Formation of the Mount Capanne pluton and its thermal metamorphic ring

Six to seven million years ago, a massive body of magma, more technically known as a 'monzogranite batholith' (from the Greek bathos, meaning deep, and lithos, meaning stone), rose up through the Earth's crust and solidified within older sedimentary and ophiolitic units. This is created the Mount Capanne pluton mass, still considered the largest formation of its kind in central Italy and one of the largest in the western Mediterranean, measuring approximately 9 kilometres in diameter.

The phenomenon was massive because the extremely viscous igneous material of acidic composition, produced through fusion of crustal or subcrustal materials, lifted up a huge cap rock into which it progressively intruded and consolidated, injecting veins of molten magma into the overlying levels, disrupting them and altering them from a physical and chemical perspective due to the high temperatures and pressures at work. As plutons form, however, much of the ascending magma remains buried at depths varying from hundreds of metres to several kilometres, cooling and crystallising slowly and only reaching the light of day after long erosive and tectonic processes.

This is a brief summary of the formation of the granodioritic complex more commonly known as the granite massive of Mount Capanne, a rock formation we have already come to know during our walk. As previously mentioned, while the consolidating masses cooled, large quantities of heat were released which, together with the high pressures due to intrusion by new volumes of magma, significantly altered the encasing rocks, creating new lithologies or, in other words, rocks with different physical and chemical characteristics. Around the base of Mount Capanne, what is known as the thermal metamorphic ring is visible where pre-existing serpentine rocks transformed into olivenites, gabbros and basalts into amphibiolites and radiolarites into quartzites.

In the section we are now crossing, we can see limestone, marly limestone and clay layers which have sculpturally and strikingly transformed into marble with varying contents of quartz, diopside and wollastonite, Cipollino, biotite schist and garnetite.

(Antonello Marchese, translation from Italian)