Magmas fluid inclusions

D and 8 0 data on fluid inclusions and minerals at main stage of epithermal Au-Ag mineralization clearly indicate that the dominant source of ore fluids is meteoric water. Meteoric water penetrates downwards and is heated by the country rocks and/or intrusive rocks. The heated water interacts with country rocks and/or intrusive rocks and extracts sulfur, Au, Ag and other soft cations (e.g., Hg, Tl) from these rocks. If hydrothermal solution boils, it becomes neutral or slightly alkaline, leading to the selective leaching of soft cations such as Au, Ag, Hg and Tl from country rocks. However, a contribution of sulfur gas and other components from magma cannot be ruled out. 

Other geochemical characteristics of Italian volcanism are also not easily explained by the plume hypotheses. For example, deep mantle plumes are commonly associated with high 3He/4He ratios (e.g. Farley and Neroda 1998). However, measurements carried out on fluid inclusions in olivine phenocrysts from mafic Italian rocks have yielded low He isotopic ratios with R/Ra < 7.5 (e.g. Sano et al. 1989 Graham et al. 1993 Marti et al. 1994 Di Liberto 2003 Martelli et al. 2004), which are much lower than compositions found for plume-related magmas. 

Frezzotti ML, Peccerillo A (2004) Fluid inclusion and petrological studies elucidate reconstruction of magma conduits. Eos 85 157-163... 

Vaggelli G, Francalanci L, Ruggieri G, Testi S (2003) Persistent polybaric rests of calc-alkaline magmas at Stromboli volcano, Italy pressure data from fluid inclusions inrestitic quartzite nodules. Bull Volcanol 65 385-404... 

Zanon V, Frezzotti ML, Peccerillo A (2003) Magmatic feeding system and crustal magma accumulation beneath Vulcano Island (Italy) evidence from fluid inclusions in quartz xenoliths. J Geophys Res, 108, B6, 2298,... 

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. 

Hansteen T. H., Klugel A., and Schmincke H. U. (1998) Multistage magma ascent beneath the Canary Islands evidence from fluid inclusions. Contrib. Mineral. Petrol. 132,48-64. 

Muehlenbachs K, Byerly G (1982) 0 enrichment of silicic magmas caused by crystal fractionation at the Galapagos spreading center. Contrib Mineral Petrol 79 76-79 Nadeau S, Philppot P, Pineau F (1993) Fluid inclusion and mineral isotopic compositions (H-C-0) in eclogitic rocks as tracers of local fluid migration during high-pressure metamorphism. Earth Planet Sci Letters 114 431-448... 

Frezzotti ML, Peccerillo A, Bonelli R (2003) Magma ascent rates and depths of crustal magma reservoirs beneath the Aeolian volcanic arc (Italy) inferences from fluid and melt inclusions in xenoliths. In De Vivo B, Bodnar RJ (eds) Melt Inclusions in Volcanic Systems Methods, Applications and Problems. Elsevier, Amsterdam, pp 185-205... 

Table 1 Summary of typical pre-emptive volatile abundances of magmas in different tectonic settings. Note that volatiles can be contained in solution, in crystalUzed phases, and in a separate vapor phase. The values reported in the table are generally for the melt phase (dissolved) though tme bulk volatile abundances for a magma would sum all these potential reservoirs. In particular, some magmas show abundant evidence for a substantial fluid phase co-existing with the melt prior to emption, which is often not represented in melt inclusion-based estimates of...

In order to introduce inclusions, sufficient shear stress must be applied to the xenoliths within the magma to create fractures. It is not clear under what circumstances this can be done without destroying the xenolith. CO2 bubbles within the magma also must be available on the xenolith surfaces to enter propagating cracks. It is more likely that in many cases the fracturing and fluid introduction occur prior to xenolith entrainment, either immediately before xenolith entrainment, or by an earlier sequence of fluid invasion of the xenolith source region. 

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