Chapter 7 - Noble Gases in the Earth
Published online by Cambridge University Press: 18 August 2009
Summary
Overview
In previous chapters, we have discussed noble gas characteristics in major geological divisions in the Earth, such as ocean, crust, and mantle. Differences in noble gas isotopic ratios and in relative elemental abundances among these divisions are primarily due to the addition of radio- and nucleogenic isotopes and to elemental fractionation in the course of evolution of the respective regions. An implicit assumption underlying these discussions is that the Earth was endowed with a primordial noble gas common to all the regions. Although we still do not have direct evidence to prove (or disprove) this, discussions in previous chapters and also in this chapter seem to support this assumption. A question then arises: what would be the primordial noble gas in the Earth? In this regard, we emphasize that the primordial noble gas in the Earth, especially its isotopic compositions, is a key constraint as a reference in any Earth evolution model including noble gases. Through various discussions of noble gas characteristics given in previous chapters, we have learned that the primordial noble gas in the Earth was likely to be derived from solar noble gas by some massdependent fractionation. In this chapter, especially in Sections 7.3 and 7.7, we will discuss these questions in more detail.
As already mentioned, current noble gases in the Earth have been modified by addition of radio- and nucleogenic isotopes and by elemental fractionation due to various geological processes.
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- Noble Gas Geochemistry , pp. 217 - 252Publisher: Cambridge University PressPrint publication year: 2001