Caledonian Mountain range

Some facts

Die kaledonische Gebirgskette ist das älteste Gebirge Europas. Sie wurde zwischen ca. -443 bis ca. -417 Millionen Jahren aufgefaltet und ist ca. 7500 km lang. Heute sind ihre Gipfel weitgehend wegerodiert, so dass Gesteine zutage treten, die einst 20 km unter der Erdoberfläche lagen. Was nicht heißt, dass die Berge 20 km hoch waren, das gibts auf der Erde nicht (siehe unten). Zum Vergleich: Die Alpen wurden zwischen -105 bis -25 Millionen Jahren aufgefaltet (Labhart, «Geologie der Schweiz», Hallwag 1987).

Page numbers refer to Gillen, «Geology and landscapes of Scotland» Terrapublishing, Harpenden 2003

Orogeny

• 7500 km long, extents from the arctic through eastern Greenland and western Norway to scotland and on to the Appalachians.
• The mountain belt grew when the Iapetus Ocean closed and Laurentia and Avalonia collided 420 million years ago (p. 68).
• Several different crustal segments were involved in the collision between the continental blocks of Laurentia, Baltica and Avalonia. (71)
• In the Devonian age (418 .. 362 million years ago, p.110), Scotland lay about 29° south of the Equator.
• A thickness of 20 .. 25 km of material was removed off the mountains. p.110
• The crust beneath young mountain belts forms very thick root zones, down to 150 km. As material is stripped off at the surface, these buoyant mountain roots rise up to maintain the elevation of the chain. (71)
• The latitude of 20° south is the zone where desert conditions exist, and the continental deposits in such an environment are frequently stained red with haematite. (Old Red Sandstone, 110)
• The final stages in the closing of the Iapetus Ocean were accompanied by widespread igneous activity, when many granite bodies intruded the base of the thickened continental crust in the collision zone. (85)
• Melting of the deep thick crust led to formation of granites, which forced their way up into higher levels.
• Mountain top plateau date from the Tertiary period (p. 87) when extensive planation of the land surface took place.

Ice age

• Greatest extend of Scottish ice sheet was 22000 .. 18000 years ago, when almost the entire land surface was under a 2 km thick sheet.
• It is likely that all the mountain tops were covered by ice.
• The maximum thickness of the mainland ice dome was centred on Rannoch Moor, from where the ice spread out radially, creating a pattern of deep narrow lochs and valleys.

Plants, surface

• Plant life during the Devonian period (418 ..362 million years ago) was very sparse on land, being restricted initially to lichens, ferns, reeds and mosses. With no tree or grass cover, the bare stony mountainous terrain was subject to rapid erosion. p.110
• 325 million years ago, in the Carboniferous age, coal formed in dense forests on swampy ground at sea level when Central Scotland was in equatorial latitudes.
• Before the Carboniferous, land plants were not abundant enough to produce the peaty soils that are required to make coal (208).
• By the start of the Carboniferous, the Caledonian Mountains had been worn down by the forces of erosion. Central Scotland was flooded by shallow tropical seas where corals flourished, and limestone formed as a result. (120)

Ben Nevis

• Is part of a granite and lava complex. (77)
• The complex consists of a granite body 7 km wide, within which sits a 600 m thick plug of andesite lava 2 km wide (80).
• Lava is erupted by surface volcanoes, whereas granite forms a depth. Juxtaposition of lava and granite in this way is rather unusual and thus gives hints about the formation of the complex.

Glencoe

• Dalradian schists overlain by younger (Devonian) lavas of Lorne and intruded by the igneous complex of Glencoe.
• The U-shaped valley is made of Dalradian phyllites and schists and was excavated by glacial erosion during the last ice age.
• The Three Sisters (Aonach Dubh, Gearr Aonach, Beinn Fhada) are made of rhyolite lava.
• Many of the rhyolites show fine flow banding that formed as the material was moving over the surface, rumpling and puckering on being pushed from behind.
• Rhyolite is an acidic igeous rock. Such lavas tend to be erupted from highly explosive volcanic vents, in which fast-flowing and highly destructive clouds of extremely hot ash and molten lave droplets are produced.

Last update Donnerstag, 21. August 2008 GVa