Isotopic evidence from the Ivrea Zone for a hybrid lower crust formed by magmatic underplating

The large mafic complex overlying mantle peridotites in the Ivrea Zone of northern ltaly originated by underplating of mantle-derived magma onto the base of continental crust, and may be a unique outcrop of typical mafic lower crust, sampled elsewhere only by mafic xenoliths. Neodyrnium and strontium isotope data show that the magmas assimilated large and roughly uniform proportions of crustal material. The resulting hybrid magmas have the same isotopic signature as, and may represent the lower-crustal 'roots' of, upper-crustal Hercynian granitoid intrusions.