17. Example of high-grade metamorphism: from shale (top) to slate (top right) to gneiss (right)
18. Degrees of metamorphism Agents of metamorphism Time low-grade LOW SHORT Heat Pressure Chemical activity HIGH high-grade LONG
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20. formation of new minerals Chemical changes are all based on the increased kinetic energies of the ions.
21. Heat as an agent of metamorphism Temperatures increase with depth at a rate known as the geothermal gradient. Hence, degree of metamorphism increases as depth increases.
22. The deepest mine in the world The Western Deep Levels Mine in South Africa at 4 km is the deepest in the world. At these depths, the rock is actually hot enough to burn human skin. Miners work in pairs- one digging, the other operating a large fan to keep cool.
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24. Radioactivity – energy released when subatomic particles are spontaneously emitted by radioactive elements
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26. Solar radiation – the Earth’s crust absorbs about 50% of the Sun’s energy
27. The absorbed solar radiation is distributed unevenly. The greatest concentration occurs in the tropical belt (red zone).
28. Radioactivity Radioactive elements contribute to Earth’s internal heat. Background radiation (not enough to harm) exists all around us. Shown at right is a geologist measuring background radiation with a portable Geiger counter.
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32. Directonial stress deforms rock layers as shown in C. (the series shows the deformation of sediments deposited in a river flood plain)
33. The layers of rock shown below have been deformed by directional stress. Such pressure is most active in convergent plate boundaries.
34. Rocks in shallow depths are pulverized when subjected to differential stress. At greater depths, on the other hand, rocks are more ductile and are compressed and elongated rather than crushed. A sample of conglomerate becomes metaconglomerate when subjected to differential stress at depth (note the elongated rock fragments).
35. Heat and pressure Heat increases with increasing pressure. This means that areas of mountain building (continental vs continental convergent plates) are hotter due to greater pressure.
![Metamorphism – transformation of one rock type into another ,[object Object]](https://image.slidesharecdn.com/metamorphism-101202032403-phpapp01/85/Metamorphism-1-320.jpg)
