Magmas analytical techniques

A maximum absolute age deficit of 0.108 Ma is reached when the / factor approaches zero (Figure 31.16). Therefore, even if an extremely sensitive analytical technique is available, this means that ages, for example, younger than 0.5 Ma, would be significantly corrected when/is very low. In addition, this correction is based on the assumption that all the studied domains of the zircons were in equilibrium with the same magma, which is obviously not always true. Furthermore, the whole rock analysis must be representative of the magma. 

Recently Sharp et al. (2007) have questioned the findings of Magenheim et al. (1995). Sharp et al. (2007) found that the large differences between mantle and crustal material do not exist and that the mantle and the crust have very similar isotopic composition. A possible explanation for this apparent discrepancy might be related to analytical artifacts of the TIMS technique (Sharp et al. 2007). Bonifacie et al. (2008) also observed small Cl-isotope variations only in mantle derived rocks. They demonstrated that 5 Cl values correlate with chlorine concentrations Cl-poor basalts have low S Cl values and represent the composition of uncontaminated mantle derived magmas, whereas Cl-rich basalts are enriched in Cl and are contaminated by Cl-rich material such as ocean water. 

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