Deformation and Metamorphism

More documents

Recommendations

Info

1.3 – Regional Processes 1.3.3 – Deformation BENDING OR BREAKING Forces (or pressure) acting on rocks may cause deformation, which is likely to take one of two forms — bending or breaking. In response to the forces acting on it, the undeformed strata shown in the adjacent diagram may either: bend to form folds, or break to form joints. FACTORS AFFECTING NATURE OF DEFORMATION 1. Pressure The pressure acting on a rock mass is likely to be a combination of load pressure, due to the weight of overlying rocks, and directed pressure caused by forces within Earth's crust. Load pressure acts equally in all directions, merely compressing the rock. By contrast, directed pressure squeezes the rock in only one direction. Deformation of rocks is caused by directed pressure but the load pressure affects the nature of the deformation. If the load pressure is low, directed pressure is likely to cause the rocks to fracture. If the load pressure is high, the rocks are more likely to bend under the influence of directed pressure. Rocks deep within the crust are therefore likely to fold, while those closer to the surface are more likely to break. Topics 1.3.3 & 1.3.4 Deformation & Metamorphism Page 4 of 33
2. Temperature Changes in temperature affect the way in which rocks behave when subjected to stress. At higher temperatures, folding is more likely to occur than breaking. This is another reason why folding usually occurs deep below Earth's surface, whereas breaking occurs closer to the surface. 3. Fluids Fluids which are present in the pore spaces of rocks and joints, act as lubricants, making is easier for rock layers to slide over each other. Thus the presence of fluids makes it more likely that the rocks will bend rather than break. 4. Time Solid, brittle materials normally bend rather than break if they are deformed very slowly. Small forces applied over very long periods of time may cause rocks to deform by a process called creep. This can be observed in old buildings, where floor boards and marble mantelpieces may sag. JOINTS & FAULTS Joints and faults are formed at or near Earth's surface when sudden forces act (e.g. earthquakes). When rock fractures a joint is formed. A fault is created if the rocks on one side of the joint move relative to rocks on the other side The terms associated with faults are shown in the adjacent diagram. Learn all these terms and their meanings (i.e. footwall, fault scarp, hanging wall) Topics 1.3.3 & 1.3.4 Deformation & Metamorphism Page 5 of 33
Page 1 and 2: Student: ……………………
Page 3: Regional Processes Metamorphism Met
Page 7 and 8: (Tightly) folded rock formation at
Page 9 and 10: 1.3 - Regional Processes 1.3.4 - Me
Page 11 and 12: THERMAL (CONTACT) METAMORPHISM Ther
Page 13 and 14: Over many millions of years, two co
Page 15 and 16: Orogenic activity, and hence region
Page 17 and 18: Foliated Rocks As shown in the diag
Page 19 and 20: Both the original bedding planes an
Page 21 and 22: 3. Use the table below to summarise
Page 23 and 24: 9. Label the adjacent diagram, whic
Page 25 and 26: Factors Affecting Metamorphism 1. I
Page 27 and 28: 4. What can you say about the relat
Page 29 and 30: Regional Metamorphism 1. Describe,
Page 31 and 32: 7. a. Give the words that are used
Page 33: 11. Summarise the characteristics o

Deformation and Metamorphism

Create successful ePaper yourself

Delete template?

Save as template?