Relative dating of geological features

Initially, geology involved the examination and survey of surface rock exposures to prepare geological maps.

More recently, understanding of the evolution of Europe's continental crustal structure has been greatly enhanced by the interpretation of new types of geophysical and geochemical data.

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The present continent of Europe stretches from its submarine continental margin in the west to the Ural mountains in the east, and from the ancient and relatively tectonically stable rocks of the Fennoscandia Shield in the north, to the young, more tectonically and volcanically active zone, of the central and eastern Mediterranean in the south.The evolution of the continent took place as a result of lithospheric plate interactions, which are now relatively well understood.Similarly, throughout the Alps of southern Europe, pre-Alpine basement rocks, including pre-Variscan basement, late-Variscan granitoids and post-Variscan volcaniclastic rocks, occur in many places.Fig 1 The small outcrop of Laurentian, the Lewisian Gneiss Complex of NW Scotland, has remained tectonically stable since Proterozoic times.Also, metamorphic overprinting of some older basement areas has occurred during later orogenic cycles.

This is particularly the case with the Variscan fold belt, which in places seems to contain some Caledonian, as well as the Late Palaeozoic (Devonian-early Carboniferous) orogenic belts.

Orogenesis, involving crustal thickening, deformation and metamorphism, is often followed by extensional collapse with widespread intrusion of highly evolved peraluminous granites.

Plume activity is generally associated with continental break up, and there is considerable evidence of this following the splitting of the Earth's most recent supercontinent - Pangaea, beginning during the Permo-Triassic times.

Whereas, the collision of the Armorican micro-continent, with both the East European Craton and Avalonia, followed the later closure of the Rheic and Theic Oceans (Galiza-Central Massif Ocean, e.g., Matte 1991, Rey et al. The southerly European Alpine orogenic belt is mostly of Caenozoic age.

In Europe, the precise locations of separate terranes, fault-bounded blocks of continental crust, usually smaller than microcontinents, related to Avalonia or Armorica are poorly exposed and concealed beneath younger rocks.

Also, in places, the reworking of older rocks in later orogenies has resulted in collages of relatively small shear-zone-bounded terranes (such as the Precambrian Mona complex of North Wales, and similar complexes in the Bohemian Massif).