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Premium member Presentation Transcript Mountain Building : Mountain Building Rock Deformation Understanding the process : Understanding the process Every body of rock, no matter how strong, reaches a point where it can be bent or broken Deformation is a general term that refers to all changes in the original shape and/or size of a rock Most crustal deformation takes place along plate margins The forces that create the deformation are created by plate motions and interactions Understanding the process : Understanding the process Stress is the force per unit area acting on a solid (In physics, this is called “pressure”) When rocks are under stress that is greater than their own strength they begin to deform Deformations can be described as Folding Flowing Fracturing Understanding the process : Understanding the process If stress results in a change in the shape or volume of a rock, then it is called strain When stress is applied gradually, rocks deform elastically Elastic changes are recoverable. The rock can return to almost its original shape if the stress is gone (think of a rubber band) Once the elastic limit or strength is exceeded, the rock either flows or fractures These changes are inelastic and are not recoverable Understanding the process : Understanding the process What factors influence the strength of a rock and how it will deform? The temperature of the rock The confining pressure around the rock The type of rock The amount of time the stress is applied Understanding the process : Understanding the process Temperature and pressure influences Rock deforms permanently in two ways Brittle deformation Occurs near surface where temps and pressure is low Rocks behave like solids and fracture once strength is exceeded Comparative examples: glass, pencils, plates, etc Ductile deformation Occurs deep in the Earth where temps and pressure are high Produces a change in the size and shape of an object without fracturing it Comparative examples: clay, wax, caramel candy, a penny ran over by a train, etc Understanding the process : Understanding the process Rock type influences The mineral composition and texture of a rock also affects how it deforms Rocks with strong internal molecular bonds usually fail by brittle fracture Granite and basalt are good examples Sedimentary rocks that are weakly cemented or foliated metamorphic rocks are more likely to fail by ductile flow Rock salt, gypsum, shale, limestone, schist, marble of intermediate strength are good examples Understanding the process : Understanding the process Influence of time In nature, small stresses applied over a long period of time play an important role in deforming rock The force itself may be too small to deform the rock when it is first applied, but over time the rock will eventually give in and flow Marble benches are a good example. Old ones can be seen to sag under their own weight! Understanding the process : Understanding the process Types of stress There are three main types of stress Tensional stress Compressional stress Shear stress Understanding the process : Understanding the process Tensional stress Rocks are pulled in opposite directions along the same line Causes rocks to stretch, lengthen, break, or fracture Tension marks in a rock Understanding the process : Understanding the process Compressional stress Rocks are squeezed or shortened Causes changes the volume of the rock Understanding the process : Understanding the process Shear stress Forces are applied in different directions but not along the same line Causes rocks to become twisted or distorted Understanding the process : Understanding the process The buckling, twisting, pulling, compressing, etc of the land results in Folds Land that is bent into a series of wavelike ripples Faults Fractures in the crust along which movement has taken place Understanding the process : Understanding the process There are three main kinds of folds Anticlines Synclines Monoclines Understanding the process : Understanding the process Anticlines These are most commonly formed by the upfolding, or arching, of rock layers Understanding the process : Understanding the process Synclines Downfolds or troughs Often found with anticlines Understanding the process : Understanding the process Another difference between anticlines and synclines is found when they erode The oldest rocks are found in the center of eroding anticlines The youngest rocks are found in the center of eroding synclines Understanding the process : Understanding the process Monoclines Large, step-like folds in otherwise horizontal sedimentary strata Occur as sedimentary layers have been folded over large faulted block or underlying rock The monocline is shown as the overturned limb below Understanding the process : Understanding the process Capitol Reef National Park in Utah is a huge monocline called The Waterpocket Fold that extends for a hundred miles Understanding the process : Understanding the process Faults are fractures in the crust along which movement has ocurred. The two sides of a fault are the footwall and the hanging wall The footwall is the rock surface below the fault The hanging wall is the rock surface immediately above the fault Understanding the process : Understanding the process There are four main kinds of faults Normal faults Reverse faults Thrust faults Strike-slip faults Understanding the process : Understanding the process Normal Faults Occurs when the hanging wall block moves down relative to the footwall block Most have steep dips of about 60o Movement is mainly in a vertical direction with some horizontal movement Because of the downward motion of the hanging wall block, a normal fault results in the lengthening, or extension, of the crust Understanding the process : Understanding the process A Normal Fault Understanding the Process : Understanding the Process Reverse Fault The hanging wall block moves up relative to the footwall block Have dips (angles) greater than 45o Most are small Cause only local displacement Occur during compressional forces and result in a thickening and shortening of the rocks Understanding the process : Understanding the process Reverse Fault Understanding the process : Understanding the process Thrust Faults The hanging wall block moves up and over the footwall block Reverse faults with dips (angles) less than 45o Many sizes (small to as big as 50 km or more) Older rocks end up being on top of younger rocks Like a Reverse Fault, occurs as a result of compressional forces Understanding the process : Understanding the process Thrust Fault Understanding the process : Understanding the process Strike-slip Faults The movement of each side of the fault is horizontal and parallel to the fault surface Are large (the zone may be several kilometers wide) Linear valleys or troughs mark the location of these faults Are commonly caused by shear stress San Andreas Fault is a good example Understanding the process : Understanding the process Strike-slip Faults Understanding the process : Understanding the process Not all cracks or fractures in the Earth have had movement Fractures where no appreciable movement has occurred are known as joints. 