The Fornovolasco area (Alpi Apuane, Northern Apennines): a review and update on its Palaeozoic succession, middle Permian magmatism, and tectonic setting

Abstract

This study aims at refining the geological setting of the Fornovolasco area in the southern part of the Alpi Apuane (Northern Apennines, Italy). Due to the occurrence of Palaeozoic units of debated origin and age, its structural setting is the key for the comprehension of the evolution of the easternmost sector of the Alpi Apuane. In this context, we combined a 1:5,000 scale field survey with microfloristic and organic matter study, and petrographical and structural analysis. By means of this approach, we obtained the following results: (a) the “Fornovolasco schists” consists of two different lithostratigraphic units: (i) quartz-metasandstone with interbedded levels of graphitic metapelite, characterized by upper Cambrian (Miaolingian-Furongian) acritarch microflora and relatable to the Filladi inferiori Fm; (ii) graphitic metapelite, fine-grained metasandstone and metabreccia, with a well-preservedand diversified middle-upper Permian sporomorphs microflora, making it possible to correlate this unit with the Montignoso Formation. This evidence documents, for the first time, the occurrence of a post-Variscan Palaeozoic unit in the eastern Alpi Apuane.(b) The “Fornovolasco schists” hosts centimetre-thick tourmaline veins and a diffuse network of felsic sheet-like dyke plutonic bodies, supporting widespread magma intrusion associated with hydrothermal activities framed in the post-Variscan magmatism.(c) The studied area consists of three stacked first-order tectonic units: the Tuscan Nappe, Panie Unit, and Apuane Unit. These are characterized by superposed deformational structures of which development was assisted by low-to very-low-grade metamorphism developed during underplating and subsequent exhumation events.