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Deformation
Deformation, Mountain Building, and Earth's Crust
| Term | Definition |
|---|---|
| Deformation | any change in the shape of volume of a rock, such as when a rock is bolded (bended) or fractured (broken - joints/faults) |
| Force | is a push or a pull that causes change in motion |
| Stress | is a force of deformation applied over an area |
| Displacement | a volume of rock can be moved, or displaced, from one place to another, such as along faults |
| Rotation | a volume of rock can be rotated or titled in response to stress |
| Strain | any change in shape, size, or orientation of a volume of roc |
| Elastic Deformation/strain | occurs if rocks return to their original shape when the stress is release |
| Plastic Deformation/strain | happens when rocks fold or fracture when stress is applied and do not recover their original shape |
| Ductile | rocks show a great amount of plastic strain (they bend) before they fracture |
| Brittle | rocks fracture after only a small amount of plastic strain |
| Rock Behavior | - at shallow depths and low temperatures, most rocks are brittle and break - at greater depths, temperature and pressure are higher and rocks flow/bend as weak solids |
| Mineral Behavior | - at shallow depth and low temperatures, minerals may be unaffected - deeper and at higher temperatures, minerals may recrystallize or new minerals may grow |
| Compression | hortens the rock layers by folding or faulting |
| Tension | lengthens the rocks or pulls them apart; fractures and faults form - shallow levels: rocks fracture - deeper levels: rocks flow and stretch |
| Shear | deformation occurs along closely spaced planes like the slip between cards in a deck - shallow levels: rocks fracture - deeper levels: rocks flow and fold |
| Principle of Original Horizontality | says that most rocks are originally laid down flat |
| Principle of Superposition | says that rock layers on the bottom are older |
| Strike | intersection of a horizontal plane with an inclined plane |
| Dip | the maximum angle of an inclined plane |
| Geologic Structures | are rocks that have been deformed (including fracturing and/or folding) |
| Anticline | rock layers generally warped down - shaped like an A - oldest rocks in the center of fold |
| Syncline | rock layers generally warped up – shaped like an V - youngest rocks in the center of fold |
| Recumbent Folds | - axial plane is horizontal or nearly horizontal - usually form under compression at convergent boundaries |
| Domes | - layers that are uplifted in a circular or elliptical area and dip away in all directions - older rocks in center of dome - rock layers in age-position contexts the same as anticline |
| Basins | - folding and layers dip toward the center of basin from all directions - younger layers in center of basin - rock layers in age-position contexts the same as syncline |
| Monoclines | nearly flat layers bend down (dip) in one direction and then flatten out again |
| Joints | fractures along which no movement has taken place parallel to fracture surface, although movement may occur perpendicular to the surface. they are not faults. |
| Faults | fractures along which the opposite sides have moved relative to one another and parallel to the fracture |
| Dip-slip Faults | all movement is in the direction of dip (up or down) along dip-slip faults - normal: from tension - reverse/thrust: from compression |
| Normal Dip-slip Faults | from tension - hanging wall moves down relative to the footwall |
| Reverse Dip-slip Fault | from compression - hanging wall moves up relative to footwall |
| Thrust Dip-slip Fault | a type of reverse fault that dips at less than 45°, often as low as 5 |
| Strike-slip Faults | move with a side-to-side motion, parallel to the strike of the fault - not up or down - classified as right-lateral or left-lateral, depending on the apparent direction of the offset between blocks |
| Strike-slip Faults | two sides move horizontally relative to one another |
| Mountains | an area of land that stands at least 300m above the surrounding country and has a restricted summit area |
| Mountain Range | a group of linear peaks and ridges that formed together |
| Mountain System | a complex group of linear peaks and ridges that is composed of several mountain ranges |
| Mountain Building | mountain building involves faulting and folding but can arise without these types of deformation |
| Orogeny | an episode of mountain building |
| Continental Accretion | a process of adding material to a continent |
| Terranes | exotic pieces, fragments of seamounts, or small pieces of continents that get transported on the plates |
| Principle of Isostacy | Earth’s crust “floats” on the denser mantle |
| Isostatic Rebound | when large glaciers melt or mountains erode away, the crust rises back up to its equilibrium level |
Created by:
user1115
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