Crustal Contributions to Late Hercynian Peraluminous Magmatism in the Southern Calabria-Peloritani Orogen, Southern Italy: Petrogenetic Inferences and the Gondwana Connection

Sensitive high-resolution ion microprobe (SHRIMP) analyses of zircon from granites of the medium-high grade Aspromonte-Peloritani Unit, Calabria-Peloritani Orogen (CPO), southern Italy, show that one of the minor trondhjemites (313·7 ± 3·5 Ma) represents the earliest identified occurrence of Late Hercynian peraluminous igneous rocks in the CPO, predating the emplacement of the more common peraluminous leucogranodiorites by about 14 Myr. Some of the trondhjemite zircon grains contain small cores with ages of about 2·45 Ga, 625 Ma and 490 Ma, consistent with the presence of a sediment component in the magma. A newly dated leucogranodiorite (300·2 ± 3·8 Ma) is rich in inherited zircon. Cores with ages of about 2·36, 870 Ma, 630 Ma, 545 Ma and 460 Ma are overgrown by two generations of Hercynian igneous zircon, the first with moderate to high Th/U (up to 1· 67), and the second with low Th/U (< 0·1). The overgrowths probably crystallized from magmas of two compositions, the first metaluminous and the second peraluminous. This could indicate either magma mixing or, more probably, crystallization in a single, evolving magma. In either case, the leucogranodiorite magma is considered to have been the product of anatexis of a metasedimentary source. Differences in the inherited zircon age spectra, and the relatively small amount of inheritance in the trondhjemite, indicate that the trondhjemite and leucogranodiorite are unlikely to be genetically related. The ages of the inherited zircons are consistent with the sedimentary component in both magmas being derived from North Africa, with a possible contribution from Pan-African granitoids similar to those exposed in southern Calabria.