Magmas water content

REE patterns are fractionated for all the rocks, but tholeiites show lower La/Yb ratios than alkaline products (Fig. 8.5a). Incompatible element patterns normalised to primordial mantle compositions for mafic rocks are very different from the Aeolian arc and central-southern Italian peninsula. Both tholeiitic and alkaline basalts show a marked upward convexity, with negative spikes of K (Fig. 8.5b). Note, however, that there are also negative anomalies for Hf and Ti, which are uncommon in most Na-alkaline basalts from intraplate settings (e.g. Wilson 1989). Overall, the Etna magmas have been found to be more enriched in volatile components than common intraplate magmas, and water contents up to 3-4 wt % have been found by melt inclusion studies (Corsaro and Pompilio 2004 Pompilio, personal communication). 

My sen and Wheeler, 2000). In this regard, they would be efficient fluxing agents, causing additional melt to form via melt/rock reaction in the mantle wedge (Eiler et al., 2000). In principle, addition of such H20-rich melts to the mantle wedge could explain the substantial water contents in primitive arc magmas, without additional H2O from a fluid. 

Many trace element studies use the ratio of fluid-mobile to immobile elements such as Ba(mobile)/La(immobile) and Pb/Ce in arc magmas as a monitor of fluid transfer into the mantle wedge (see e.g. Ayers, 1998). The higher the Ba/La or Pb/Ce ratio, the greater the fluid flux. In addition, further evidence for the presence of a fluid phase in the source of arc magmas is their relatively high water content. 

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