Detrital zircon geochronology constraining the fingerprint of the Tuscan metamorphic unit in the Monticiano–Roccastrada Ridge (southern Tuscany, Italy)

The meta‑sedimentary rocks of the Tuscan metamorphic unit in the Italian Northern Apennines preserve a detrital record of sediment routing, basin evolution, and long‑term interactions between tectonics and surface processes along the western margin of the Adria Plate during the Paleozoic and Mesozoic. These successions were deposited unconformably onto a pre‑Variscan basement and were subsequently involved in Alpine deformation during the Cenozoic, obscuring the original stratigraphic relationships. Nevertheless, the predominance of greenschist‑facies metamorphism, with only localized high‑pressure conditions, allows the preservation of primary sedimentary facies and mineralogical signatures that retain information on sediment sources, transport pathways, and depositional environments.

In the Monticiano–Roccastrada Ridge (southern Tuscany), the stratigraphic succession records middle–late Paleozoic to early Mesozoic deposition across a range of tectono‑sedimentary settings, from deep‑marine basins to continental alluvial systems. This variability reflects spatial and temporal changes in subsidence, sediment supply, and accommodation linked to tectonic activity along the northern Gondwana active margin. However, the age and architecture of the lower part of the succession remain debated, mainly due to limited exposure and discontinuous stratigraphic contacts.

Within the framework of the Italian Geological Survey CARG geological mapping project (Foglio 307, Roccastrada), we integrate detailed field mapping, petrographic analysis, and detrital zircon U–Pb geochronology to reassess stratigraphic correlations and provenance patterns. Results from these meta‑sedimentary units contribute to a refined reconstruction of the paleogeographic and tectonic evolution of the northern Gondwana margin, a key but poorly preserved segment of the Mediterranean geological record.