Chapter 6 Folding and Faulting Folding Compression causes

Chapter 6: Folding and Faulting Folding • Compression causes buckling • Appears as folds on the landscape • Layers of sedimentary rock pushed: • upwards form anticlines • downwards form synclines • Folding is associated with the closing of oceans

Chapter 6: Folding and Faulting 1. Caledonian fold movement • Oldest mountains in Ireland • Formed around 400 million years ago • American and Eurasian Plates collided closing the Iapetus Ocean • Collision resulted in the formation of fold mountains • Igneous and metamorphic rocks also formed

Chapter 6: Folding and Faulting 2. Armorican fold movement • Munster Ridge and Valley region • Formed around 250 million years ago • Eurasian and African plates collided • Collision resulted in the formation of fold mountains

Chapter 6: Folding and Faulting 3. Alpine fold movement • Occurred around 60 million years ago • Did not affect Ireland • Eurasian and African plate collided • Alps and the Apennine Mountains of Italy formed

Chapter 6: Folding and Faulting 4. Domes • High central point • Sides that slope • Formed in one of two ways: • rising magma raises rock upwards • result of compression • Subject to weathering and erosion • Exposes oldest rocks at the centre of the dome • e. g. the Weald, Sussex, England; Slieve Bloom Mountains in Laois-Offaly

Chapter 6: Folding and Faulting Sagging • Depression in the centre • Steep edges • Formed due to compression • Depression in the centre • Ridges of older rock are exposed • e. g. Paris Basin

Chapter 6: Folding and Faulting Tilting • Earth movement • Uplifting of land • Uneven slope • Weathering and erosion • e. g. Dartry-Cuilcagh Mountains, Sligo, Leitrim and Fermanagh

Chapter 6: Folding and Faulting Escarpments • Sandstone is more resistant than limestone • Creates steep slopes known as escarpments • Gentler slopes called dip slopes form on the other side of the escarpment where there is less resistant rock

Chapter 6: Folding and Faulting • Occurs when rocks within the Earth’s crust experience stress • Result from movement of the Earth’s tectonic plates • Movement may be vertical or horizontal or both

Chapter 6: Folding and Faulting Types of fault 1. Normal fault 2. Reverse fault 3. Tear fault

Chapter 6: Folding and Faulting 1. Normal faults • Occur at constructive plate boundaries • Rocks are subject to tension • Tension leads to the crust stretching • Rocks within the crust fracture along the fault line • Downward movement of land • Between two or more parallel faults, the block of land moves down under the influence of gravity and fills the space • Rift valley or graben e. g. Scottish Rift Valley • Compression may result in land being forced upwards leads to the formation of a block mountain or horst, e. g. Ox Mountains, Sligo

Chapter 6: Folding and Faulting 2. Reverse fault • Occur at destructive plate boundaries • Rocks are subject to compression • Compression causes rocks to fold upwards • Eventually folds fracture • Land moves upward between parallel faults • e. g. Killarney-Mallow Fault Thrust fault = same motion as a reverse fault, but the dip of the fault plane is less than 45°

Chapter 6: Folding and Faulting 3. Tear fault • Caused by adjacent sections of crust sliding past each other horizontally • Also known as a transform fault • e. g. San Andreas Fault, California, USA