GEO 101-007 Chapter 9 Notes
GEO 101-007 Chapter 9 Notes GEO 101-007
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This 6 page Class Notes was uploaded by Jennifer Gintovt on Sunday October 25, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 30 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 10/25/15
GEO 101007 10715 Chapter 9 Deformation Himalayan Mountains Mt Everest 29029 feet tall Mariana Trench 36070 feet tall 0 123 miles of elevation change 0 Earth s circumference 24901 miles Principles Key to Geologists Superposition the principle that younger layers of sediment are deposited on older layers of sediment thus a sequence of strata the oldest layer is at the base Original Horizontality the principle that sediments are deposited in nearly horizontal layers 0 Rocks found may include sandstone shale etc Tilted rock Foliated Rock 0 May include quartzite slate etc o Metamorphic rocks Faulted Rock Faulted Roc Review xx 39 2 93 quot 33quot I i J Normal fault ha r r y es 39 M vw 39 k Is this a normal or reverse fault gt hanging wall moving down is a NORMAL FAULTquotlt Mountain Rangesquot 0 Orogen orogenic belt a linear range of mountains 0 About a dozen globally numerous smaller ones Building Mountains Orogeny a mountain building event may last tens of millions of years Key Terms Uplift the upward vertical movement of the ground surface that occurs during mountain building Deformation a change in the shape position or orientation of a material by bending breaking or owing 1 Change in location displacement 2 Change in orientation rotation 3 Change in shape distortion oints naturally formed cracks fractures in rocks Faults a fracture on which one body of rock slides past another Folds a bend or wrinkle of rock layers folds form from a consequence of ductile deformation Strain The change in shape of an object in response to deformation ie 1 Stretching a Rock becomes longer 2 Shortening a Rock becomes shorter 3 Shear a Rock becomes tilted with change in angular relationships Brittle vs Ductile Deformation Brittle deformation the cracking and fracturing of a material subjected to stress chemical bonds break ceramic plate Ductile plastic deformation the bending and owing of a material without cracking or breaking subjected to a stress dough 0 New chemical bonds are quickly formed when old bonds break Factors Controlling Deformation Type Temperature warm rocks tend to deform ductilely while cold rocks tend to deform brittlely Pressure increased pressure causes more ductile deformation Higher pressure makes it harder for rock to separate into segments Deformation rate slow deformation rate allows for ductile deformation A sudden rate of deformation will act brittlely Composition some rocks are softer than others and are more capable of deforming ductilely Brittleductile transition Rocks at the Earth s surface 1015 km tend to have brittle behavior Rocks below this depth tend to have ductile behavior Boundary between brittle and ductile material is known as the brittle ductile transition Stress Stress Force applied per unit area Compression takes place when a rock is squeezed Tension occurs when a rock is pulled apart Shear stress develops when one side of a rock body moves sideways past the other side Pressure refers to a special stress condition in which the same push acts on all sides of an object Stress i Strain Stress causes strain change in shape Compression causes shortening Tension causes stretching Shear causes shear strain Pressure changes size of object but not shape joint i Fault Both joints and faults are cracks or fractures in rock but movement does not occur along a joint All faults are joints but not all joints are faults Faults Surfaces of Slip Reverse thrust and normal faults dipslip faultsquot Faults Surfaces of Slip more cartoons Reverse Transform Faults strikeslip faultsquot 0 Right or left lateral displacement lnF1lafnral Piohf lafnral Obliqueslip faults 0 A combination of dipslip and strikeslip displacement One block moves diagonally relative to the other Fault Scarp 0 Fault Breccia 0 Fault striations slickensides Fold Terminology Hinge Line portion of fold where curvature is greatest 0 m sides of folds show less curvature 0 Axial plane surface imaginary surface that cuts through hinges of multiple layers splits fold down the quotmiddlequot Anticline fold with archlike shape limbs dip away from hinge think quotAquot for anticline 0 Rock farthest out is youngest Axial plane V Hinge line Syncline Fold with throughlike shape limbs dip toward hinge think quotSquot for smile syncline Youngest rock is at the center Axial plane Anticlines and Synclines happen together Anticline Syncline Monocline Differential Weathering 0 What happens when different rocks in an outcrop undergo weathering at different rates based on resistance to weathering of material Dome 0 Fold with overturned bowl shape limbs dip away from center 0 Youngest rock is outer edge Basin 0 Fold with bowl shape limbs dip toward center Youngest rock is at the center Plunging Anticline If the hinge is horizontal the fold is called a nonplunging fold but if the hinge is tilted the fold is called a plunging fold anticline syncline Symmetrical vs Asymmetrical Folds Symmetrical folds go straight up and down 0 Asymmetrical folds have a more diagonal shape Overturned folds have an extreme diagonal shape Measuring deformed rocks How do we quantify how rocks deform in nature Geologists use the concept of strike and dip to describe orientation of structures in the field for mapping Measuring Dip The angle of inclination of a rock unit or fault measured from a horizontal plane Includes both a angle measurement ie how much its tilted and a direction ie which direction is it tilted Measuring Strike Perpendicular to dip The compass direction of the line produced by the intersection of a rock layer or fault with a horizontal plane Generally expressed as an angle relative to north measured clockwise Number typically is not shown Line of Horizontal plane strike v Strikedip 7 Q39Pltir6gtgrion 39 r 30 x4 i t F 39 I j 1 393 it w 4 r D39P angle 4539 o x 1 30 39 44 quot l gc uI I n l ki39 Water line gt a quotquot3 n c 1 j I o 5 4 J z liefiwr 39al39h r 1 v 39 4 lm 5334 u 4 41 39 p 39 39 39 gt Juc wquotu 13 quot quot I quotPf d pgqffl IL 0 alight l y t 1 d39o A ll 1 l m Jul 1 quot A wquot
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