Zircon inheritance in an igneous rock suite from the southern Adamello batholith (Italian Alps)

摘要: Zircons from a suite of basic to acidic calcalkaline igneous rocks the southern Adamello batholith (S AB), Southern Alps, N Italy, display complex U−Pb isotopic patterns which are mainly due presence variable amounts isotopically heterogeneous, inherited radiogenic Pb, and minor postmagmatic loss Pb. Inherited Pb is composed 1) ∼ 1100 Ma component located in zircons devoid visible cores 2) 450 associated with conspicuous bubble-rich turbid cores. In concordia representation data points conform lower intercept ages 40 Ma. A linear fit three samples granodiorite defines an intrusion age 39.3 systematics zircon (in particular U content) crystal morphology clearly related. type G1, form relatively late crystallization sequence, consistently show highest contents each population. These zircons, however, not lead. population granodiorite, randomly distributed throughout morphological spectrum. The old components all investigated furnishes proof for involvement crustal material genesis S AB rocks. Samples characterized by ɛNd ɛSr values usually enhanced inheritance. Inheritance varies differentiation reaches maximum intermediate members; these compositions Zr saturation temperatures calculated rock spectrum studied. Textural relations between major phases indicate that magmas leucocratic were saturated at early stage crystallization. On other hand, solubilities textural show, melts Zr. Extension solubility model mineral/melt mixtures tonalitic bulk composition demonstrates residual melt drastically reduced plagioclase amphibole. Survival xenocrystic mafic can best be explained terms dissolution kinetics. Since temperature H2O content Zr-undersaturated favourable rapid dissolution, trace-element rich unstable cores) cannot have been exposed such conditions over extended time periods. Therefore, or more derived sources slow processes as burial metamorphism.