Rare elements enrichment in crustal peraluminous magmas: insights from partial melting experiments

Experiments were conducted to explore the behavior of Li, Rb, Nb, Sn, Cs, Ta, W during crustal melting and test anatectic origin rare metal-bearing peraluminous granites such as metal (RMGs). The experiments performed under fluid-absent conditions at 800 850 °C, 400 MPa moderately reducing fO2 (ΔFMQ = − 0.5 0.8). Starting materials cores several millimetres drilled from two natural rocks, a biotite-rich paragneiss (Pg) muscovite-rich orthogneiss (Og) enriched in Be, W. Both protoliths produced small melt fractions 8 20% vol. Melt distributions either homogeneously distributed grain boundaries Pg or preferentially associated with muscovite reaction zones Og. In is mainly fluid present, driven by interstitial water boundaries. At biotite dehydration-melting produces peritectic orthopyroxene, hercynitic spinel, ilmenite alkali feldspar addition melt. Og, generates plus biotite, ilmenite, Al silicates feldspar. Experimental glasses are nearly homogeneous, silica rich, leucogranitic their major element compositions differ only little between protoliths. contrast, trace concentrations vary consequence chemical textural heterogeneities our starting materials. Compared source Og depleted Cs Ta. Mass-balance calculations indicate that dehydration-melting, Rb partition into melt; whereas Ta incorporated phases. Li also toward dehydration-melting. partitioning elements function coefficients melt, residual similar but fail reproduce RMG compositions. Alternatives mica fluid-present emphasize difficulties an RMGs purely processes. Crystallization differentiation might have be combined explain distinctive geochemical features RMGs.