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# review for test - Chpt 7 review for test What is the...

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Chpt 7 review for test What is the difference between a) Fracture-narrow zone where in which cohesion of material is eliminated b) Joint- type of fracture that has no shear c) Shear fracture- small fault d) Fault-fracture that has shear displacement e) Vein- extensional fracture that has minerals precipated in the space What is the orientation of a joint relative to the stress principal directions at the time it formed?- parallel to maximum stress and perpendicular to minimum stress Does a joint have any shearing stress when it forms?- no What are the features that occur on the surfaces of joints, and what causes them?- Plumose structure forms because rocks are not homogenous and isotropic- this is because material properties of rock changes through out rock, stress filed at tip of cracks change as the cracks grow What is the difference between orthogonal and conjugate joints? –Orthogonal form perpendicular to each other (looks like bricks), conjugate forms an angle that is less than 90 degrees. A joint set and joint system? – Group of systematic joints, two or more joint sets Cross joints and non-systematic joints? Columnar and sheeting joints? – joints that form hexagonal shape because of cooling lava, joints that form because of schistisoty in rock that causes joints to form parallel to surface Explain how to tell the age relationship between two joint sets. What is hooking and why does it occur? – younger joints terminate at older joints, hooking is where younger joints curve into older joints What is a joint stress shadow? What how does it control joint spacing? What are the factors that control joint spacing? – area around joint where tensile stress has been reduced, length of joint and width of stress shadow since new joints can not form in stress shadows Explain how horizontal tension stress develops as rocks are uplifted and eroded (unroofed). Are the resulting joints horizontal or vertical in sedimentary rocks? – as stresses is reduced vertically the rock expands vertical only a little because nothing is bounding it and wants to contract horizontally because of cooling but can’t because it is locked in place by country rocks, this causes tensile stress to form, the resulting joints are vertical. Due to the Poisson effect which states that if a rock expands in on direction it must contract in the direction perpendicular to the expansion.

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Describe the factors that stop joints from growing.- stop from drop in fluid pressure,
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review for test - Chpt 7 review for test What is the...

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