Geochemical behavior of boron at the magmatic-hydrothermal transition: insights from d11B of tourmaline in peraluminous granites (Elba Island, Italy)

Boron isotopic composition was measured in tourmaline from Elba Island (Italy) magmatic-hydrothermal systems in which the mineral formed through progressive stages of evolution: magmatic (euhedral crystals, spots and orbicules), pegmatitic (graphic intergrowths and miarolitic crystals) and hydrothermal (breccias/veins in intrusives and country rocks). The ?11B are found to be nearly uniform within magmatic progressive tourmaline growth stages (-9.9 to -7.6 ?). Significative differences in ?11B are observed only in tourmaline crystallised in late hydrothermal overgrowths, veins and breccias. Mixing with external, late, hydrothermal fluids is discussed in terms of chemical variations and boron isotopic characters of late tourma-lines crystallized in different geologic settings (plutonic vs. subvolcanic).