Vocca Island 2

The rocks at this geosite are gabbros, which crystallised from basaltic magmas at a depth of around 25 km within the continental crust: these are the deepest levels of the gabbro complex, known as the Basic Complex, and are 8 km thick (from here to Varallo); it formed through continuous magma intrusions into the deep crust between 290 and 282 million years ago.

The light and dark grey bands correspond to different abundances of the minerals plagioclase (light) and pyroxene (dark). The magma that formed these rocks reached temperatures of over 1200°C: the intense heat generated by this gigantic intrusion was the driving force behind the magmatic system of the Sesia supervolcano.