Nivia Bridge

At Ponte Nivia, the banded amphibolites of the Strona-Ceneri boundary zone can be seen. This unit consists mainly of rocks of amphibolite facies derived from Precambrian (555 million years ago) basaltic pyroclastic rocks.

Around 470 million years ago, acidic magmatic residues, originating from granitic intrusions, intruded into the permeable pyroclastic rocks, particularly those with a coarser grain size. The subsequent amphibolite-facies metamorphism associated with a Carboniferous orogeny (the Hercynian or Variscan orogeny) did not obliterate the structures formed during these events (megacrystals of feldspar in the coarser-grained parts). The main mineralogical composition of these rocks consists of hornblende and plagioclase; in the ‘feldspathic’ layers, potassium feldspar, quartz and biotite are also present in varying quantities.

Walking downstream along the Nivia stream from the ancient arched bridge, you can observe every stage ofthe ‘feldspathisation’of the amphibolites.