Andalusite-sillimanite transformation in peraluminous granites of the Montes de Toledo Batholith: petrogeneticalimplications

摘要

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