Geochemical variations, among

WORLDWIDE GEOCHEMICAL VARIATIONS AMONG OCEAN RIDGE BASALTS... 

Worldwide Geochemical Variations among Ocean Ridge Basalts... 

The significant relative mass difference (c. 16%) between the two stable isotopes of Li (approximately Li 7.5%, Li 92.5%), coupled with broad elemental dispersion in Earth and planetary materials, makes this a system of considerable interest in fingerprinting geochemical processes, determining mass balances, and in thermometry. Natural mass fractionation in this system is responsible for c. 6% variation among materials examined to date (Fig. 1). Although the modem era of Li isotope quantification has begun, there are still many questions about the Li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered (e.g., Hoefs 1997). 

Measurement of oxygen isotopic variations in coral heads up to 500 yr old has to be counted among the great success of the geochemical approach to paleoclimate research (Figure 2). These records have become important paleocli-matic archives of tropical climate change, and they... 

The subtle variations in ionic radius among the trivalent lanthanides, coupled with the variable oxidation state of Eu have made these elements of unique interest to students of terrestrial igneous rocks. A wide variety of patterns, which are in general quite distinctive for differing rock types, are found. In all these cases, there is a clear separation between the geochemical behaviour of Sc, which typically enters early crystallising pyroxene phases, and that of yttrium and the lanthanides. The discussion in the rest of this section concentrates on the latter. 

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