DEFORMATION-OF-CRUST.pdf

1.Predict isostatic adjustments that will result from changes in the thickness of the earth’s crust. 2.Identify sources of stress in crustal rock.  The process of a material changing in shape or distorting, especially through the application of pressure. Plate tectonics is the m...

1.Predict isostatic adjustments that will result from changes in the thickness of the earth’s crust. 2.Identify sources of stress in crustal rock.  The process of a material changing in shape or distorting, especially through the application of pressure. Plate tectonics is the major c a u s e o f c r u s t a l deformation, but it is not the only force that shapes the earth’s crust.  E a c h r o c k t y p e deform differently when stress is gradually applied. Elastic deformation- rocks respond to stress. 1.Its either flows which we call ductile deformation. 2.It fractures in what we call brittle deformation. 1. The rock material must have the ability to deform under pressure and heat. 2. The higher the temperature of the rock, the more elastic it becomes. 3. Pressure must not exceed the internal strength of the rock, otherwise, fracturing occurs. 4. Deformation must be applied quickly. 1.Translated from its original position. 2.C h a n g e d i n orientation (folding, rotation or tilting) 3.Changed in shape (distortion)  Changes in the weight of some parts of the crust – Thicker and heavier = sink more deeply into the mantle – Thinner and lighter = rise higher on the mantle  Up-and-down movements of the crust occur because of two opposing forces. Crust presses down on the mantle Mantle presses up on the crust W h e n t h e t w o f o r c e s balance, the crust moves neither up nor down.  When weight is added to the crust, it sinks until a balance of the forces is reached again Balancing of the two forces is called ISOSTASY.  Up-and-down movements of the crust to reach isostasy is called ISOSTATIC ADJUSTMENTS As the adjustments occur, areas of the crust are bent up and down Pressure from this causes rocks in that area of the crust to deform.  Isostatic adjustments occur constantly: – Mountain ranges *As the crust becomes lighter, the region may rise. – Rivers flow into large bodies of water carrying large amounts of mud, sand, and gravel. *Added weight cause the floor to sink.  Isostatic adjustments occur constantly: – Glaciers once covered the land *Weight of the ice caused the crust underneath it to sink Glacial ice retreats Land slowly begins rising again in response to its reduced weight  Isostatic adjustment and plate movement cause stress in rocks that make up the earth’s crust. Amount of force per unit area that is placed on any given material  Pressure/Confining- a type of stress wherein the stress are all in the same direction If the stress is too much for the crust to handle, the crust can fracture from the inside. Compression - occurs when crustal rocks are squeezed together – often reduces the volume of the rocks  Tension - the force that pulls rocks apart – rocks tend to become thinner Shearing - sliding rocks past each other in opposite horizontal directions.  High pressure and temperatures caused by stress deform rocks. Stress applied slowly = rock may return to its original shape as the force is removed If the force exceeds an acceptable amount, the shape of the rock changes permanently Rock may also break because of extreme stress.  A fold is bending for rocks layers due to stress. Usually occurs deep in the crust where overlying rocks create great pressure so behavior is more plastic. Rock deformed without breaking.  There are three types of folds, Anticlines, Synclines and Monocline.  Anticline - Up-curved fold in which the oldest layer is in the center of the fold. - rock layers that slope downward on both sides of a crest. It resembles an “arch like”.  Syncline - Down-curved fold in which the youngest layer is in the center. - The rock layers that slope upward on both sides  Monocline - Simplest type of fold which involves a slight bend in otherwise parallel layers of rocks Gently dipping one way or the other  More complex fold types can develop in situations where lateral pressures become greater. Greater pressure results in anticline and synclines that are inclined and asymmetrical.  Fault is a fracture or zone of fractures between two blocks of rock. They are found in the boundaries of the tectonics plates. During the moving of the rocks, earthquakes also occur. Rock deformed by breaking.  Breaks in rocks when the rocks on either side of the break move is faulting. Breaks in rocks when the rocks on either side of the break do not move is fracture.  Fault plane - surface of a fault along which any motion occurs. Hanging wall - in a non- vertical fault, the rock above the fault plane. Footwall - rock below the fault plane.