The apuan alps are one of the Most interesting areas in the northern apennines in that they form a tectonic window where the deepest structural layers of the chain can be observed. The apennines are a thrust-and-Fold chain that originated in the tertiary period due to the overlapping from west to East of the ligurian units onto the external tuscan and umbria-marchigiana domains. The apuan metamorphic complex is composed of two overlapping tectonic-metamorphic units: the apuan unit (“autoctono” auct.) And the Massa unit above. Both have a palaeozoic basement which a discordant metasedimentary sequence lies upon triassic –oligocene for the apuan units and middle triassic for the Massa unit. The different varieties of marble, metabreccias and calcschist occur in different strata inside this sequence from which a wide range of materials are quarried commercially known as Apuan marble varieties.
These marble varieties have played a fundamental role in the evolution of the apuan alps that is characterised by two main tectonic-metamorphic events (d1 and D2). Consequently the resulting carbonatic rocks can absorb large quantities of stress and undergo plastic deformation even at low temperatures.
The first event, which occurred between 27 and 20 million years ago, Was the result of a gradual deformation that can be related to the tectonic subduction of the continental crust during which the original tuscan domain Was lowered to middle to deep structural layers (18-30 km) and subjected to regional metamorphism processes of high pressure green schists facies (between 350 and 500 °C and pressure between 0.4 and 0.8 gpa).
The following event, which occurred between 11 and 8 million years ago, can be associated to the rising of the metamorphic units back towards the surface. These phases particularly affected the metasedimentary layers, generating complex deformative structures that in turn influenced all the meso and micro-scale variability in the Apuan marble varieties.
The micro structural variability of the apuan marble varieties May have been known for a long time but has only recently been the subject of in-depth studies due to the fact that it is closely related to the alteration/degradation of the materials and their behaviour in situ.
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