• Edges of continents – convergent plate boundaries
• Plate folds as it is squeezed
• Rock doesn’t fracture during uplift – collision at great depths, high temperatures = more flexible – process over a long period – rocks can adjust slowly
Folded structures Elements of a fold
• Upfold/anticline: an arch • Downfold/syncline: a trough
• Limb: joins upfold/anticline to a downfold/syncline
Types of a fold
• Simple fold: Limbs same steepness and length
• Asymmetrical fold: Limbs different steepness and length
• Overfold: Limbs moving in the same direction, one limb pushing over on top of the other
• Recumbent (overturned) fold: Limbs moving in the same direction and horizontal
• Overthrust fold: Fracture in rock structure – one limb pushed over the other – strata no longer aligned
Caledonian Period
• 400 mya • Eurasian and North American plates
• Mountains in Connacht (Nephin Beg), Ulster (Mourne Mts) and Leinster (Wicklow Mts)
• South-west to north-east trend
• Magma intruded into upfolds – formed igneous (granite) and metamorphic rocks (marble and quartzite)
• Minerals (mica and feldspar) formed as volcanic gases cooled slowly
• Originally stood higher than any that currently exist – worn down by years of weathering and erosion
Folding periods Armorican Period
• 250 mya • Eurasian and African plates
• Mountains of Munster such as the Macgillicuddy's Reeks and Galtees
• East-to-west trend
• Smaller when formed than those of the Caledonian Period – folding further away from the point of collision
• Munster ridge and valley landscape
• Caha Mountains to the Comeragh Mountains
• Upfolded limestone created ridges – weathered and eroded
• Underlying sandstone exposed
• Blackwater, Lee and Bandon flow in a west-to-east direction through valleys covered in limestone rock
Alpine Period
• Most recent – peaked 30 mya • African and Eurasian plates
• No subduction – both were continental plates
• Sediments in the Mediterranean Sea uplifted forming Alps and Apennines
• Himalayas, Rockies and Andes were also formed
• Highest mountain ranges on earth today – haven’t undergone the same levels of denudation as older mountains
