1. Metamorphism: New Rocks from Old
Chapter 10
Geology Today
Barbara W. Murck, Brian J. Skinner
Disharmonic Folding in Gneiss
N. Lindsley-Griffin, 1999

2. Rock Cycle Metamorphic Rock
Rock formed in the solid state by alteration of preexisting rock deep within the Earth.
Heat, pressure, and chemically active fluids are the agents.
J. R. Griffin, 1999

3. Metamorphism
Mineralogical, chemical, and structural changes in solid rocks, in response to physical and chemical conditions at depths below regions of sedimentation and diagenesis.
Fig. 10.2, p. 273
N. Lindsley-Griffin, 1999

4. Pressure, temperature are the most important factors.
Metamorphism
Pressure, temperature are the most important factors.
N. Lindsley-Griffin, 1999

5. Metamorphic Factors PORE FLUIDS
Small amounts of gases or liquids between grains
Facilitate solution, migration, and precipitation of ions to speed up recrystallization
Provide a reservoir for ions during the growth of new minerals
Speed up reactions
Fig. 10.3, p. 274
Quartz veins in slate
N. Lindsley-Griffin, 1999

6. Metamorphic Factors PRESSURE 1. Confining pressure:
greater density, prevents fracture, plastic deformation
2. Differential stress: Non-uniform pressure produces
preferred orientation, rock cleavage, foliation
Fig. 10.4, p. 275:
Granite formed in uniform stress
Gneiss formed in differential stress
N. Lindsley-Griffin, 1999

7. Metamorphic Factors HEAT Enhances recrystallization
Speeds up chemical reactions
At deepest crustal levels, some of the rock melts
Migmatite - part metamorphic and part igneous
(Fig. 10.9, p. 281)
N. Lindsley-Griffin, 1999

8. Slate Gneiss Protolith: shale Protolith: shale Low grade High grade
Metamorphic Factors
TIME - enhances all other metamorphic factors Long periods of time allow larger grains to grow
Slate Gneiss
Protolith: shale Protolith: shale
Low grade High grade
N. Lindsley-Griffin, 1999

9. Metamorphic Factors LARGE AMOUNTS OF FLUIDS = METASOMATISM
Composition changes greatly by:
- addition of new material
- removal of old material
- combination of both
Fig , p. 291:
Limestone changed into
red garnet, green pyroxene,
and calcite rock.
If pure, would be marble.
N. Lindsley-Griffin, 1999

10. Metamorphic Factors LARGE AMOUNTS OF FLUIDS = METASOMATISM
Composition changes greatly by:
- addition of new material
- removal of old material
- combination of both
Fig , p. 291:
Limestone changed into
red garnet, green pyroxene,
and calcite rock.
If pure, would be marble.
N. Lindsley-Griffin, 1999

11. Preferred orientation:
All the seagulls are facing into or away from the wind
This alignment produces a foliation
N. Lindsley-Griffin, 1998

12. Foliation:
From conglomerate to metaconglomerate - flattened cobbles parallel to each other
Alluvial sandstone and conglomerate
Metaconglomerate, Fig. 10.5, p. 276
N. Lindsley-Griffin, 1998

13. Foliation:
Slaty cleavage - tendency to break along planes that form perpendicular to maximum stress.
In folded layers the cleavage parallels the axial plane
Slaty cleavage at angle to bedding
Fig. 10.7, p. 277
N. Lindsley-Griffin, 1999

14. Foliation:
Schistosity - planar minerals like mica crystallize perpendicular to maximum stress.
Garnet Schist
Thin section view of schistosity in phyllite
N. Lindsley-Griffin, 1999

15. Foliation:
Gneiss - micaceous schist alternating with coarsely crystalline bands
Pre-existing layers
High-grade metamorphism
N. Lindsley-Griffin, 1999

16. Low Grade to High Grade
Progressive changes to shale as higher T and P over time allow different index minerals to form.
Fig. 10.8, p. 280
N. Lindsley-Griffin, 1999

17. Types of Metamorphism CONTACT METAMORPHISM
Rocks are heated and chemically changed by intrusion of hot magma.
Concentric zones or aureoles
N. Lindsley-Griffin, 1999

18. Types of Metamorphism BURIAL METAMORPHISM - Deep sedimentary basins
REGIONAL METAMORPHISM - Subduction
and plate collision; most intense where continents collide
Affects broad regions
Mountain ranges and
continental interiors
Fig , p. 283
N. Lindsley-Griffin, 1999

