Pluton-emplacement-related fracturing in the thermometamorphic marble of Campiglia Marittima (Northern Apennines)

Motivated by the paucity of studies on fracture networks in thermally metamorphosed rocks, in this paper we present and analyse the fracture pattern within the Campiglia Marittima Marble. It is a thermo-metamorphic rock formed during the Neogene emplacement of a granitic pluton in western Tuscany (Italy), in the inner portion of the Northern Apennines thrust belt, affected by post-orogenic back-arc extension. To obtain data from inaccessible outcrops, increase the number of measurements, and capture fracture characteristics at multiple scales, we integrated fracture digitization on 3D Virtual Outcrop Models with the traditional field mapping. Our results show that the fractures on the cap rock around the top of the pluton are clustered into radial and concentric patterns. Furthermore, in the whole metamorphic aureole, fractures cut metamorphic features, such as folds or schistosity, confirming that brittle deformation postdates the metamorphic event. Away from the pluton emergence, the orientation of fractures aligns with regional-scale extensional trends. Therefore, we interpret the fracture distribution as due to the pluton rise, which acted as a “localised” stress source during its ascent, deforming the already cooled marble under brittle conditions.