Chapter 7 PM-1

Chapter 7 PM-1 - Geology 3443 Spring 2006 Chapter 7 Joints...

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Geology 3443 Spring 2006 Definitions and Distinctions 1. 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 2. 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 Surface Morphology 3. 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 4. What are the three modes of fracturing? – Mode I- sides move perpendicular to fracture Mode II- sides move parallel to fracture but perpendicular to fracture edge Mode III – sides move parallel to fracture and parallel to fracture edge Which mode produces joints?- Mode I fractures 5. How do columnar joints form? - they form from cooling lava where stress shadows determine spacing 6. What are the patterns that characterize the termination of joints and the intersection of joints? – Joint sets are the patterns, Orthogonal, conjugate, j joints, columnar
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Chapter 7 PM-1 - Geology 3443 Spring 2006 Chapter 7 Joints...

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