtian to the middle Eocene. Geochim. Cosmochim. Acta 65, 653–69.

Muller, R. A. and Macdonald, G. J. (1995). Glacial cycles and orbital inclination. Nature 377, 107–8.

Muller, R. A. and Macdonald, G. J. (1997). Glacial cycles and astronomical forcing. Science 277, 215–18.

Nagao, K., Takaoka, N. and Matsubayashi, O. (1979). Isotopic anomalies of rare gases in the Nigorikawa geothermal area, Hokkaido, Japan. Earth Planet. Sci. Lett. 44, 82)90.

Niedermann, S., Bach, W. and Erzinger, J. (1997). Noble gas evidence for a lower mantle component in MORBs from the southern East Pacific Rise: decoupling of helium and neon isotope systematics. Geochim. Cosmochim. Acta 61, 2697–715.

Nier, A. O. and Schlutter, D. J. (1990). Helium and neon isotopes in stratospheric particles. Meteoritics 25, 263)7.

O’Nions, R. K. and Oxburgh, E. R. (1983). Heat and helium in the Earth. Nature 306, 429)36.

O’Nions, R. K. and Oxburgh, E. R. (1988). Helium volatile fluxes and the development of continental crust. Earth Planet. Sci. Lett. 90, 331)47.

O’Nions, R. K. and Tolstikhin, I. N. (1994). Behaviour and residence times of lithophile and rare gas tracers in the upper mantle. Earth Planet. Sci. Lett. 124, 131–8.

Oxburgh, E. R., O’Nions, R. K. and Hill, R. I. (1986). Helium isotopes in sedimentary basins. Nature 324, 632)5.

Ozima, M. and Igarashi, G. (1989). Terrestrial noble gases: constraints and implications on atmospheric evolution. In: Atreya, S. K., Pollack, J. B. and Matthews, M. (Eds.) Origin and Evolution of Planetary and Satellite Atmospheres. Univ. Arizona Press, pp. 306–27.

Ozima, M. and Igarashi, G. (2000). The primordial noble gases in the Earth: a key constraint on Earth evolution models. Earth Planet. Sci. Lett. 176, 219–32.

Ozima, M., Podosek, F. A. and Igarashi, G. (1985). Terrestrial xenon isotope constraints on the early history of the Earth. Nature 315, 471)4.

Ozima, M. and Zashu, S. (1983). Primitive helium in diamonds. Science 219, 1067)8.

Ozima, M. and Zashu, S. (1988). Solar-type Ne in Zaire cubic diamonds. Geochim. Cosmochim. Acta 52, 19)25.

Ozima, M. and Zashu, S. (1991). Noble gas state of the ancient mantle as deduced from noble gases in coated diamonds. Earth Planet. Sci. Lett. 105, 13)27.

Patterson, D. B. and Farley, K. A. (1998). Extraterrestrial ³He in seafloor sediments: evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust, orbital parameters, and Quaternary climate. Geochim. Cosmochim. Acta 62, 3669–82.

Patterson, D. B., Honda, M. and McDougall, I. (1990). Atmospheric contamination: a possible source for heavy noble gases in basalts from Loihi Seamount, Hawaii. Geophys. Res. Lett. 17, 705)8.

Pepin, R. O. (1991). On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icarus 92, 2–79.

Pepin, R. O. (1997). Evolution of Earth’s noble gases: consequences of assuming hydrodynamic loss driven by giant impact. Icarus 126, 148–56.

Pepin, R. O. (1998). Isotopic evidence for a solar argon component in the Earth’s mantle. Nature 394, 664–7.

Pepin, R. O. and Signer, P. (1965). Primordial rare gases in meteorites. Science 149, 253)65.

Phinney, D., Tennyson, J. and Frick, U. (1978). Xenon in CO₂ well gas revisited. J. Geophys. Res. 83, 2313)19.

Porcelli, D. and Halliday, A. N. (2001). The core as a possible source of mantle helium. Earth Planet. Sci. Lett. 192, 45–56.

Porcelli, D. and Wasserburg, G. J. (1995a). Mass transfer of xenon through a steady-state upper mantle. Geochim. Cosmochim. Acta 59, 1991–2007.

Porcelli, D. and Wasserburg, G. J. (1995b). Mass transfer of helium, neon, argon, and xenon through a steady-state upper mantle. Geochim. Cosmochim. Acta 59, 4921–37.

Poreda, R. J. and Farley, K. A. (1992). Rare gases in Samoan xenoliths. Earth Planet. Sci. Lett. 113, 129)44.

Reynolds, J. H. (1960). Determination of the age of the elements. Phys. Rev. Lett. 4, 8)10.

Reynolds, J. H. (1963). Xenology. J. Geophys. Res. 68, 2939)56.

Rutherford, E. (1906). The production of helium from radium and the transformation of matter. In: Rutherford, E., Radioactive Transformations. Yale Univ. Press, pp. 187)93.

