Interaction between mafic and salic magmas in granitoid plutons as inferred from geochemical and Sr-Nd isotopic study of enclaves and host granitoids from Cima d'Asta, southern Alps, Italy

Major, trace element and Sr-Nd isotopic compositions are discussed for a series of granitoid rocks and hosted mafic enclaves from the Late Hercynian Cima d'Asta pluton, Italy. Mafic enclaves are found in tonalites, granodiorites and granites. The enclaves have variable compositions but most of them display higher K, Rb, HREE, Y, Zr and lower Ca, Mg, Ni, Cr and Sr than the intrusive rocks with the same silica content. Geochemical and textural evidence rules out that the mafic enclaves represent cumulates or restitic material left unmelted during granitoid formation. Field and textural evidence strongly favours the hypothesis that the enclaves represent blobs of mafic liquids emplaced in cooler, partially crystallized intermediate to salic magmas. Geochemical and isotopic data, however, exclude that the mafic magmas preserved their pristine compositions and suggest strong chemical interaction with the host granitoids. A model of equilibration is presented for the enclaves. -from Authors