Transformación de andalucita a sillimanita en granitos peralumínicos del batolito de los Montes de Toledo: implicaciones petrogenéticas

Abstract

The Montes de Toledo Batholith comprises several felsic peraluminous granitic plutons characterized by the presence of two Al2SiO5 polymorphous: andalusite and sillimanite (as fibrolitic variety). Textural features indicate an igneous origin for andalusite, variably replaced by muscovite and fibrolite around it. We propose a combination of factors to explain this probable magmatic reaction: the decrease in minor element contents of andalusite (Fe, Mg, Mn, Ti) and the increase of volatiles in the melt (B, P, F, H2O) along its cooling. This chemical variation influences the stability of both polymorphs, crystallizing initially igneous andalusite and, when the Fe content decreases, the sillimanite, in relation with muscovite, in a restricted P-T space close to the granite solidus conditions.