GL5 Geological Evolution of Britain OROGENIES 1. What is an OROGENY ? 2. When would an orogeny occur ? 3. What kind of features do OROGENIES form ? 4. Name one OROGENY that affected the UK. Credit: U.S. Geological Survey

Variscan/Hercynian/Amorican Alpine OROGENIES that affected the UK : Caledonian Variscan/Hercynian/Amorican Alpine *** Remember - these mountain building phases can have an effect over very large areas so the evidence for them may not only be found in the UK but may be found on other continents too.

THE CALEDONIAN OROGENY Effects seen in Scotland, the Southern Uplands, the Lake District and Snowdonia Effects seen in Pre-Cambrian, Ordovician and Silurian rocks Occurred between 600 & 400Ma Created the Caledonian fold belt A result of the Laurentian continent (Greenland and Canada) colliding with Gondwanaland (Scandanavia and Baltic continent) Involved the closure of the Iapetus Ocean – between Scotland and England Resulted in volcanics in Snowdonia (Mount Snowdon) and the Lake District (ScaFell Pike, Old Man of Coniston etc.) Main trend of fold axes = NE-SW Associated with the Moine Thrust, the Highland Boundary Fault, the Great Glen Fault and the Southern Uplands Fault – with NE-SW trends Associated with major intrusions in Scotland eg. the Carrock Fell gabbro

THE VARISCAN OROGENY Also known as the AMORICAN OROGENY Also known as the HERCYNIAN OROGENY Effects seen in Devon and Cornwall, South Wales, and northern England Effects seen in Devonian & Carboniferous rocks Occurred about 290Ma Created the Variscan mountain belt A result of southern Europe colliding with the Caledonian continent to from Pangaea - supercontinent Involved the closure of the Rheic Ocean – between South Wales and Devon and Cornwall Resulted in intrusions and volcanics in Devon and Cornwall – including the Cornubian batholith - granites Resulted in intense folding such as that at Hartland Quay, Devon and Millook, Cornwall along with folding of the South Wales coal fields Main trend of fold axes = E – W Associated with the formation of the Lizard Thrust, the Pennine Block faults and renewed subsidence in the Scottish Rift valley Associated with the intrusion of the Whin Sill

THE ALPINE OROGENY Effects seen mainly in South East of England Effects seen in Permian, Triassic, Jurassic, Cretaceous and Tertiary rocks. Occurred about 25 - 30Ma Created the Alpine mountain belt – the Alps Created the Wealden Anticline Created the Lulworth Crumple, Dorset Main trend of fold axes = E-W Re-activated many pre-existing fault lines Was centred in Southern Europe and the UK only on the edge of the mountains formed A result of northward movement of Africa colliding with Europe The north Atlantic was opening up at the same time – producing the flood basalts seen in Northern Ireland (Giants Causeway) and north-east Scotland (Staffa and Fingal’s Cave) and dyke swarms across northern England and southern Scotland.