Geochronological constrains on the origins and early geodynamic evolution of the Peloritani Mountains, southern Italy

In situ SHRIMP U-Pb ages have been obtained, for the first time, for detrital zircons from metasedimentary and metaigneous rocks from the Peloritani Mountains (NE Sicily), allowing some firm constraints to be put on the formation age and origins of this still poorly known peri-Mediterranean chain. The greywacke protoliths of the paragneiss forming the most common rock-type in the Peloritani Mountains were deposited at ca. 550 Ma, the age of the youngest detrital zircon population, just before the intrusion of granitoid plutons at ca. 545 Ma. Large portions of flysch-type sequences including deeper equivalents of the ca. 550 Ma greywackes underwent partial melting, producing large volumes of granitoid rocks now exposed as augen-gneisses in north-eastern Sicily, as well as in southern and northern Calabria. Age spectra of detrital and inherited zircons from paragneiss and augen gneiss, respectively, indicate sediment derivation from the erosion of Neoproterozoic to Late Archean sources. The main components are ca. 540-850, 900-1100 and 2400-2700 Ma and minor ones ca. 1.60, 1.80 and 3.20 Ga. These age groups reflect a peri-Gondwanan affinity and are consistent with deposition in a marginal basin located at the northern Gondwana margin, between an old cratonic area and the Avalonian-Cadomian magmatic arc (Nance et al., 2010 and reference therein). The high abundance of Grenvillian zircon, together with the occurrence of ca. 1.56-1.80 Ga grains, makes it quite unlikely that the amphibolite facies basement of NE Sicily was derived from the West African Craton, contrary to what is suggested for similar coeval rocks from Calabria. Although Grenvillian zircons are known from various sectors of northern Gondwana, such as the Saharan craton and the Arabian-Nubian Shield, a stronger affinity with Amazonian-derived terranes, such as NE Bohemia, NW Turkey and the autochthons of NW Iberia, is more suggestive of an Amazonian linkage for that part of NE Sicily at the Precambrian-Cambrian transition. Later, the Peloritani Mountains were involved in break-up processes linked to opening of the Rheic Ocean and, finally, in a short-lived Mid-Ordovician orogenic cycle. Magmatic activity related to this Early Paleozoic evolution is documented, respectively, by Cambro-Ordovician alkali metabasites and Caradocian meta-andesites and felsic porphyroids from the volcanosedimentary sequences of the southern Peloritani Mountains (Trombetta et al., 2004; Cirrincione et al., 2005). The depicted nearly continuous geodynamic evolution suggests a basement-cover relationship between the Latest Neoproterozoic basement rocks of NE Peloritani and the Paleozoic volcano-sedimentary sequences of SE Peloritani. Inherited Mesoproterozoic zircon from the Mid-Ordovician porphyroids (Trombetta et al., 2004) supports both the Amazonian provenance and the basement-cover relationship of the northern and the southern Peloritani Mountains. The results of the present study are in substantial agreement with former models proposed by Acquafredda et al. (1994) and Ferla (2000) and additionally provide the first reliable geochronological information on the real age and early history of the medium-high grade Peloritani basement. Acquafredda, P., Lorenzoni, S., Zanettin Lorenzoni, E. (1994): Terra Nova, 6, 582-594. Cirrincione, R., Fiannacca, P., Lo Giudice, A, Pezzino, A. (2005): Ofioliti, 30, 15-25. Ferla, P. (2000): Mem. Soc. Geol. It., 55, 87-93. Nance, R.D., Gutiérrez-Alonso, G., Keppie, J.D., Linnemann, U., Murphy, J.B., Quesada, C., Strachan, R.A., Woodcock, N.H. (2010): Gondwana Res., 17, 194-222. Trombetta, A., Cirrincione, R., Corfu, F., Mazzoleni, P., Pezzino, A. (2004): J. Geol. Soc. London, 161, 1-13.