When and where did hybridization occur? The case of the Monte Capanne Pluton

The Monte Capanne pluton was emplaced during the Late Miocene in a post-collision extensional regime that generated the Tuscan Magmatic Province as the Adriatic (lower) plate underwent progressive crustal delamination. This dominantly monzogranitic pluton, generated by hybridization between mantle and crustal magmas, consists of mappable facies; end members range from less hybridized with high concentrations of very coarse K-feldspar mega- crysts and abundant mafic microgranular enclaves, to more hybridized with low megacryst and enclave abundances. K-feldspar megacrysts from Monte Capanne and other related units of the province, along with their inclusions and associated late mineral phases, preserve evidence of chemical and 87Sr/86Sr disequilibrium (first rising and then falling) during evolution of the system. The concomitant occurrence of contrasting reaction microtextures in accessory phases in this anatectic-hybrid pluton, particularly involving monazite-(Ce), also suggests transient chemical conditions. The ubiquitous mafic microgranular enclaves, typically with high concentrations of xenocrysts from Monte Capanne magma, provide evidence of a highly dynamic system involving vigorous interaction between mafic and felsic magmas. The data suggest that rapid dehydration melting, driven by intrusions of fractionating mantle-derived magma near the base of the crust, was followed by magma mixing and K-feldspar megacryst growth. Segregation and ascent produced the hybridized products now observed at the emplacement level.