Chapter 11 Plate Tectonics

I. Deformation- the bending, tilting or breaking of Earth’s crust I. Deformation- the bending, tilting or breaking of Earth’s crust -Virginia’s Appalachian Mountains are example

II. Isostasy- balance between force of gravity pushing lithosphere down and the buoyant of the asthenosphere pushing up Think of the Asthenosphere as a sponge Think of the lithosphere as a weight on the sponge a. If the mass of the weight is decreased, the sponge expands b. If the mass of the weight is increased the sponge compresses c. The forces on change slowly, but in the same way

III. Stress- the amount of force per unit area (example- pounds per square foot) Compression- squeezing and shortening Tension- pulling and stretching Shear Stress- pushing parts of crust on different directions

IV. Strain- any change in shape or volume that is caused by stress A. Permanent Stress Brittle- materials that respond to stress by cracking or breaking ductile- materials that respond to stress by bending or deforming without breaking

The composition of the rock determines whether it is ductile or brittle Temperature and pressure determine whether rock is ductile or brittle 1. Rock near Earth’s surface is more likely to be brittle 2. Under surface, the rock is exposed to higher temps and pressure. There it is more likely to be ductile.

B. Temporary Strain- rock deforms then goes back to its original shape when stress is removed

V. Folds- a bend in the rock layer A. When rock responds to stress in a ductile way, folds are created. 1. Anticlines: a fold in which the oldest layer is in the center of the fold Oldest

2. Syncline: a fold in which the youngest rock is in the center of the fold

3. Monocline: a fold where the limbs are horizontal, but one limb has moved up

VI. Faults- a break in the rock layers caused by stress in brittle rock A. Size: 1. Can be a few layers of rock in a small region 2. Can be thousands of kilometers long Fracture Hanging Wall Foot Wall

B. Normal fault- a fault in which the hanging wall moves down

C. Reverse fault- a fault in which the hanging wall is pushed up

C. Strike Slip Fault- a fault in which the walls slide past each other horizontally

I. Mountain Ranges and Systems A. Mountain Ranges: groups of mountains in the same region that are the same age, structure and shape B. How Mountains form: 1.Plate Collisions

i. Oceanic crust meets Continental Crust Oceanic crust flows under continental crust ·Oceanic trenches are formed ·Friction of subducting plate heats up material above it and cause magma to form producing volcanic mountains on the over- riding plate Volcanic Mountains Trench

ii. Continental crust meets continental crust Folded Mountains ii. Continental crust meets continental crust crusts are about the same density, so neither subducts crusts crumple and lift up forming high, folded mountain chains such as the Appalachian mountains Plateaus are also formed

iii. Oceanic crust meets oceanic crust the denser crust subducts mantle rock is melted, creating magma ·Forms underwater volcano chains ·Appear above water’s surface as island arc volcanoes

iv. Continental Growth -Terranes “get stuck” to existing continents ·most present day continents are made of cratons” (old, stable rocks) with some terranes are identified by rocks and minerals different from the rest of a continent -Terranes can be small sea mounts or large chunks of continental crust