Caledonian orogeny

In the transition between Precambrian) and the Palaeozoic (Cambrian) «our» continent, the Baltic Shield, moved away from the continent Laurentia, which includes today’s Greenland and North America, from a spreading zone between the two continents (see timescale here ). The continents were separated by the ancient sea Iapetus. Later, in the transition between Cambrian and Ordovician, the process was reversed by the formation of collision zones where oceanic crust melted both beneath continent and other oceanic crust.

Volcanic island arcs were formed in the collision zone between two oceanic plates c. 450 million years ago, and granite crystallized deep in the crust beneath (fig. 1).

About 420 years ago, between Silurian and Devonian, the two continents collided  and formed the Caledonian mountain range, also called the Caledonides (fig. 2). The relatively young granite and other rocks, as schist metamorphosed of marine sediments, and on Leka also conglomerate and basalt was pushed above the Baltic Shield.

Leka Lauhatten mot øst12_04økt kontrast

Figure 1: The photo is taken of the granittic mountains on Mainland Helgeland, where the most famous is Heilhornet to the right, seen from Leka, and the rocks are called the Bindals-batholith.


Figure 2: A sketch showing how the Baltic Shield and Laurentia collided and formed the Caledonides in the contact-zone, as also the mountain chain between Greenland and Scandinavia is called.

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