17. THE MOBILITY OF IRON, CALCIUM, MAGNESIUM, AND ALUMINUM DURING K- AND Si- METASOMATISM

A common perception among petrologists is that Al is immobile in most geologic processes, and, therefore, the conversion of gabbro with high Al-content (16-18 wt. % Al2O3) to granitic rocks with lesser Al-content (12-13 wt. % Al2O3) by Kand Si-metasomatism is not possible. The mobility of Ca, Mg, and Fe is not doubted in hydrothermal fluids, but Al is thought not to be mobile. Two different terranes are selected in this presentation where myrmekite-bearing granitic rocks occur and in which the mobility of Ca, Mg, Fe, and Al can be demonstrated. Mg and Ca in these terranes are more mobile than Al and Fe, but Al is much more mobile than what might be expected. These terranes involve the concentration of Fe in magnetite and of Al in kyanite, muscovite, and epidote or in sillimanite and garnet.