Granite from Argentera
We recycle !! This site is made up of rocks from old materials.
A link in the history of the Alps….
Long before the Alps, a huge mountain chain called the Variscan (or Hercynian) chain was formed between - 420 and - 290 million years ago during the primary era. With more than 5 km long and several hundred km wide, geologists often compare it to the Himalayan range.
It was born from the collision of two great continents which, when united, formed Pangea. This immense single continent covered a third of the surface of the globe. The other two thirds were occupied by the Panthalassa and Paléotéthys oceans.
Between 360 and 330 million years ago (Lower Carboniferous), the collision results in the formation of a continental crust, very thick, which can measure up to 70 km in depth. Rocks, buried at great depth and exposed to high temperatures, melt partially or totally while cooling slowly. They recrystallize thus forming new rocks: migmatites (from migma: mixture) and granites.
Between 320 and 300 million years ago (Upper Carboniferous), when the collision came to an end, erosion removed a large part of the reliefs formed. The crust is thinned and a new generation of granites takes place, marking the end of Varisque history.
Those of Argentera, dated 295 million years ago, therefore belong to these so-called late-orogenic granites. They originated by melting the crust at a depth of 30 km. The magma thus formed migrates slowly upwards. In its upward movement, it causes the melting of older rocks, such as migmatites.
Its slow cooling allows it to crystallize, forming crystals of quartz, feldspars and mica, large enough to be visible to the naked eye. This composition and coarse-grained texture are characteristic of a granite.
Most of the rocks of Argentera – Mercantour are of deep origin or have been transformed at depth. Only a part of them, which reached the surface at the end of the orogeny, has undergone intense erosion. The other rocks, remained in place in the continental crust, awaited their next recycling in the following adventure: that of the history of the Alps.
Find out more about the "recycling" of rocks
The surface of the Earth is constantly changing. Indeed, the plates that compose it move with respect to each other, forming and deforming the earth's crust. This phenomenon is called plate tectonics.
In general, here are the main steps involved in this recycling mechanism:
- Continents are tearing apart and giving way to growing oceans. In other parts of the globe, the plates are approaching and clashing. The ocean floor plunges to be recycled in depth, it is subduction.
- The continents, once separated by an ocean, collide to form one. As a weld, a mountain chain is formed. By very active erosion, materials are torn from the reliefs, then when the landscape flattens out, the sands, clays and gravel spread out in immense alluvial plains. A new cycle can then begin ...
… In connection with 22 other geosites: Daluis, Verdaches
Nothing is lost, everything is transformed ! The erosion of the Variscan chain has generated a quantity of sediment accumulated in alluvial or deltaic plains, lakes and down to the bottom of the oceans.
At the end of the Carboniferous (-305-300 million years ago), sediments accumulate in marshy alluvial plains, as evidenced by the rocks (sandstone, pelites, argillites) of the Verdaches clue.
Then, in the Permian (around -270 million years ago), the sediments accumulated in large collapse ditches announce the transition to the next stage of the Geological Adventure (see the site of the Gorges de Daluis).
What we can decipher from the current landscape
Granites are very hard crystalline rocks. They are clearly distinguished from other types of softer or friable rocks present in the massif. They constitute the highest peaks of Argentera-Mercantour.
A little anecdote?
What is the difference between granite or granite?
Granite is the name of a magmatic rock, made up of three main types of minerals: quartz, feldspars and mica. This siliceous rock is very hard, typical of the continental crust.
Granite is the name given by quarrymen, sculptors and poets (because of a prettier sound!), to any hard and grainy rock, whatever its composition and its origin. Granite comes from the Italian granito: grainy.