1. Metamorphic Rocks

2. Metamorphic Rocks Metamorphism:
The transition of one rock into another in the solid state under conditions unlike those under which it formed
Metamorphic rocks are produced from:
Igneous rocks
Sedimentary rocks
Other metamorphic rocks

3. Agents of Metamorphism
Heat- The most important agent
Recrystallization results in new, stable minerals
Two sources of heat
Contact metamorphism – heat from magma
Regional Metamorphism - increase in temperature with depth due to the geothermal gradient

4. Agents of Metamorphism
Pressure
Increases with depth
Confining pressure applies forces equally in all directions
Rocks may also be subjected to differential stress which is unequal in different directions and causes deformation

5. Agents of Metamorphism
Pressure

6. Types of Metamorphism Contact metamorphism
From Understanding Earth, Press and Siever. Freeman.
Contact metamorphism

7. Regional metamorphism
Types of Metamorphism
Regional metamorphism

8. Regional metamorphism
Types of Metamorphism
Regional metamorphism
More Uplift

9. Regional metamorphism
Types of Metamorphism
Regional metamorphism
From Understanding Earth, Press and Siever. Freeman.

10. Metamorphic Textures
Foliation - any planar arrangement of features within a rock
Foliation can form in various ways:
Rotation of platy and/or elongated minerals
Recrystallization of minerals in the direction of preferred orientation
Changing the shape of equidimensional grains into elongated shapes that are aligned

11. Metamorphic Textures
Foliation can form in various ways:

12. Metamorphic Textures Foliated textures Slaty cleavage
Closely spaced planar surfaces along which rocks split

13. Metamorphic Textures Foliated textures Schistosity
Platy minerals are discernible with the unaided eye and exhibit a planar or layered structure
Rocks having this texture are referred to as schist

14. Metamorphic Textures Foliated textures Gneissosity
During higher grades of metamorphism, ion migration results in the segregation of minerals into layers
Gneissic rocks exhibit a distinctive banded appearance

15. Metamorphic Textures
Metamorphic rocks that lack foliation are referred to as non-foliated
Develop in environments where deformation is minimal
And/or composed of minerals that exhibit equidimensional crystals
General name is granofels

16. Metamorphic Rocks Foliated Metamorphic Rocks a b
Slate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dull
Phyllite: a rock with a schistosity in which very fine phyllosilicates (sericite/phengite and/or chlorite), although rarely coarse enough to see unaided, impart a silky sheen to the foliation surface. Phyllites with both a foliation and lineation are very common.

17. Metamorphic Rocks Foliated Metamorphic Rocks
Schist: a metamorphic rock exhibiting a schistosity. By this definition schist is a broad term, and slates and phyllites are also types of schists. In common usage, schists are restricted to those metamorphic rocks in which the foliated minerals are coarse enough to see easily in hand specimen.

18. Metamorphic Rocks Foliated Metamorphic Rocks
Gneiss: a metamorphic rock displaying gneissose structure. Gneisses are typically layered (also called banded), generally with alternating felsic and darker mineral layers. Gneisses may also be lineated, but must also show segregations of felsic-mineral-rich and dark-mineral-rich concentrations.

19. Metamorphic Rocks Specific Metamorphic Rock Types
Marble: a metamorphic rock composed predominantly of calcite or dolomite. The protolith is typically limestone or dolostone.

20. Metamorphic Rocks Specific Metamorphic Rock Types
Quartzite: a metamorphic rock composed predominantly of quartz. The protolith is typically sandstone.

21. Metamorphic Rocks
Greenschist/Greenstone: a low-grade metamorphic rock that typically contains chlorite, actinolite, epidote, and plagioclase. Such a rock is called greenschist if foliated, and greenstone if not. The parent is either a mafic igneous rock or graywacke.

22. Metamorphic Rocks Specific Metamorphic Rock Types
Amphibolite: a metamorphic rock dominated by hornblende + plagioclase. Amphibolites may be foliated or non-foliated. The parent is either a mafic igneous rock or graywacke.