Sarda, P., Staudacher, T. and Allegre, C. J. (1988). Neon isotopes in submarine basalts. Earth Planet. Sci. Lett. 91, 73)88.

Sarda, P., Staudacher, T., Allegre, C. J. and Lecomte, A. (1993). Cosmogenic neon and helium at Reunion: measurement of erosion rate. Earth Planet. Sci. Lett. 119, 405)17.

Sasada, T., Hiyagon, H., Bell, K. and Ebihara, M. (1997). Mantle-derived noble gases in carbonatites. Geochim. Cosmochim. Acta 61, 4219–28.

Schmalzl, J., Houseman, G. A. and Hansen, U. (1995). Mixing properties of 3-dimensional (3-D) stationary convection. Phys. Fluids 7, 1027–33.

Schwartzman, D. W. (1973). Argon degassing models of the Earth. Nature Phys. Sci. 245, 20)1.

Seta, A., Matsumoto, T. and Matsuda, J.-I. (2001). Concurrent evolution of ³He/⁴He ratio in the Earth’s mantle reservoirs for the first 2 Ga. Earth Planet. Sci. Lett. 188, 211–19.

Sheldon, W. R. and Kern, J. W. (1972). Atmospheric helium and geomagnetic field reversals. J. Geophys. Res. 77, 6194)201.

Staudacher, T. (1987). Upper mantle origin for Harding County well gases. Nature 325, 605)7.

Staudacher, T. and Allegre, C. J. (1982). Terrestrial xenology. Earth Planet. Sci. Lett. 60, 389)406.

Staudacher, T. and Allegre, C. J. (1988). Recycling of oceanic crust and sediments: the noble gas subduction barrier. Earth Planet. Sci. Lett. 89, 173)83.

Staudacher, T., Kurz, M. D. and Allegre, C. J. (1986). New noble-gas data on glass samples from Loihi Seamount and Hualalai and on dunite samples from Loihi and Reunion Island. Chem. Geol. 56, 193)205.

Staudacher, T., Sarda, P. and Allegre, C. J. (1990). Noble gas systematics of Reunion Island, Indian Ocean. Chem. Geol. 89, 1)17.

Staudacher, T., Sarda, P., Richardson, S. H., Allegre, C. J., Sagna, I. and Dmitriev, L. V. (1989). Noble gases in basalt glasses from a Mid-Atlantic Ridge topographic high at 14 ^oN: geodynamic consequences. Earth Planet. Sci. Lett. 96, 119)33.

Takayanagi, M. and Ozima, M. (1987). Temporal variation of ³He/⁴He ratio recorded in deep-sea sediment cores. J. Geophys. Res. 92, 12 531–8.

Tolstikhin, I. N., Mamyrin, B. A., Khabarin, L. V. and Erlikh, E. N. (1974). Isotopic composition of helium in ultrabasic xenoliths from volcanic rocks of Kamchatka. Earth Planet. Sci. Lett. 22, 75)84.

Tolstikhin, I. N. and O’Nions, R. K. (1996). Some comments on isotopic structure of terrestrial xenon. Chem. Geol. 129, 185–99.

Trieloff, M., Kunz, J., Clague, D. A., Harrison, D. and Allegre, C. J. (2000). The nature of pristine noble gases in mantle plumes. Science 288, 1036–8.

Turekian, K. K. (1964). Outgassing of argon and helium from the Earth. In: Brancazio, P. and Cameron, A. G. W. (Eds), The Origin and Evolution of Atmospheres and Oceans. Wiley, pp. 74)83.

Valbracht, P. J., Staudacher, T., Malahoff, A. and Allegre, C. J. (1997). Noble gas systematics of deep rift zone glasses from Loihi Seamount, Hawaii. Earth Planet. Sci. Lett. 150, 399–411.

van Keken, P. E. and Ballentine, C. J. (1998). Whole-mantle versus layered mantle convection and the role of a high-viscosity lower mantle in terrestrial volatile evolution. Earth Planet. Sci. Lett. 156, 19–32.

van Keken, P. E. and Ballentine, C. J. (1999). Dynamical models of mantle volatile evolution and the role of phase transitions and temperature-dependent rheology. J. Geophys. Res. 104, 7137–51.

Wernicke, R. S. and Lippolt, H. J. (1993). Botryoidal hematite from the Schwarzwald (Germany): heterogeneous uranium distributions and their bearing on the helium dating method. Earth Planet. Sci. Lett. 114, 287)300.

Wetherill, G. W. (1953). Spontaneous fission yields from uranium and thorium. Phys. Rev. 82, 907)12.

Wetherill, G. W. (1954). Variations in the isotopic abundances of neon and argon extracted from radioactive materials. Phys. Rev. 96, 679)83.

Zadnik, M. G., Smith, C. B., Ott, U. and Begemann, F. (1987). Crushing of a terrestrial diamond: ³He/⁴He higher than solar meteorites. Meteoritics 22, 540)1.