Reaction microtextures of REE–Y–Th–U accessory minerals in the Monte Capanne pluton (Elba Island, Italy): a possible indicator of hybridization processes

Abstract

The study of accessory minerals in granitoid rocks can provide clues to the history of magmatic processes. In particular, the textural–chemical characteristics of accessories could represent effective markers of hybridization processes. The concomitant occurrence of contrasting reaction microtextures of REE–Y–Th–U accessory minerals in the Monte Capanne anatectic–hybrid pluton suggests the occurrence of transient chemical conditions (alumina saturation up and down in the same system) in the early stages of crystallization. Incongruent dissolution of apatite produced microcrystal clusters of huttonitic monazite, while monazite-(Ce) crystals were replaced by allanite-(Ce)±apatite assemblage at the same location. A magma mingling process, involving acidic peraluminous and mafic metaluminous end-members, can provide the expected initial strong differences in alumina saturation that are able to induce such contrasting reactions. The proposed double exchange of accessory minerals between the two magmas strongly suggests a dynamic setting (stirring and straining of crystal-rich melts) in which anatectic and hybridization processes evolved.