Introduction to Metamorphic Rocks

1. Introduction to Metamorphic Rocks Metamorphism is the solid-state transformation of pre-existing rock into texturally or mineralogically distinct new rock as the result of high temperature,high pressure, or both.

2. Differential Pressure The Concept of Lithostatic Pressure

3. Which one is showing a banned structure?

4. The Concept of Geothermal Gradient Temperature increases with depth at a rate of 20-30oC/km in the crust. Temperature Moho Deep http://www.columbia.edu/itc/ldeo/v1011x-1/jcm/Topic3/Image1aa.gif

5. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the typical sequence formed by the prograde metamorphism of mudrocks slate, phyllite, schist and gneiss. Foliation  Minerals are Squished into bands.

6. 3 Types of Metamorphism Regional Metamorphism: Large-scale deformation associated with T and P

7. 3 Types of Metamorphism Contact Metamorphism: The main metamorphic agent is heat not pressure.

8. Which rock can be found with contact metamorphic rock?

9. 3 Types of Metamorphism Mylonite from shear zone in Appalachians Dynamic metamorphism: Rock deformation associated with fault zones

10. Metamorphic Facies and Grade Metamorphic facies: a set of metamorphic rocks characterized by particular mineral associations indicative of environment.

11. Spatial Distribution of Metamorphic Facies

12. Exercises –P64

13. Metamorphism of Sedimentary Rocks Protolith (Precursor) Sandstone: Quartzite, Metaquartzite Shale: Phyllite Slate Schist Gneiss Limestone: Marble

14. Progression of metamorphism Start with a shale and then hit it with pressure and heat. Slate Phyllite Schist

15. a: Slate b: Phyllite Slate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dull Foliated Metamorphic Rocks 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. Figure 22.1. Examples of foliated metamorphic rocks. a. Slate. b. Phyllite. Note the difference in reflectance on the foliation surfaces between a and b: phyllite is characterized by a satiny sheen. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

16. 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. Figure 22.1c.Garnet muscovite schist. Muscovite crystals are visible and silvery, garnets occur as large dark porphyroblasts. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

17. 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. Figure 22.1d.Quartzo-feldspathic gneiss with obvious layering. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

18. Banned structure You end up with something that is really Gneiss!

19. A foliation is any planar fabric in a metamorphic rock. In this case, the foliation is defined by aligned sheets of muscovite sandwiched between quartz grains. This slide is indicative of a phyllite. The foliation in this rock is a crenulation cleavage, and is developed after the horizonal foliation. This slide is indicative of a schist.

20. Specific Metamorphic Rock Types Marble: a metamorphic rock composed predominantly of calcite or dolomite. The protolith is typically limestone or dolostone. Quartzite: a metamorphic rock composed predominantly of quartz. The protolith is typically sandstone. Some confusion may result from the use of this term in sedimentary petrology for a pure quartz sandstone.

21. Which one is marble/limestone?

22. Which one is Quartzite/Sandstone?

23. Metamorphism of Igneous Rocks For most of our purposes, just put “meta” in front of the protolith name. Examples: metabasalt metarhyolite If a mafic or intermediate metamorphic rock is dominated by amphibole and feldspars: -Amphibolite.

24. Summary of metamorphic rocks

26. Metamorphic grade VS metamorphic rocks Composition and Temp Pressure and Temp

27. How does Metamorphism Relate to Plate Tectonics? T and P increase at collisional (convergent) plate boundaries.

28. Index minerals for Regional Metamorphism In regional metamorphic terranes, the temperature and pressure regime is indicated by the distribution of metamorphic minerals across a large area. Low metamorphic grade (low T and P; <200oC): Slate and phyllite: chlorite, muscovite, biotite Intermediate metamorphic grade Schist: garnet, staurolite, kyanite High metamorphic grade - 800 degrees C (verging on melting) Gneiss: kyanite, sillimanite Highest metamorphic grade: Partial melting Migmatite: rock partially melts, but no mass loss. Hence the mineralogy tells us the metamorphic grade of the rock.

29. Exercise –P67

30. Homework for Extra credit • 1 Strike and dip model • 2 True and apparent dip model • Apparent dip model • 3 point problem4 V-rule model • 5 Unconformity model6-7 Fault types • Normal fault model Reverse fault model Strike slip fault model Oblique normal fault model Oblique reverse fault model

31. 8-9 Faults displacing inclined bedsNormal faults and relay rampsCross-cutting normal faultsPlunging foldsFault-propagation and fault-bend fold Link: http://www.fault-analysis-group.ucd.ie/