Monte Rosa Massif

The Monte Rosa massif is a folded mountain range with overlying strata, consisting mainly of ancient gneisses and mica schists of European origin (Pennidic Domain) dating from the Precambrian era (over 550 million years ago), which have been profoundly altered by massive metamorphic processes (both pre-Alpine and Alpine) and affected by complex tectonic displacements resulting from the collision between the European and African plates. This process (which began around 65 million years ago, at the end of the Cretaceous period) led to crustal shortening, the uplift of rock layers, their folding and sliding over one another, and thus to the formation of the Alpine Range.

The geological formation to which most of the rocks making up this mountain range belong is the Monte Rosa Formation.

It consists mainly of highly metamorphosed, aluminium-rich paragneisses containing biotite, garnet, quartz-K-feldspar-sillimanite-plagioclase-muscovite, often banded, into which granites and aplitic dikes of Late Hercynian age (300 million years) have intruded, subsequently transformed by Alpine metamorphism. Among the latter, the most common lithotype is a two-mica granitic orthogneiss, easily recognisable by the presence of large orthoclase crystals which give it a glandular structure (hence the name ‘ghiandone’). Associated with this lithotype are fine-grained granitic orthogneisses and, finally, aplitic orthogneisses, often with an eye-like structure, which form an extensive vein-like complex, recognisable as a series of large, light-coloured bands within the paragneisses. The Alpine orogeny has often transformed these rocks into mica schists and micaceous-granate-bearing paragneisses, in which white mica and reddish garnet abound, even in large crystals. Intercalated amongst the mica schists and paragneisses are numerous ophiolites (basic rocks of oceanic origin), generally consisting of amphibolites and eclogites, sometimes associated with marbles (Fürgg Zone).

Above the Monte Rosa Formation lies the Piedmontese Zone of Calcareous Shales with Greenstones. This corresponds to an ancient oceanic basin consisting of both plutonites and submarine basic volcanic rocks (collectively referred to as ophiolites), as well as marine calcareous and siliceous sediments (which are now found in the form of calcareous schists, marbles and quartzites). The Piedmontic Belt is divided into two structural elements: a lower one, where ophiolites of medium-to-high metamorphic grade clearly predominate (due to reaching greater depths along the subduction zone), and an upper one, where rocks of sedimentary origin alternate with ophiolites of low-to-medium metamorphic grade. In the lower unit, one thus finds serpentinites (sometimes highly laminated), amphibolites and eclogites – all of a massive, dark-coloured appearance – as well as metagabbros and flasergabbros; in some areas, manganese quartzites and veins of rodingitic gabbros are found, enriched in garnet and epidote due to metasomatic reactions between the serpentines and the host rocks.

In the upper unit, we find silvery-brown calcareous schists, phyllites, impure marbles and quartzites associated with prasinites of a characteristic pale green colour speckled with white, dark and compact serpentinites, and, to a lesser extent, metamorphic gabbros and amphibolites. The tectonic contact between the Monte Rosa Nappe and the Piedmont Zone is often characterised by the presence of highly schistose and foliated serpentinites, as well as layers of light-green talc schist and chlorite schist that are crumbly and greasy to the touch; this type of structure bears witness to the intense mechanical deformation processes that took place during the stacking of the strata.

During the final stages of Alpine orogenesis (in the Lower Oligocene, around 32 million years ago), intense tectonic movements caused hot, silica-rich hydrothermal fluids to rise along fractures and schistosity planes within the rocks of the Monte Rosa Massif. As they cooled towards the surface, the fluids released their mineral content, forming lodes and veins, composed mainly of quartz gangue with disseminated gold and sulphides such as pyrite, which extend from the Anzasca Valley through the Valsesia to the Val d’Ayas. These veins constitute Italy’s most important gold-mining district.

The Monte Rosa glaciers included within the Geopark’s boundaries are Bors, Piode, Locce Sud, Sesia and Vigne. Snowfields such as Parrot, Puio and Otro can also be seen. The glaciers are the defining features of the natural landscape of the upper Valsesia. Their location amongst the famous peaks of Monte Rosa has meant that they have been observed by mountaineers and naturalists since the 19th century.