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Metamorphic Rocks

Metamorphic Rocks

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Metamorphic Rocks

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  1. Metamorphic Rocks Evidence of metamorphism The ingredients of metamorphism Prograde metamorphism of shale Classification of Metamorphic Rocks Metamorphism and Plate Tectonics

  2. Metaphoric Rocks • These are ricks that have changed (meta) their form (morphic). • Under the influence of heat, pressure and fluids, pre-existing rocks are modified in form and even in internal atomic structure to produce new rocks stable at the new conditions. • This is done within the solid state, i.e. without melting. • Changes that occur include: • increase in grain size, • new minerals • foliation (parallel alignments).

  3. Formation of Metamorphic Rocks • 1. Parent Rock • Even though minerals will change most elements are provided by parent rock except water and some dissolved ions Shale Schist

  4. Formation of Metamorphic Rocks Temp. (ºC) 0 C 600 1200 A B • 2. Increased Temperature (geothermal gradients) • Minerals stable at lower temperatures converted to minerals stable at higher temperatures. • Solid state chemical reactions are accelerated A B C

  5. Ingredients of Metamorphism • 3. Increased Pressure (and stresses) • Increased Confining Pressure as rocks are buried • Compression at convergent plate boundary or Sheared as plates slide past each other

  6. Ingredients of Metamorphism • 4. Addition or removal of fluids (and elements) • Water (and other fluids) within rocks and minerals move during metamorphism which accelerates solid-state chemical reactions and changes rock composition • 5. Time  Millions of years!

  7. Evidence of Metamorphism Shale 1. Bent (deformed) layers Gneiss

  8. Evidence of Metamorphism Differential pressure “squashes” rock and included features 2. Flattened Pebbles Conglomerate Metaconglomerate

  9. Evidence of Metamorphism 3. Crystalline Texture Minerals tightly interlocking due to recrystallization under pressure Quartz Sandstone Quartzite

  10. Evidence of Metamorphism 4. New mineral configurations E.g., Shale: Clay minerals (some quartz)  Metamorphism (Mid-grade) Forms Schist: Mica, Feldspar and other silicate minerals 

  11. Categories of Metamorphic Rocks • Foliated - Metamorphic rocks that exhibit parallel alignments of minerals. In these rocks, the minerals all line up perpendicular to the exerted pressure. • Non-foliated - Metamorphic rocks composed of minerals that are not elongated or flat, do not exhibit parallel alignments. • Grade: Low grade means relatively low amounts of heat and pressure during the metamorphic process.

  12. Types of Metamorphic Rocks 25. Name:Slate Grade:Low Category: Foliated Parent Rock:Shale Unique Characteristics: • Homogenous Rock

  13. Types of Metamorphic Rocks 26. Name:Mica Schist Grade:Medium Category: Foliated Parent Rock:Clay and Mudstone Unique Characteristics: • Flaky texture • Contains elongated minerals

  14. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  15. Types of Metamorphic Rocks 28. Name:Quartzite Grade:High Category: Non-foliated Parent Rock:Quartz Sandstone Unique Characteristics: • Light in colour • Very hard

  16. Types of Metamorphic Rocks 29. Name:Amphibolite Grade:Medium Category: Non -Foliated Parent Rock:Basalt Unique Characteristics: • Little or no quartz • Often a salt and pepper colour.

  17. Types of Metamorphic Rocks 30. Name:Marble Grade:Medium Category: Non-Foliated Parent Rock:Limestone and dolostone Unique Characteristics: • Complete re-crystallization of the calcite minerals from the parent rock.

  18. Types of Metamorphic Rocks 31. Name: Banded Gneiss Grade:High Category: Foliated Parent Rock:Igneous and sedimentary rocks Unique Characteristics: • Very common in Ontario.

  19. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  20. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  21. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  22. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  23. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  24. Types of Metamorphic Rocks 27. Name:Garnet Mica Schist Grade:Medium Category: Foliated Parent Rock:Mudstone and Clay Unique Characteristics: • Same as mica schist, but it has garnet in it as well.

  25. Shale: Fine grained Clay (and quartz) Minerals stable under low T&P (atmospheric) Compaction due to accumulation of sediment Water bound in crystalline structure of clay C. Prograde Metamorphism of Shale

  26. Prograde Metamorphism of Shale 1:Low Grade MetamorphismSlate (#25) • Fine grained, homogeneous, • Composed of clay and volcanic ash. • Low grade metamorphic T&P (Water is expelled from crystalline structure of clay) • Minerals (mica) stable under low grade metamorphic conditions

  27. Prograde Metamorphism of Shale 2:Medium-Grade Metamorphism  Phyllite (#34) • Foliated, courser grained • Composed of mica, chlorite, and quartz • Has a gold sheen on the surface of the bands • Medium-grade metamorphic T&P Causes minerals to grow

  28. Prograde Metamorphism of Shale 3: Medium to High-Grade Metamorphism  Mica Schist (#26) • Foliated, course grained, platy or elongated minerals. • Composed of mica and quartz • Can appear flaky. • Medium-grade metamorphic T&P Causes minerals to grow

  29. Prograde Metamorphism of Shale 4:High-Grade Metamorphism  Gneiss(#31 & 33) • Foliated, course grained • Composed of Feldspar, Quartz, Amphibole, Biotite • Looks like schist, but the minerals are made in bands by the high T & P. • Minerals stable under high grade metamorphic conditions appear: feldspar • Gneissic banding bands of dark and light minerals. Fig 7.12

  30. Gneissic granite – separation of dark & light minerals is just beginning Well banded gneiss • Banded Gneiss is made for either sedimentary rock or igneous while granite Gneiss is only made from igneous Augen = quartz pebble resistant to compression Augen Gneiss kink in gneiss

  31. Prograde Metamorphism of Shale 5: Very High-Grade Metamorphism and partial melting Migmatite • Silica rich minerals melt first (quartz and feldspar) • Forming silicic magma • Injected into fractures resulting in silicic veins if intrusive igneous rock Fig 7.12

  32. Metamorphic Rocks of other Parent Rocks • Quartz Sandstone  Quartzite (#28) • It is a hard, non-foliated rock made from sand stone. • Created by high P & T due to tectonic pressure. • It is light in colour and appears sugary.

  33. Metamorphic Rocks of other Parent Rocks • Limestone  Marble (#30) • Non-foliated hard rock. • Created by a complete re-crystalization of the minerals found in the parent limestone or dolomite. • The different colours are cause by impurities.

  34. Metamorphic Rocks of other Parent Rocks • Basalt  Amphibole Schist (#29) • Consists of a mineral called amphibole. Does not have any quartz. • Weakly foliated.

  35. Peridotite - Soap Stone (#35) • Rich in a mineral called talc (magnesium) • Produced where the plates are subducted • Used for carving sculptures.

  36. Serpentinite (#36) • These rocks are formed by process involving the hydration and metamorphic transformation of peridoite from the Earth’s mantle. • Its green colors, waxy luster, often associated asbestos and common slicken-sided surfaces are clues to its identity.

  37. Conglomerate METACONGLOMERATE – non-foliated • It is metamorphosed conglomerate. • It retains its pebbly appearance, but while a sedimentary conglomerate will break around the pebbles, a metaconglomerate will break through the pebbles. • If temperatures are high enough in the presence of pressure, the pebbles may become squished or flattened and will be elongated parallel to each other (becomesfoliated).

  38. Prograde Metamorphism in Mountain Belts Regional Metamorphism

  39. Eastern Zion National Park

  40. Checkerboard Butte Zion National Park

  41. Vishnu Schist and Pink Granite

  42. Homework • P. 139 #1-6