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Part 1 Chap 11.1 Mnt Bldg McAlesterVince Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 46 Category: Education License: Some Rights Reserved Like it (0) Dislike it (0) Added: August 29, 2010 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Mountain Building : Mountain Building Rock Deformation Understanding the process : Understanding the process Every body of rock, no matter how strong, reaches a point where it can be bent or broken Deformation is a general term that refers to all changes in the original shape and/or size of a rock Most crustal deformation takes place along plate margins The forces that create the deformation are created by plate motions and interactions Understanding the process : Understanding the process Stress is the force per unit area acting on a solid (In physics, this is called “pressure”) When rocks are under stress that is greater than their own strength they begin to deform Deformations can be described as Folding Flowing Fracturing Understanding the process : Understanding the process If stress results in a change in the shape or volume of a rock, then it is called strain When stress is applied gradually, rocks deform elastically Elastic changes are recoverable. The rock can return to almost its original shape if the stress is gone (think of a rubber band) Once the elastic limit or strength is exceeded, the rock either flows or fractures These changes are inelastic and are not recoverable Understanding the process : Understanding the process What factors influence the strength of a rock and how it will deform? The temperature of the rock The confining pressure around the rock The type of rock The amount of time the stress is applied Understanding the process : Understanding the process Temperature and pressure influences Rock deforms permanently in two ways Brittle deformation Occurs near surface where temps and pressure is low Rocks behave like solids and fracture once strength is exceeded Comparative examples: glass, pencils, plates, etc Ductile deformation Occurs deep in the Earth where temps and pressure are high Produces a change in the size and shape of an object without fracturing it Comparative examples: clay, wax, caramel candy, a penny ran over by a train, etc Understanding the process : Understanding the process Rock type influences The mineral composition and texture of a rock also affects how it deforms Rocks with strong internal molecular bonds usually fail by brittle fracture Granite and basalt are good examples Sedimentary rocks that are weakly cemented or foliated metamorphic rocks are more likely to fail by ductile flow Rock salt, gypsum, shale, limestone, schist, marble of intermediate strength are good examples Understanding the process : Understanding the process Influence of time In nature, small stresses applied over a long period of time play an important role in deforming rock The force itself may be too small to deform the rock when it is first applied, but over time the rock will eventually give in and flow Marble benches are a good example. Old ones can be seen to sag under their own weight! Understanding the process : Understanding the process Types of stress There are three main types of stress Tensional stress Compressional stress Shear stress Understanding the process : Understanding the process Tensional stress Rocks are pulled in opposite directions along the same line Causes rocks to stretch, lengthen, break, or fracture Tension marks in a rock Understanding the process : Understanding the process Compressional stress Rocks are squeezed or shortened Causes changes the volume of the rock Understanding the process : Understanding the process Shear stress Forces are applied in different directions but not along the same line Causes rocks to become twisted or distorted Understanding the process : Understanding the process The buckling, twisting, pulling, compressing, etc of the land results in Folds Land that is bent into a series of wavelike ripples Faults Fractures in the crust along which movement has taken place Understanding the process : Understanding the process There are three main kinds of folds Anticlines Synclines Monoclines Understanding the process : Understanding the process Anticlines These are most commonly formed by the upfolding, or arching, of rock layers Understanding the process : Understanding the process Synclines Downfolds or troughs Often found with anticlines Understanding the process : Understanding the process Another difference between anticlines and synclines is found when they erode The oldest rocks are found in the center of eroding anticlines The youngest rocks are found in the center of eroding synclines Understanding the process : Understanding the process Monoclines Large, step-like folds in otherwise horizontal sedimentary strata Occur as sedimentary layers have been folded over large faulted block or underlying rock The monocline is shown as the overturned limb below Understanding the process : Understanding the process Capitol Reef National Park in Utah is a huge monocline called The Waterpocket Fold that extends for a hundred miles Understanding the process : Understanding the process Faults are fractures in the crust along which movement has ocurred. The two sides of a fault are the footwall and the hanging wall The footwall is the rock surface below the fault The hanging wall is the rock surface immediately above the fault Understanding the process : Understanding the process There are four main kinds of faults Normal faults Reverse faults Thrust faults Strike-slip faults Understanding the process : Understanding the process Normal Faults Occurs when the hanging wall block moves down relative to the footwall block Most have steep dips of about 60o Movement is mainly in a vertical direction with some horizontal movement Because of the downward motion of the hanging wall block, a normal fault results in the lengthening, or extension, of the crust Understanding the process : Understanding the process A Normal Fault Understanding the Process : Understanding the Process Reverse Fault The hanging wall block moves up relative to the footwall block Have dips (angles) greater than 45o Most are small Cause only local displacement Occur during compressional forces and result in a thickening and shortening of the rocks Understanding the process : Understanding the process Reverse Fault Understanding the process : Understanding the process Thrust Faults The hanging wall block moves up and over the footwall block Reverse faults with dips (angles) less than 45o Many sizes (small to as big as 50 km or more) Older rocks end up being on top of younger rocks Like a Reverse Fault, occurs as a result of compressional forces Understanding the process : Understanding the process Thrust Fault Understanding the process : Understanding the process Strike-slip Faults The movement of each side of the fault is horizontal and parallel to the fault surface Are large (the zone may be several kilometers wide) Linear valleys or troughs mark the location of these faults Are commonly caused by shear stress San Andreas Fault is a good example Understanding the process : Understanding the process Strike-slip Faults Understanding the process : Understanding the process Not all cracks or fractures in the Earth have had movement Fractures where no appreciable movement has occurred are known as joints.