Water content of granitic melts from Cornwall and Erzgebirge: A Raman spectroscopy study of melt inclusions AXEL MÜLLER 1, *, RAINER THOMAS 2 ,MICHAEL WIEDENBECK 2 ,REIMAR SELTMANN 1 and KAREL BREITER 3 1 Natural History Museum, Department of Mineralogy, Cromwell Road, London SW7 5BD, UK *Corresponding author, present address: Norges geologiske undersøkelse, 7491 Trondheim, Norway, e-mail: Axel.Muller@ngu.no 2 GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany 3 Czech Geological Survey Prague, Geologicka 6, 15200 Prague 5, Czech Republic Abstract: Melt inclusions (MIs) occurring in quartz of late-Variscan Sn-specialized granites from the Land’s End pluton in SW England and from the eastern Erzgebirge volcano-plutonic complex in Germany were analyzed by Raman spectroscopy, secondary ion mass spectrometry and electron microprobe. Crystallized MIs were homogenized using cold-sealed autoclaves operating at 850°C and 2 kbar for 24 hours. The H 2 O concentration of homogenized MIs from the Land’s End granites determined by confocal Raman spectroscopy range between 1.5 and 5.4 wt. %. Several MIs from the Land’s End granites contain a hypersaline fluid with 18.2 to 38.6 wt. % H 2 O. Such mixed fluid and silicate-MIs are typical for magmas that were oversaturated in volatiles. The ratio of silicate glass/saline phase decreases with increasing degree of differentiation of the granite host. The H 2 O content of MIs from the Niederbobritzsch granite, Schönfeld rhyodacite, Teplice rhyolite, Altenberg-Frauenstein microgranite and Schellerhau granite in the eastern Erzgebirge varies between 0.7 and 11.9 wt. %. The MIs from the volcanic rocks have more variable concentrations than the MIs from the granites. The high chemical discrepancies between MIs and whole rock suggest that the quartz phenocrysts in the Schönfeld rhyodacite were injected into a stratified magma chamber during the course of multiple recharge events at the chamber’s base. MIs from granites from the eastern Erzgebirge do not contain hypersaline fluids, however they have F concentrations of up to 11.2 wt. %. The Li, Be and B contents of representative homogenized MIs were determined by SIMS. The light lithophile element ratios of MIs are constant for each magmatic province despite different fractionation degrees of the host rocks. MIs from rocks of the eastern Erzgebirge volcano-plutonic complex are relatively enriched in Li and Be, whereas MIs in granites of the Land’s End pluton have higher B contents. The distinctive ratio of light lithophile elements of the silicate melt is also reflected in the light lithophile element ratio of the magmatic host quartz. Key-words: melt inclusion, Raman spectroscopy, SIMS, granite, Cornwall, Erzgebirge. 1. Introduction Melt inclusions (MIs) are micro samples of magmatic melt entrapped in crystals which can provide unique information of the pre-eruptive dissolved volatile content (H 2 O, B, F, Cl, C, S) of volcanic rocks and the volatile content of granitic mag- ma from distinct stages of their evolution. Quartz crystals in felsic igneous rocks are relative stable and incompressible hosts of MIs, shielding MIs against degassing and preventing other mass flows into or out of the MI system (see Lowen- stern, J.B., 2003). Dissolved volatiles greatly influence the rheological properties of the magma, thus determining the ex- plosive behaviour of volcanic eruptions. The enrichment of B, F, Cl and H 2 O in the apical part of a magma chamber has an acceleration effect on the fractionation of the melt and on the enrichment of metals (e.g. Webster et al., 1997; Aud´ etat et al., 2000; Lehmann et al., 2000; Thomas et al., 2003; Webster et al., 2004; Thomas et al., 2005), which may result in rare and precious metal mineralization. Thus, the chemical character- ization of MIs can be used to address fundamental questions regarding the origin and evolution of the magma and the pro- cesses of magma recharge, crystallization, volatile and metal enrichment, degassing and, ultimately, eruption which take place in shallow felsic magma chambers (e.g., De Vivo & Bodnar, 2003 and references therein). The present study documents the H 2 O contents, and to a lesser extent the concentrations of major, minor elements and light lithophile elements (LLE: Li, Be, and B), in MIs of late-Variscan granites and rhyolites from the Land’s End pluton in Cornwall and the eastern Erzgebirge volcano-plu- tonic complex. These granite complexes are well document- ed in terms of their origin and evolution (e.g., Charoy, 1979; Van Marcke de Lummen, 1986; Powell et al., 1999; Müller et al., 2006 for the Land’s End pluton and Tischendorf, 1989; Breiter, 1997; Förster et al., 1999; Breiter et al., 2001; Müller et al., 2000; ˇ Stemprok et al., 2003; Müller et al., Eur. J. Mineral. 2006, 18, 429–440 DOI: 10.1127/0935-1221/2006/0018-0429 0935-1221/06/0018-0429 $ 5.40 2006 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart