Noble gases in the mantle

The specific model for Earth formation is the crucial assumption in this absorption scenario. If Earth formation proceeded in nebula-free space as was originally postulated by Safronov (1969) and henceforth advocated by various researchers (e.g., Levy Lunine, 1993), the absorption scenario must be abandoned. Also, the Mizuno model predicts that Ne as well as other noble gases in the mantle should have solar noble gas isotopic compositions. However, as we discussed in Chapter 5, the currently available observational data on mantle noble gases show nonsolar isotopic compositions, arguing against the Mizuno model. 

Martian mantle noble gases. Martian meteorites contain components other than those derived directly from the atmosphere (see detailed discussion by Swindle (2002)). Information on the relative abundances of the heavier noble gases in the mantle (Ott, 1988 Mathew and Marti, 2001) suggests that the " Kr/ Xe ratio is at least 10 times lower than both the martian atmosphere and the solar composition. If this is truly a source feature, it indicates that heavy noble gases trapped within the planet suffered substantially different elemental fractionation than the atmosphere (see Chapter 4.12) and have not subsequently formed a dominant fraction of the atmosphere. However, it is not possible at present to conclusively determine whether the measured elemental abundance ratios reflect an interior reservoir that was initially different from atmospheric noble gases, rather than due either to planetary processing or transport and incorporation into the samples. 

Evidence from the noble gases Ozima and Igarashi (2000) found that noble gas ratios in the upper mantle are similar to those in the modern atmosphere. This means that the noble gases in the mantle and the atmosphere experienced the same fractionation event, an event which must have taken place before the formation of the Earth, in which case the fractionation may have taken place during chondrite formation or be an even older process within the solar nebula. 

The constraints provided by Xe isotopes indicate that the noble gases in the mantle cannot have evolved in a single depleting mantle reservoir (see Xe isotopes and a nonresidual upper mantle section). Therefore, other reservoirs must be invoked to... 

Mantle Ar and Xe nonradiogenic isotope compositions. It is still an open question whether there are solar or fractionated heavy noble gases in the mantle. 

Noble gases in the mantle are trapped in minerals and, without magma generation... 

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