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

Diego Pieruccioni ¹, Amalia Spina ², Andrea Brogi ^3,4, Enrico Capezzuoli ⁵, Martina Zucchi ³, Simone Vezzoni ⁴, Domenico Liotta ^3,4, Andrea Sorci ² & Giancarlo Molli ^6
1Geological Survey of Italy, Institute for Environmental Protection and Research (ISPRA), Via Vitaliano Brancati 60, 00144 Roma, Italy, ²Department of Physics and Geology, University of Perugia, Via Pascoli, 06123 Perugia, Italy, ³Department of Earth and Geoenvironmental Sciences, University of Bari, Via Orabona 4, 70125 Bari, Italy, ⁴Institute of Geosciences and Earth Resources, Consiglio Nazionale delle Ricerche, Via Moruzzi 1, 56124 Pisa, Italy, ⁵Department of Earth Sciences, University of Florence, Via La Pira 4, 50121 Florence, Italy, ⁶Department of Earth Sciences, University of Pisa, Via S. Maria 53, 56126 Pisa, Italy

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, characterised 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-preserved and 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 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 characterised by superposed deformational structures of which development was assisted by low- to very-low-grade metamorphism developed during underplating and subsequent exhumation events.