Mountain Building Earth Science Ch. 11

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.

At the surface Inside the earth Temperature and pressure are low Rocks fold and fracture Inside the earth Temperature and pressure are high Folding and fracturing do not occur

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.

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

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

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

Anticlines and synclines are normally associated with each other. 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.

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

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

Normal Reverse and thrust Strike slip 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

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

Folded Mountains Volcanic 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

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

Plateaus form when an area of the crust is uplifted vertically 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.

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

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 Oceanic crust is always subducted Cascades, Rockies, and Andes

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

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

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.