19. Types of Metamorphism METASOMATISM Very large water-rock ratios
Composition changes greatly by:
- addition of new material
- removal of old material
- combination of both
Fig , p. 291:
Limestone changed into
red garnet, green pyroxene,
and calcite rock.
If pure, would be marble.
N. Lindsley-Griffin, 1999

20. Metamorphic Facies
INDEX MINERAL - appears at certain P-T conditions in the progression from lower grade to higher grade:
Chlorite
Biotite
Garnet
Kyanite
Sillimanite
ISOGRADS - lines on map showing where a particular index mineral first appears.
Fig , p. 284
N. Lindsley-Griffin, 1999

21. Assemblage of minerals typical of a set of metamorphic conditions
Metamorphic Facies
Assemblage of minerals typical of a set of metamorphic conditions
Fig , p. 285
N. Lindsley-Griffin, 1999

22. Polymorphs of Al2SiO5 reveal P-T conditions
Metamorphic Facies
Polymorphs of Al2SiO5 reveal P-T conditions
Kyanite
Sillimanite
Andalusite
Fig , p. 285, with additions
N. Lindsley-Griffin, 1999

23. Continental core regions -- Canadian Shield
Regional metamorphism
Continental core regions --
Canadian Shield
N. Lindsley-Griffin, 1998

24. Finely foliated rocks: slate and phyllite.
Regional metamorphism
Finely foliated rocks: slate and phyllite.
Slate, with slaty cleavage at high angle to bedding
N. Lindsley-Griffin, 1998

25. Coarsely foliated rocks: Schist
Regional metamorphism
Coarsely foliated rocks: Schist
Micaceous minerals, formed from shale or siltstone
N. Lindsley-Griffin, 1998

26. Coarsely foliated rocks: Gneiss
Regional metamorphism
Coarsely foliated rocks: Gneiss
Bands of micaceous minerals alternating with bands of granular minerals (usually quartz and feldspar)
N. Lindsley-Griffin, 1998

27. Shear Metamorphism
Along faults - grinding and crushing at shallow crustal levels,
stretching and recrystallization at deeper levels. Also known as cataclastic metamorphism (not in textbook).
Mylonite Thin section
N. Lindsley-Griffin, 1998

28. Protolith + Process = Product
Metamorphic Rocks
Foliated
Protolith Process = Product
Greenschist
Amphibolite
Basalt + moderate T and P = greenschist (green chlorite)
Basalt + high T and P = amphibolite (black amphibole)
Fig , p. 288
N. Lindsley-Griffin, 1999

29. Protolith + Process = Product
Metamorphic Rocks
Foliated
Protolith Process = Product
Basalt + low T, high P = Blueschist (blue amphibole)
Blueschist + high T and P = Eclogite (green pyroxene, red garnet)
(Fig , p. 288)
N. Lindsley-Griffin, 1999

30. Protolith + Process = Product
Metamorphic Rocks
Foliated
Protolith Process = Product
Shale Slate Phyllite Schist, Gneiss
Increasing metamorphic grade
Fig. 10.8, p. 280
N. Lindsley-Griffin, 1999

31. Protolith + Process = Product
Metamorphic Rocks
Foliated
Protolith Process = Product
Shale + heat, pressure Slate Phyllite
with progressive growth of foliation, grain size
(Fig , p. 287)
N. Lindsley-Griffin, 1999

32. Protolith + Process = Product
Metamorphic Rocks
Foliated
Protolith Process = Product
Phyllite Schist (clay-rich)
Gneiss (quartz + feldspar rich)
N. Lindsley-Griffin, 1999

33. Protolith + Process = Product
Metamorphic Rocks
Nonfoliated
Protolith Process = Product
Hand specimen of Quartzite
Thin section of Quartzite
Quartz sandstone + Recrystallization = Quartzite
Fig , p. 290
N. Lindsley-Griffin, 1999

34. Protolith + Process = Product
Metamorphic Rocks
Nonfoliated
Protolith Process = Product
Thin section of Marble
Hand specimen of Marble
Limestone Recrystallization = Marble
Fig , p. 290
N. Lindsley-Griffin, 1999

35. Metamorphic Facies at Convergent Boundaries
High temperature,
low pressure
in volcanic arcs
Greenschist and Amphibolite facies
High pressure,
low temperature
in subduction zone
Greenschist and
Blueschist facies
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36. Metamorphism at Convergent Boundaries
Regional
Contact
Shear
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37. Metamorphism at Mid-Ocean Ridges
Sea water circulates
in fractures
Water is heated,
hydrothermally
changes basalt
Metals are
concentrated
near hot vents
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38. Metamorphism at Divergent and Transform Boundaries
Shear
Divergent:
Hydrothermal
Shear
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