Some of the Alpine Units of the nappe pile of Calabria (southern Italy) include blocks of Variscan continental crust. Among these, the Castagna, Sila and Aspromonte Units containing felsic augen gneisses are here considered. These augen gneisses are abundant in the Castagna and Aspromonte Units, whereas are scarce in the lower crust segment of the Sila Unit. Spot U-Pb zircon-dating revealed Latest Precambrian-Early Cambrian emplacement of the magmatic protoliths of the augen gneisses from the three units with Neoproteozoic, Palaeoproterozoic and Archean inheritances. Geochemistry and Sr, Nd isotope signatures indicate the protoliths formed in orogenic setting through mixing of crust-mantle melts. The high-K calc-alkaline to shoshonitic nature of protoliths points to a transition between compressive and extensional tectonic setting or even to a collapsed intracontinental orogen formed by amalgamated Cadomian terranes and Gondwana craton. The coeval emplacement of similar melts in the three different units suggests they were portions of the same Pan-African-Cadomian block in Precambrian times. Sr and Nd isotope signatures evidence that these magmas cannot be derived from the partial melting of the now exposed restitic metapelites of the lower crust segment of the Sila Unit. More likely the basement containing the augen gneisses was eradicated from the source of the crustal melts during the Variscan orogeny and records recycled terranes derived from West African Craton.
The Neoproterozoic-Early Cambrian felsic magmatism in Calabria (Italy):inferences as to the origin and geodynamic setting
FORNELLI, Annamaria;MICHELETTI, FRANCESCA;PICCARRETA G.
2007-01-01
Abstract
Some of the Alpine Units of the nappe pile of Calabria (southern Italy) include blocks of Variscan continental crust. Among these, the Castagna, Sila and Aspromonte Units containing felsic augen gneisses are here considered. These augen gneisses are abundant in the Castagna and Aspromonte Units, whereas are scarce in the lower crust segment of the Sila Unit. Spot U-Pb zircon-dating revealed Latest Precambrian-Early Cambrian emplacement of the magmatic protoliths of the augen gneisses from the three units with Neoproteozoic, Palaeoproterozoic and Archean inheritances. Geochemistry and Sr, Nd isotope signatures indicate the protoliths formed in orogenic setting through mixing of crust-mantle melts. The high-K calc-alkaline to shoshonitic nature of protoliths points to a transition between compressive and extensional tectonic setting or even to a collapsed intracontinental orogen formed by amalgamated Cadomian terranes and Gondwana craton. The coeval emplacement of similar melts in the three different units suggests they were portions of the same Pan-African-Cadomian block in Precambrian times. Sr and Nd isotope signatures evidence that these magmas cannot be derived from the partial melting of the now exposed restitic metapelites of the lower crust segment of the Sila Unit. More likely the basement containing the augen gneisses was eradicated from the source of the crustal melts during the Variscan orogeny and records recycled terranes derived from West African Craton.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
