Trace element isotope correlation

Based on major and trace element variations, it has been argued that fractional crystallisation was the dominant evolutionary mechanism for Ustica magmas (Cinque et al. 1988). The lack of correlation between silica and Sr isotopic ratios has been interpreted as evidence that assimilation of crustal rocks played a minor role during magma evolution. The variable contents of K20, P2Os incompatible elements and radiogenic Sr in the mafic rocks most likely reflect the occurrence of various types of primary melts at Ustica. 

The commonly observed correlation of isotopic and trace element indices of enrichment attests to the fact that the sub-oceanic mantle is composi-tionally heterogeneous, even in areas distant from hotspots (see, e.g.. Figure 16). One widely discussed theory suggests that the enriched-to-depleted range in MORE (and near-axis seamount) compositions results from melting of enriched... 

Figure 13 Trace-element concentrations in ppm, trace-element ratios, and isotope ratios for primitive arc lavas in our compilation. A high Ba/La, low Th/La component has Sr/ Sr 0.704, while a distinct low Ba/La, high Th/La component in most oceanic arcs has Sr/ Sr 0.706. However, continental arcs, the oceanic Aleutian arc, and some other primitive arc lavas have relatively high Ba/La and Th/La. For most oceanic arcs, Ba and Th concentration in primitive lavas are correlated (Figure 12) and both are correlated with Sr/ Sr. With very few exceptions, primitive andesites from the oceanic Aleutian arc and from continental arcs show lower Sr/ Sr and at a given Ba...

In comparison to MORBs, some OIBs show a much steeper correlation in the Ne three-isotope diagram (Fig. 11). This is especially true for the cases of Hawaii, Iceland and Reunion (Fig. 11 Honda et al. 1991 Valbracht et al. 1997 Trieloff et al. 2000 Dixon et al. 2000 Moreira et al. 2001 Hanyu et al. 2001). These steep trends reveal that these OIB mantle sources have less nucleogenic Ne (lower Ne/ Ne) than the MORB mantle source. Because MORBs also show more radiogenic He than OIBs from Hawaii, Iceland and Reunion, the mantle source for MORBs must be characterized by lower time-integrated He/(U+Th) and Ne/(U+Th) than the mantle source for those OIBs. Because the MORB mantle source is also trace element-depleted compared to the source for many OIBs, the OIB mantle source, at least for cases such as Hawaii, Iceland and Reunion, must be less degassed (i.e., it has higher He and Ne concentrations) than the upper mantle source ofMORBs. 

Since an isotope ratio cannot be fractionated by crystal-liquid equilibria and therefore is indicative of the magmatic source, the correlation between an isotope ratio and a major or trace element can be used as a guide to the major element or trace element composition of the source. Typically, ratios of highly incompatible trace elemente (Section 4.7.1 and Table 6.7) are most usehil in characterizing the... 

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