Analysis of post-metamorphism brittle deformation in marbles: insights from Montagnola Senese, Northern Apennine

The Tuscan marbles, primarily exposed in the Alpi Apuane Metamorphic Complex and the Montagnola Senese ridge, record a protracted deformation history spanning the rheological spectrum from ductile flow to brittle fracturing. While the syn-metamorphic ductile evolution of these units has been extensively studied, the subsequent brittle deformation—specifically post-metamorphic faulting and fracturing—remains poorly constrained. These fracture networks are not only uplift-related features; they record a polyphase brittle history with direct implications for fluid migration, quarry slope stability, and Neogene–Quaternary stress field reconstruction.

In this work, we characterize brittle structures within marble from the Montagnola Senese, located along the Mid-Tuscan Ridge in the Northern Apennines. This marble has been quarried since Roman times, making rock mass characterization relevant for both scientific and practical purposes. We adopt a multidisciplinary approach, integrating classical field surveys with 3D digital outcrop models obtained by photogrammetry. Data were collected at the outcrop scale and subsequently extrapolated to define the fracture pattern across the entire Montagnola Senese ridge.

The detected fractures and faults cut the marble schistosity, therefore post-dating the last metamorphism event (middle Miocene). Our results reveal at least two brittle deformation phases: (I) a first, left-lateral strike-slip system, followed by (II) extensional structures, which crosscut or reuse the previous ones. Fracture attributes, such as fracture intensity and density, within the non-faulted rock mass were compared to those associated with fault damage zones. These data provide constraints on both quarrying operations and fluid circulation models, whilst contributing to the definition of the tectonic setting of this sector of the Mid-Tuscan Ridge from the middle Miocene to the present day.