The aim of this paper was the U-Pb zircon dating in paragneiss of the Castagna Unit outcropping in Catena Costiera (CC) and Sila Piccola and in augen gneiss of the same Unit outcropping in CC to evaluate the similarities or the differences of the geological evolution of the continental crust portions belonging to the same unit and dislocated along the Alpine Chain in Calabria. The measured ages in the paragneiss from Sila Piccola form clusters at 2700 Ma, 2100 Ma, 1700 Ma, 1031-722 Ma, 637 Ma, 559-515 Ma and 499-421 Ma. These ages are comparable with those measured in augen gneisses of Sila Piccola (Fornelli et al., 2014). The magmatic protoliths of augen gneisses intruded an older metamorphic basement (paragneiss) at about 540 Ma and the whole sector was involved by Ordovician-Silurian tectonic. Both metasedimentary rocks and augen gneisses record the same geological events. In the paragneiss from CC the measured age clusters are 2700 Ma, 2100 Ma and 1025-864 Ma and only one age at 638 Ma. In the two samples of augen gneisses from this area, the whole measured ages form clusters at: 1612 Ma, 975- 758 Ma, 583-512 Ma, 508-495 Ma and one age at 327 Ma. The revealed ages in augen gneisses from CC, are comparable with the ages measured in other augen gneisses both from Calabria and Sicily, except the record of Variscan metamorphism (327 Ma) emerged only in CC area. A different geological history, instead, results by paragneisses from CC considered as host basement of Neoproterozoic-Cambrian acidic magmatism (Fornelli et al., 2014). In these paragneisses are missing the records of: 1) Ediacarian magmatism (540 Ma, intrusion ages of protoliths of augen gneisses); 2) Ordovician-Silurian tectono-thermal event (495-420 Ma); 3) Variscan metamorfism (327 Ma). The missing of these ages in the paragneiss of CC represents a problem. Two hypotheses can be made: 1) the data ages are scarce, more determinations must be performed on other samples; 2) a different geological history was followed by the two sectors of continental crust, in particular, the paragneisses from CC could not represent the basement in which the protoliths of augen gneisses were intruded and, in addition, the augen gneisses outcropping in CC were involved by Variscan metamorphism resetting the zircon age, that for the first time emerges in these rock types. In fact the augen gneisses in Calabria and Sicily display a comparable spectrum of zircon ages comprised between 3242 Ma (Williams et al., 2012) and 421 Ma without Variscan ages.
U-Pb LA-ICP-MS data on zircons from paragneisses and augen gneisses of Castagna unit in Catena costiera and Sila piccola (Calabria)
Fornelli A.;Micheletti F.
2017-01-01
Abstract
The aim of this paper was the U-Pb zircon dating in paragneiss of the Castagna Unit outcropping in Catena Costiera (CC) and Sila Piccola and in augen gneiss of the same Unit outcropping in CC to evaluate the similarities or the differences of the geological evolution of the continental crust portions belonging to the same unit and dislocated along the Alpine Chain in Calabria. The measured ages in the paragneiss from Sila Piccola form clusters at 2700 Ma, 2100 Ma, 1700 Ma, 1031-722 Ma, 637 Ma, 559-515 Ma and 499-421 Ma. These ages are comparable with those measured in augen gneisses of Sila Piccola (Fornelli et al., 2014). The magmatic protoliths of augen gneisses intruded an older metamorphic basement (paragneiss) at about 540 Ma and the whole sector was involved by Ordovician-Silurian tectonic. Both metasedimentary rocks and augen gneisses record the same geological events. In the paragneiss from CC the measured age clusters are 2700 Ma, 2100 Ma and 1025-864 Ma and only one age at 638 Ma. In the two samples of augen gneisses from this area, the whole measured ages form clusters at: 1612 Ma, 975- 758 Ma, 583-512 Ma, 508-495 Ma and one age at 327 Ma. The revealed ages in augen gneisses from CC, are comparable with the ages measured in other augen gneisses both from Calabria and Sicily, except the record of Variscan metamorphism (327 Ma) emerged only in CC area. A different geological history, instead, results by paragneisses from CC considered as host basement of Neoproterozoic-Cambrian acidic magmatism (Fornelli et al., 2014). In these paragneisses are missing the records of: 1) Ediacarian magmatism (540 Ma, intrusion ages of protoliths of augen gneisses); 2) Ordovician-Silurian tectono-thermal event (495-420 Ma); 3) Variscan metamorfism (327 Ma). The missing of these ages in the paragneiss of CC represents a problem. Two hypotheses can be made: 1) the data ages are scarce, more determinations must be performed on other samples; 2) a different geological history was followed by the two sectors of continental crust, in particular, the paragneisses from CC could not represent the basement in which the protoliths of augen gneisses were intruded and, in addition, the augen gneisses outcropping in CC were involved by Variscan metamorphism resetting the zircon age, that for the first time emerges in these rock types. In fact the augen gneisses in Calabria and Sicily display a comparable spectrum of zircon ages comprised between 3242 Ma (Williams et al., 2012) and 421 Ma without Variscan ages.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
