Mantle water content

Preparation and Standardisation of Alumina. The activity of alumina depends inversely on its water content, and a sample of poorly active material can be rendered more active by leaving for some time in a round bottomed flask heated up to about 200° in an oil bath or a heating mantle while a slow stream of a dry inert gas is passed through it. Alternatively, it is heated to red heat (380-400°) in an open vessel for 4-6h with... 

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). 

Small Quantities. Wear nitrile rubber gloves, laboratory coat, and eye protection. Work in the fume hood. Small quantities of hexamethylphosphoramide can be hydrolyzed with concentrated hydrochloric acid under reflux for at least 5 hours. Add 215 mL of concentrated hydrochloric acid to a 500-mL, three-necked, round-bottom flask equipped with stirrer, heating mantle, water-cooled condenser, and dropping funnel. Over a period of about 30 minutes, add 50 mL (51.5 g, 0.3 mol) of the hexamethylphosphoramide through the dropping funnel while refluxing the reaction mixture. After addition is complete, reflux the mixture for at least 5 hours. Cool the contents of the flask, neutralize carefully with dilute sodium hydroxide or sodium carbonate, and wash the resultant mixture into the drain.6... 

Surrounding the core, the mantle has a thickness of about 2900 km. Its mass is estimated at 4 x 1024 kg. It is composed mainly of high-density silicates of Mg and Fe. It is divided into three layers lower (2000 km), transition (500 km), and upper mantle (360 km). The lower mantle is predominantly formed by Mg-perovskite, Mg-wurstite, and Ca-perovskite, which contain water in their crystal structures. Incredibly as it may seem, because of this water content the lower mantle is believed to contain more water than the oceans. 

The radiation-induced conductivity in hydrated samples of aligned versus non-aligned solid DNA fibers was compared by Warman et al. [166]. The dry fibers were found to be essentially nonconducting, as a water content of 10-15 waters per base pair is necessary to observe conductivity. Under these conditions, the conductivity of the aligned and nonaligned films was found to be similar. It was concluded that conductivity in solid B-DNA is due to highly mobile charge carriers within the outer mantle of the biopolymer chains rather than within the base-pair cores. ... 

Dixon et al. (2002) take this approach one step further, and use new data on water contents, trace element and isotope geochemistry of Atlantic basalts to argue that mantle endmember reservoirs or components, previously defined on the basis of their isotope geochemistry, have different water contents. They propose that depleted MORE mantle (DMM) has 100 ppm H2O, FOZO ( focus zone component of Hart et al., 1992) has 750 ppm H2O, and enriched mantle (EM) has approximately half the H2O concentration as FOZO. 

At this point, it seems useful to review the current state of the science with respect to the major minerals of the mantle. Different authors report water contents in different ways atoms H/10 atoms Si, ppm OH, ppm H2O, etc. To ease comparison, the authors original values have been converted, where necessary, to ppm H2O. 

Aines R. D. and Rossman G. R. (1984a) The water content of mantle garnets. Geology 12, 720-723. 

Peslier A. H., Luhr J. F., and Post J. (2002) Low water contents in pyroxenes from spinel-peridotites of the oxidized, sub-arc mantle wedge. Earth Planet Sci. Lett. 201, 69-86. 

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. 

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