Experimental, geochemical, mineralogical and O-isotope constraints on the late-magmatic history of the Fichtelgebirge granites (Germany)

Mineralogical, experimental, geochemical and stable-isotope data give evidence for an aqueous late-stage fluid which develops increasingly from the less to the more highly evolved granites of the Fichtelgebirge. In less-evolved granites only minor chloritization and sericitization, minor hydration and corrosion of zircons, low leachable fractions of Sr and Zr, the nearly chondritic ratios of Zr/Hf and Y/Ho, and rare-earth-element (REE) patterns lacking the tetrad effect provide evidence of a less-differentiated granitic melt system, poor complexing agents and water, with insignificant late magmatic fluid-rock interaction. In the highly evolved granites, albitization, sericitization and fluoritization, ubiquitous hydration and corrosion of zircons, high leachable fractions of Sr and Zr, Zr/Hf and Y/Ho ratios very different from the chondritic ratios, and REE patterns showing a marked tetrad effect point to the presence of a highly specialized fluid system, rich in water and complexing agents, such as fluorine, leading to a marked magmatic-hydrothermal alteration.