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.

1. Metamorphism – transformation of one rock type into another Metamorphic rocks – produced from pre-existing sedimentary, igneous and metamorphic rocks

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

9. Metamorphism leads to changes in: Mineral content

10. Texture

11. Chemical compositionMetamorphic agents are: Heat

12. Pressure

13. Chemically active fluidsMetamorphism occurs from a few km into the crust all the way down to the upper mantle.

14. Degrees of metamorphism Low-grade metamorphism : little change in the parent rock

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

16. Remember : parent rock should not melt, if it does, then igneous processes (not metamorphic) become involvedExample of low-grade metamorphism (from shale to slate)Shale (sedimentary rock)Slate (metamorphic rock)

17. Example of high-grade metamorphism: from shale (top) to slate (top right) to gneiss (right)

18. Degrees of metamorphismAgents of metamorphismTimelow-gradeLOWSHORTHeatPressureChemical activityHIGHhigh-gradeLONG

19. Heat as an agent of metamorphismHeat provides the energy of activation for the chemical transformation in metamorphic rocks.Chemical reactions result in:recrystallization of existing minerals

20. formation of new minerals Chemical changes are all based on the increased kinetic energies of the ions.

21. Heat as an agent of metamorphismTemperatures 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 worldThe 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.

23. What heats up the Earth? Primordial heat – trapped when Earth’s crust first cooled

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

25. Solar radiation – absorbed and converted to thermal energy by the Earth’s surfacePrimordial heatEarth initially formed as a molten ball of rock. When the surface cooled to become the crust, the heat became trapped.This trapped heat now drives the convection cells in the mantle and the movement of the molten outer core round the inner core.

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. RadioactivityRadioactive 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.

29. Pressure as an agent of metamorphismTwo types of pressure: Confining pressure – experienced by buried rocks; forces are applied equally in all directions

30. Differential stress – forces are unequal in different directionsConfining pressure is evenly distributed. squeezes out the spaces between mineral grains

31. produces a more compact, denser rockConfining pressure produces rock layers that are undeformed.

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 pressureHeat increases with increasing pressure. This means that areas of mountain building (continental vs continental convergent plates) are hotter due to greater pressure.

36. METAMORPHIC ROCKS definition

37. degrees of metamorphism

38. agents of metamorphismWhere does metamorphism occur? contact metamorphism

39. regional metamorphism

40. dynamic metamorphismContact metamorphism

41. Contact metamorphism

42. Contact metamorphism

43. Contact metamorphism

44. Contact metamorphismGraniteGneiss

45. From limestone to marble

46. From igneous rocks to marbleSyenite(igneous)marble

47. From sediments to metamorphic rocks

48. Regional metamorphismMountain-building: plate tectonics (convergent boundaries)

49. directional stresses are involved

50. greatest volume of metamorphic rocks are produced in this wayReview of plate tectonics

52. Regional metamorphism

53. Regional vs contact metamorphism

54. Textural changesTexture – size, shape, and distribution of particles that constitute a rock foliated

55. non-foliatedTextural changes (foliation)

56. Types of foliation: rock or slaty cleavage – minute crystals

57. schistosity – larger crystals

58. gneissic texture – segregation of mineralsRock or Slaty cleavage

59. Rock or Slaty cleavage

60. Rock or Slaty cleavage

61. Schistocitymica schist – most abundant schist type

62. Schistocitymica schist

63. Schistocity

64. Schistocity

65. Schistocity

66. Schistocity

67. Schistocitytalc schist

68. Schistocitytalc schist