Geometry and kinematics of the Montelanico-Carpineto Backthrust (Lepini Mts., Latium) in the hangingwall of the early Messinian thrust front of the central Apennines: implications for the Apennine chain building

Maurizio Parotto(*) & Marco Tallini(**)
(*) Dipartimento di Scienze Geologiche, Università di Roma Tre, Largo S. Leonardo Murialdo, 1 - 00146 Roma (Italy). (**) Dipartimento di Ingegneria Civile, Edile-Architettura e Ambientale - Centro di Formazione in Ingegneria Sismica, Università dell'Aquila, Via Giovanni Gronchi, 18 - 67100 L'Aquila (Italy). ph.: +39(0)862434553; fax: +39(0)862434548; E-mail: marco.tallini@univaq.it

The paper updates knowledge on the Montelanico-Carpineto Backthrust, which is confined in the Lepini Mts. thrust sheet, at the hangingwall of the Neogene Latina Valley Thrust Front. The local stratigraphic setting consists of a pre-orogenic succession of Mesozoic carbonates from the Latium-Abruzzi platform Auct. The carbonates are paraconformably overlain by Miocene ramp limestones, which evolve upwards into planktonic marls. The Sub-Ligurian unit thrusted over this dominantly carbonate succession. In the Latina Valley, siliciclastic turbidites (Frosinone Formation Auct.), which evolved from the above-mentioned Miocene units, constitute the upper Tortonian foredeep deposits, now preserved in the footwall of the Lepini Mts. thrust sheet. In the Segni-Montelanico area, conglomerates, unconformably overlying the carbonate bedrock and coeval with the Frosinone Formation, are interpreted as late Tortonian thrust-top deposits (Gavignano and Gorga unit). The Lepini Mts. ridge has two series of distinctive tectonic features: the first is related to the Neogene shortening events due to the Apennine chain building; the other results from Plio-Quaternary extensional events associated with the collapse of the Tyrrhenian margin. The Montelanico-Carpineto Backthrust, as evidenced by the structural survey, is a compressive fault plane dipping 45°-50° towards NE with a SW-verging dip-slip kinematics. The fault has an offset of about 700 m, ramp geometries and a cut-off of about 20°. The Montelanico-Carpineto Backthrust and the Latina Valley Thrust Front define a pop-up structure. The presumable age of the Montelanico-Carpineto Backthrust is the early Messinian, because the late Tortonian Gavignano and Gorga unit is involved in its brittle shear zone. This implies that the formation of the Montelanico-Carpineto Backthrust and of the related pop-up structure is coeval with the early Messinian thrusting of the Lepini Mts. thrust sheet upon the geodynamic propagation of the central Apennine chain-foredeep-foreland system.

Fold-and-thrust belt, backthrust, early Messinian, central Apennines.