Mountain Building

1. Mountain Building Earth Science Ch. 11

2. 11.1 Forces in Earth’s Crust • Deformation: permanent change in the size or shape of rock • Occur along plate margins and in the Earth’s crust. • Stress: force applied to a rock • Strain: change in the shape of rock • Folding: bending due to gradual stress on rock • Fracturing: breaking of rock.

3. Brittle Deformation • At the surface, temperatures and pressures are low • Rocks behave like brittle solids and fracture once their strength is exceeded. • Ductile Deformation • At depth, temperatures and pressures are high and rocks become ductile. • Deep inside the Earth, a solid state flow occurs • Material under high temperatures and pressures are more likely to change shape and do not fracture.

4. Rock type can also affect deformation • Igneous rock is more likely to fracture than sedimentary or metamorphic rock. • Sedimentary and metamorphic are more likely to fold before they will fracture.

5. Types of stress • Compression: squeezing (convergent) • Tension: pulling apart in opposite directions (divergent) • Shearing: stress in opposite directions (transform)

7. Isostasy • The crust floats on the denser mantle • The gravitational balance of the crust is called isostasy • Isostatic adjustments occur when changes occur in the crust. • When weight is added to the crust it responds by subsiding or sinking • When weight is removed from the crust it responds by rebounding or moving upward

9. 11.2 Folds, Faults, and Mountains • Folds • Occur during mountain building • Form due to compression • Most occur in sedimentary rock • Bending of rocks • 3 main types: anticlines, synclines, and monoclines

10. Anticlines • Arching of rock layers • Form ridges • Synclines • Downfolds in rock layers • Sometimes called troughs • Form valleys • Anticlines and synclines are normally associated with each other.

12. Monoclines • Very broad folds • Large steplike folds • Found in areas that have faults

14. Faults • Movement along a fracture • The rock surface that is above the fault is called the hanging wall • The rock surface below the fault is called the footwall. • The area where movement is occurring is called the fault plane • Faults are classified according to the type of movement • There are 4 major types of faults: normal, reverse, thrust, and strike-slip

16. Normal • Occur due to tension • Hanging wall moves down relative to the footwall • Causes extension of the crust • Reverse and thrust • Occur due to compression • Hanging wall moves up relative to the footwall • Causes shortening of the crust • Strike slip • Occur due to shearing • Movement is horizontal

18. Types of Mountains • Folding and faulting produce many of Earth’s mountains • Mountains are classified by the processes that formed them. • Orogenesis: processes involved in mountain building • Groups of mountains • Range: group of similar mountains • System: a group of mountain ranges • Belts: large groups of mountain systems, most are found along the edges of continents

20. Folded Mountains • Form by folding due to compression • The Appalachians, Rockies, and Alps are examples • Sedimentary rocks are common • Volcanic Mountains • Form along plate boundaries and at hot spots • Contain igneous rocks • Aleutian Islands, Hawaii, Mid Ocean Ridge, Cascades

22. Fault Block Mountains • Form due to movement along normal faults • Formed by tension at a normal fault • The valleys formed are called grabens. • The uplifted areas are called horsts. • Sierra Nevada Mountains

25. Plateaus form when an area of the crust is uplifted vertically. Commonly contain sedimentary rock. • Domes are caused by bending upward of sedimentary layers. Commonly contain igneous and metamorphic rock.

26. 11.3 Mountains and Plates • Convergent Boundary Mountains • Most mountains form at convergent plate boundaries • Colliding plates produce compression • When subduction occurs, volcanic mountains commonly form on the overlying plate

27. Oceanic – Oceanic Convergence • Produce volcanic island arcs • Subduction zones and trenches form at the boundary • The more dense oceanic crust is subducted • Aleutian Islands • Oceanic – Continental Convergence • Produce continental volcanic arcs and folded mountains • Subduction zones and trenches form at the boundary • Oceanic crust is always subducted • Cascades, Rockies, and Andes

28. Continental – Continental Convergence • Folded mountains form • Both crusts will build up because continental crust is not dense enough to be subducted. • Himalayas and Appalachian

29. Divergent Boundary Mountains • Usually formed on the ocean floor • Forms the mid ocean ridge. • Divergent boundaries form fault block mountains • Volcanoes formed at a divergent boundary are called fissure or rift volcanoes • Non-Boundary Mountains • Hot spot volcanoes that form over a mantle plume • Hawaii

30. Continental Accretion • Accretion: occurs when material is scraped off of a subducted plate and combines with the land. • Enlarges continental land masses • Any crust that has become embedded into a continent is called a terrane. • Terranes have a geology that is different from the continent that it is attached to.