Basalts melt inclusions

Consider Ca in a basaltic melt inclusion concentric with the host mineral olivine. The radius of the inclusion is SOfim. The olivine radius is 1 mm. The Ca partition... 

Thomas JB, Bodnar RJ, Shimizu N, Sinha AK (2002) Determination of zircon/melt trace element partition coefficients from SIMS analysis of melt inclusions in zircon. Geochim Cosmochim Acta 66 2887-2901 Thompson GM, Malpas J (2000) Mineral/melt partition coefficients of oceanic alkali basalts determined on natural samples using laser ablation-inductively eouple plasma-mass spectrometry (LAM-ICP-MS). Mineral Mag 64 85-94... 

De Astis et al. (2000) and Calanchi et al. (2002b) noticed that calc-alkaline and HKCA basalts at Vulcano and Panarea have distinct trace element ratios (e.g. La/U, Rb/Zr, Zr/Nb) compared to the associated sho-shonitic and KS mafic volcanics. However, the rocks of the Calabro-Peloritano basement underlying the Aeolian volcanoes show compositions that resemble the calc-alkaline rather than shoshonitic and KS rocks this was interpreted to exclude a derivation of potassic rocks from calc-alkaline parents via crustal assimilation. The same conclusion was drawn by Frez-zotti et al. (2004), who modelled magma contamination processes using melt inclusions entrapped in metamorphic xenoliths as contaminants. 

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). 

Saal A. E., Hart S. R., ShimizuN., Hauri E. H., and Layne G. D. (1998) Pb isotopic variability in melt inclusions from oceanic island basalts, Polynesia. Science 282, 1481-1484. 

Shimizu N., Sobolev A. V., Layne G. D., and Tsameryan O. P. (2003) Large Pb isotope variations in olivine-hosted melt inclusions in a basalt fromt the Mid-Atlantic Ridge. Science (ms. submitted May 2003). 

With these caveats in mind, measured water contents of MORBs range from 0.05 wt.% to 1.40 wt.% (Figure 1) in a skewed distribution with a mean of —0.33 wt.%. Of the 328 analyses shown in Figure 1, 95% have <0.65 wt.% H2O. These results are corroborated by studies of melt inclusions in phenocrysts from MORBs. Sobolev and Chaussidon (1996) found H2O contents of 0.07-0.66 wt.%, with enriched mid-ocean ridge basalts (E-MORBs) having consistently higher H2O contents (0.34-0.66 wt.%) compared to normal mid-ocean ridge basalts (N-MORBs) (0.07-0.19 wt.%). 

Sisson and Layne (1993) analyzed melt inclusions in olivines in samples from four arc volcanoes. Inclusions in olivines in basalts from the 1974 eruption of Fuego volcano, Guatemala, contain 2.1-4.6 wt.% H2O. Inclusions in olivines in basaltic andesites from the same eruption have a wider range, from 1.0 wt.% to 6.2 wt.% H2O. Inclusions hosted in olivines in basalts from three centers in the Southern Cascades have lower water contents, ranging from 0.2 wt.% to 1.4 wt.%H20. 

Sobolev and Chaussidon (1996) summarize an extensive body of data on olivine-hosted melt inclusions from basalts from a variety of tectonic settings. They concentrated on inclusions hosted in magnesium-rich olivines, with the... 

Jambon A., Lussiez P., Clocchiatti R., Weisz J., and Hernandez J. (1992) Olivine growth rates in a tholeiitic basalt-an experimental study of melt inclusions in plagioclase. Chem. Geol. 96, 277-287. 

Shimizu N. (1998) The geochemistry of olivine-hosted melt inclusions in a FAMOUS basalt ALV519-4-1. Phys. Earth Planet. Inter. 107, 183-201. 

FIGURE 3.6 A summary diagram showing the relative contributions of ophiolites, mantle xenoliths, diamond inclusions, and basaltic melts to our knowledge of the nature of the upper and lower mantle. 

Although shallow-mantle xenoliths, hosted in alkali basalts, commonly contain C02-rich fluid inclusions (see below), there have been no reports, to the author s knowledge, of H20-rich fluid inclusions in these samples. The C02-rich fluid inclusions are commonly attributed to late, possibly magma-derived, metasomatism of the samples. If such metasomatism was produced by silicate- or carbonate-rich melts, ascent of such a melt could produce saturation in a C02-rich vapor, but H2O would partition strongly into either residual melt or hydrous phases such as phlogopite or amphibole. Thus, the absence of H2O in the fluid inclusions in these samples cannot be taken as evidence that the metasomatic agent was anhydrous. 

Shallow-mantle xenoliths, hosted in alkali basalts, commonly contain C02-rich fluid inclusions (e.g., Roedder, 1965, 1984 Frey and Prinz, 1978 Murck eta/., 1978 Miller and Richter, 1982 Pasteris, 1987 Frezzotti et al., 1994 Bumard et al., 1998 Ertan and Leeman, 1999 Andersen and Neumann, 2001). In most cases, these fluid inclusions are related to metasomatic processes to which the samples were subjected. As outlined previously, the C02-rich nature of these inclusions may be a natural consequence of degassing from an ascending melt that contains both H2O and CO2, because the greater solubility of H2O in sihcate melts would allow it to remain in solution in the residual melt. Alternatively, as proposed by Andersen and Neumann (2001), the high CO2 content in these inclusions could be the result of removal of water via reactions between the original fluid and the host mineral surrounding the inclusion. 

Schiano P., Clocchiatti R., and Joron J. L. (1992) Melt and fluid inclusions in basalts and xenoliths from Tahaa Island, Society archipelago evidence for a metasomatized upper mantle. Earth Planet. Sci. Lett. Ill, 69—82. 

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