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Metamorphism and Metamorphic Rocks

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Presentation on theme: "Metamorphism and Metamorphic Rocks"— Presentation transcript:

1 Metamorphism and Metamorphic Rocks

2 Daily Question Correctly place the following
Igneous Rocks Contact Metamorphic Regional rocks Correctly place the following statements in the Venn Diagram. Occurs at divergent boundaries Occurs at convergent boundaries Forms as a result of melting (magma) Temperature is an agent Pressure is an agent Generates foliated rocks Forms as a result of being near an intrusion of magma Found in mountain belts May have been originally been a metamorphic rock Form at temperatures above 200 oC May underlie several adjacent states

3 Definitions Metamorphism – mineralogical, chemical, and physical changes that occur in solid rocks. Occurs at depths greater than that of lithification (Diagenesis). Solid state recrystallization – changes that occur without the rock melting (rocks that melt are igneous).

4 Factors influencing Metamorphism
Temperature Pressure Fluid Time Agents of Metamorphism


6 Factors influencing Metamorphism
Temperature below about 150oC, most minerals are stable (little or no metamorphism) above 150oC, reaction rate increases as temperature increases, new minerals begin to form above 600oC, some minerals begin to melt (transition to igneous rocks) Temperature a function of depth within the Earth and the presence of a magma

7 Factors influencing Metamorphism
Pressure as pressure increases, pore spaces reduced and density increases, pore fluids are expelled Minerals recrystallize and begin to realign Differential stress pressure is greater in one direction than in another

8 Temperature, Pressure and Rock Type


10 Effects of Stress Uniform Differential

11 Factors influencing Metamorphism
Pore fluids (water and carbon dioxide) as pressure increases, pore fluids are expelled Pore fluids increase the rate of metamorphic reactions by: storing ions involved in reactions moving ions from one place to another Chemical Fluids from Magmas Carry ions from the melt Fluids increase the temperature in the rock

12 Veins Solutions are deposited in fractures and joints

13 Factors influencing Metamorphism
Time solid state recrystallization is a slow process in general, size of minerals increases with time

14 Types of Metamorphism Burial Metamorphism 2. Contact Metamorphism
3. Regional Metamorphism

15 Metamorphism & Plate Tectonics

16 Types of Metamorphism Burial Metamorphism
most common type, occurs where crust is greater than 5 km thick Relatively low temperature and pressure (low grade metamorphism) Maximum stress vertical, foliation parallel to ground surface


18 Types of Metamorphism Contact metamorphism
Occurs in rocks around a magma body High temperature (heat from magma) “bakes” the rock around the magma creating an alternation High temperature & fluid primary agents, little to no pressure (occurs at shallow depths in the crust)

19 Non-foliated Metamorphic Rocks
Granular texture Interlocking grains Composed primarily of one mineral Uniform grain size

20 Contact Metamorphism

21 Contact Metamorphism

22 Types of Metamorphism Regional metamorphism
Large scale – large volume of rock is affected Associated with convergent plate margins and mountain building Folding and faulting increase thickness of the crust Occurs over a range of temperatures and pressures Fluids are also present Low grade to high grade metamorphism Will have zones of contact metamorphism

23 Regional Metamorphism

24 Metamorphic Grade


26 Metamorphic Grade As pressure and/or temperature increases, the grade of metamorphism increases

27 Low Grade Metamorphism
Example: Slate Rocks become more dense and compact forms at low temperature and pressure microscopic crystals dull luster clay and mica minerals foliated

28 Low Grade - Slate

29 Metamorphic Grade

30 Intermediate Grade Metamorphism
Example: Phyllite intermediate temperature and pressure small crystals shiny luster mostly mica minerals foliated

31 Intermediate Grade – Phyllite

32 Metamorphic Grade

33 High Grade Metamorphism
Example: Schist high temperature and pressure large crystals mica-rich foliated

34 High Grade - Schist

35 Metamorphic Grade

36 High Grade Metamorphism
Example: Gneiss high temperature and pressure large crystals mica-poor foliated

37 High Grade - Gneiss

38 Rock Cycle

39 Regional Revisited Slate Phyllite Schist, Gneiss Magma

40 Nonfoliated - Marble metamorphosed limestone (CaCO3)
bedding and fossils obliterated

41 Nonfoliated - Quartzite
metamorphosed quartz-rich sandstone Pore spaces filled with SiO2

42 Metamorphic Facies Different minerals form at different temperatures and pressures Group of stable minerals define a facies

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