This document discusses metamorphism, which is the transformation of one rock type into another through heat, pressure, and chemical changes. Metamorphic rocks are formed from pre-existing igneous, sedimentary, or other metamorphic rocks. Metamorphism can occur at various depths in the crust and upper mantle. It leads to changes in mineral content, texture, and chemical composition of the original rock. The degree of metamorphism ranges from low-grade to high-grade. Heat sources within the Earth include primordial heat, radioactive decay, and solar radiation. Pressure agents are confining pressure and differential stress. There are different types of metamorphic environments and textures that form.

2. Parent rock – origin of a metamorphic rockSee next slides for samples of metamorphic rocks

3. Norway

4. China

5. Lake Huron, Ontario, Canada

6. Michigan, North America

7. California, North America

8. California, North America

10. Texture

12. Pressure

15. High-grade metamorphism : identity of parent rock becomes hard to distinguish

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

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.

24. Radioactivity – energy released when subatomic particles are spontaneously emitted by radioactive elements

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.

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.

37. degrees of metamorphism

39. regional metamorphism

41. Contact metamorphism

42. Contact metamorphism

43. Contact metamorphism

44. Contact metamorphism Granite Gneiss

45. From limestone to marble

46. From igneous rocks to marble Syenite (igneous) marble

47. From sediments to metamorphic rocks

49. directional stresses are involved

52. Regional metamorphism

53. Regional vs contact metamorphism

57. schistosity – larger crystals

59. Rock or Slaty cleavage

60. Rock or Slaty cleavage

61. Schistocity mica schist – most abundant schist type

62. Schistocity mica schist

63. Schistocity

64. Schistocity

65. Schistocity

66. Schistocity

67. Schistocity talc schist

68. Schistocity talc schist

69. Schistocity talc schist

70. Gneissic texture

71. Gneissic texture

72. Gneissic texture

73. Gneissic texture

74. Nonfoliated texture marble

75. Nonfoliated texture

76. Nonfoliated texture

77. Nonfoliated texture

78. Nonfoliated texture quartzite

79. Nonfoliated texture quartzite