Helium mantle fluxes

Naughton, J. J., Lee, J. H., Keeling, D., Finlayson, J. B., Dority, Helium flux from the earth s mantle as estimated from Hawaiian fumarolic degassing, Science, 180, 55-57 (1973). 

The imbalance between heat flow and 4He flux can also be seen from the consideration of a uranium inventory in the Earth. O Nions and Oxburgh (1983) pointed out that even though a reasonable geochemical model with 5ppb of U (K/U = 104, Th/U = 3.8) for the upper mantle can approximately account for the observed helium flux, it will yield only 3% of the observed heat flux at ridges. This result indicates that the remaining 97% of the heat flow must come from somewhere other than the upper mantle, namely either from the lower mantle or from the core or from both, whereas little extraneous 4He flux is required. This led O Nions and Oxburgh to conclude that 4He flux from the lower mantle is essentially inhibited. 

To explain the imbalance, O Nions and Oxburgh (1983) and Oxburgh and O Nions (1987) proposed that a barrier, which is suggested to exist between the upper and the lower mantle from seismic observation, has trapped helium in the lower mantle and retarded the heat transport from the lower mantle to the upper mantle. O Nions et al. (1983) suggested, from a semiquantitative discussion, that delayed heat transfer from the lower mantle to the upper mantle with a time constant of about 2Ga would enhance the present heat flow by a factor of two. McKenzie and Richter (1981) made numerical calculation on a two-layered mantle convection and showed that heat transfer from the lower mantle to the upper mantle is considerably retarded to give rise to an enhancement of the present surface heat flow up to a factor of two. If the thermal barrier not only retards the heat transfer and hence enhances the present surface heat flow but also essentially prevents the 4He flux from the lower to the upper mantle, this would qualitatively explain the imbalance. If this indeed were the case, we would expect a large amount of 4He accumulation in the lower mantle. However, it is difficult to conclude such a large accumulation of 4He in the lower mantle from the currently available scarce noble gas data derived from mantle-derived materials. 

Igarashi, G., Ozima, M., Ishibashi, I, Gamo, T., Sakai, H., Nojiri, Y., Kawai, T. (1992) Mantle helium flux from the bottom of Lake Mashu, Japan. Earth Planet. Sci. Lett., 108, 11-18. 

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

Stute, M., Sonntag, C., Deak, J., Schlosser, P. (1992) Helium in deep circulating ground water in the Great Hungarian Plain Flow dynamics and crustal and mantle helium flux. Geochim. Cosmochim. Acta, 56, 2051-67. 

Figure 6 A range of mantle models for the distribution and fluxes of noble gases in the Earth. Layered mantle models with the atmosphere derived from the upper mantle involve either progressive unidirectional depletion of the upper mantle (A) or an upper mantle subject to inputs from subduction and the deeper mantle, and has steady state concentrations (B). Whole mantle convection models involve degassing of the entire mantle, with helium with high He/ He ratios found in OIB stored in either a deep variable-thickness layer (C), a layer of subducted material at the core-mantle boundary (D), or the core (E). The models are discussed in the text and Chapter 2.06 (source Porcelli and...

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