The tephra layers in the post-evaporitic Messinian deposits of the Apennines foreland: mineralogical and chemical investigations Teresa TRUA #1 , Vinicio MANZI 1 , Marco ROVERI 1 , Andrea ARTONI 1 1 Dipartimento di Scienze della Terra, Università degli Studi di Parma, Italy # Corresponding author: trua@unipr.it A.59 SS.3 A petrological and geochemical study has been carried out on tephra layers interbedded in the post- evaporitic Messinian deposits of the Apennines foreland. The studied tephra layers belong to three sedimentary sequences (i.e., Maccarone, Campea, and Castel di Mezzo) outcropping in the Adriatic side of the Apennines. According to their stratigraphic position, these layers could represent different outcrops of the same volcanic event, probably occurred 5.5 Ma ago, as suggested by dated layer from the Maccarone section (Odin et al., 1997). The co-genetic character of these tephra layers has been confirmed by this study. Indeed, the studied tephra layers show very similar petrographical and geochemical features. All the studied samples are rich in glass fragments (up to 90 % in volume) with quartz, plagioclase (An38-85), K-feldspar (Or66-95), and biotite as primary magmatic minerals. The glass fragments consist of shards, and micropumice clast up to 400 mm in size. These fragments are fresh, colorless and vesicle-rich. They show a rhyolitic composition (74<SiO2 wt%<79) and a primitive mantle-normalized incompatible element patter typical of that for calc-alkaline volcanic arc magmas. The specific petrological and geochemical features of the Maccarone, Campea, and Castel di Mezzo tephra layers can be used as criteria to identify other corresponding tephra layers outcropping in the Apennines foreland. This should allow to better define the overall spread of tephra deposition and to obtain important information about its possible, still poorly constrained, volcanic source. Indeed, the grain morphology of the glass fragments agrees with a rapid air-fall deposition, occurred immediately after the eruptive event, suggesting a short distance transportation mechanism. Considering that, the Tyrrhenian region seems the most likely source area. But, none of the outcropping calc-alkaline rhyolitic rocks of this region has the same age of these tephra (Serri et al., 2001). Instead, these tephra layers have an age that overlaps a temporal gap observed in the time distribution of the Neogene-Quaternary magmatism of the Tyrrhenian region, suggesting that they represent the only record of an up to now missing volcanic event in the magmatological picture of this region. REFERENCES • Odin G.S, Ricci Lucchi F., Tateo F., Cosca M. and Hunziker J.C. (1997) – Integrated stratigraphy of the Maccarone section, Late Messinian (Marche region, Italy). In: “Miocene stratigraphy: an integrated approach”, Montanari A., Odin G.S., Coccioni R. (eds), Elsevier Science B.V, p. 531-659 • Serri G., Innocenti F., Manetti P. (2001) - Magmatism from Mesozoic to Present: petrogenesis, time-space distribution and geodynamic implications. In: “Anatomy of a mountain: the Apennines and the adjacent Mediterranean Basins”, Vai G.B. and Martini P.I. (eds), Kluwer Academic Publishers (Great Britain), p. 77-104. 64 R.C.M.N.S. Interim Colloquium 2006 “The Messinian salinity crisis revisited-II” 64