Chapter 11 Deformation of the Crust Deformation Bending

Chapter 11 Deformation of the Crust

Deformation �Bending, tilting, and breaking of Earth’s crust

Isostasy �Equilibrium between lithosphere and asthenosphere �Gravity and buoyant forces in balance �Isostatic adjustment �Movement of lithosphere to reach isostasy

Isostasy Gravity Lithosphere Asthenosphere Isostatic adjustment Buoyancy

Isostatic Adjustments �Uplift �Mountains erode and become lighter �Uplifted by the asthenosphere

Isostatic Adjustment �Subsidence �Deposition increases weight �Lithosphere sinks into asthenosphere

Stress � Force exerted on a rock � Three types of stress 1. Compression – squeezing 2. Tension – stretching 3. Shear stress – pushing in opposite directions

Strain �Change in rock’s shape caused by stress �Depends on �Rock composition �Temperature �Pressure

Strain & Composition �Brittle composition �Respond by breaking or fracturing �Ductile composition �Respond by bending or deforming without breaking �High temp and pressure Ductile �Low temp & pressure Brittle

Brittle - Fractures

Ductile - Bending

Folds �Bend in rock layers resulting from stress �Three types �Anticline – oldest layer in center of fold �Syncline – youngest layer in center �Monocline – both limbs are horizontal

Anticline

Syncline

Monocline

Faults �Break in a body of rock along which one block moves relative to the other �Hanging wall �Wall of fault where a lantern would be hung �Foot wall �Wall of a fault where you would put your feet

Fault types �Normal fault �Hanging wall moves downward relative to footwall �Crust being torn apart

Fault Types �Reverse fault �Hanging wall moves upward relative to footwall �Crust being pushed together

Fault Types �Thrust fault �Hanging wall moves upward but at very low angle or nearly horizontal to footwall

Fault Types �Strike-Slip fault �Rocks on either side move horizontally in opposite directions �At transform boundaries

Mountains �Most extreme type of deformation �Mountain ranges �Adjacent mountains related to each other �Mount Everest part of Himalaya Range �Mountain Systems �Ranges make up systems �Great Smoky, Cumberland, Green make up Appalachian system �Mountain belts �Connected systems make belts

Tectonics & Mountains �Mountain belts on convergent plate boundaries �Mountains form when crusts (oceanic or continental) collide

Types of Mountains �Folded Mountains �Form when rock layers are squeezed together and uplifted �Also form plateaus – large, flat areas of rock high above sea level

Types of mountains �Fault block mountains �Faults break Earth’s crust into large blocks �Some blocks drop relative to others �Grabens – form when one block slips downward compared to 2 adjacent blocks (look like valleys) Graben

Death Valley, CA – a graben

Types of Mountains �Dome mountains �Circular structure made of rock layers that slope gently away from a central point

Types of Mountains �Volcanic Mountains �Formed when magma erupts onto Earth’s surface �Mid-ocean ridges �Cascade mountain range in Washington, Oregon and California