Spoccia Bridge

At Ponte Spoccia, there are thin mafic dikes that have intruded into the schistose rocks belonging to the Cossato-Mergozzo-Brissago (CMB) section.

The CMB line forms the main tectonic boundary between the Ivrea-Verbano Zone and the Lake Series. It consists of a thick band of heavily deformed rocks and, in some cases, recrystallised milonites, with a final high-temperature, low-pressure imprint resulting from the intrusion of mafic magma. The dikes are mostly parallel to the foliation, demonstrating that the CMB Line was already vertical at the time of their intrusion (around 290 million years ago).