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VII. Metamorphic Rocks

VII. Metamorphic Rocks. Evidence of metamorphism The ingredients of metamorphism Prograde metamorphism of shale Classification of Metamorphic Rocks Metamorphism and Plate Tectonics. Geological Materials Transformation Processes. The Rock Cycle. Rock Metamorphism

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VII. Metamorphic Rocks

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

  2. Geological Materials Transformation Processes The Rock Cycle • Rock Metamorphism (Increased T & P) • Meta- morphic rock Partial Melting • Magma

  3. MetamorphismMetamorphic Rocks Definition: • Re-crystallization of minerals • While still solid • Into minerals that are stable at different temperatures and • Different pressures (Usually progressively higher temperatures and pressures)

  4. A. Evidence of Metamorphism Shale E.g., Sedimentary Rocks • Made of minerals derived from weathering of a parent rock • Stable at atmospheric temperatures and pressures (low T & P) • Originally horizontal, continuous and uniform layers • 1. Bent (deformed) layers Gneiss

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

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

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

  8. B. Recipe of Metamorphism • 1. Parent Rock • Even though minerals will change • Most elements are provided by parent rock • Except water and some dissolved ions Shale Schist

  9. B. Ingredients of Metamorphism 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 See Kehew, Fig. 5-1, 5-2

  10. 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

  11. Compressive Stress Shear Stress Cause Foliation Results of Stress See Kehew, Fig. 5-8

  12. Ingredients of Metamorphism • 4. Addition or removal of fluids (and elements) • Water (and other fluids) within rocks and minerals • Moving during metamorphism • Accelerates solid-state chemical reactions and • May change rock composition • 5. Time  Millions of years!

  13. C. Prograde Metamorphism of Shale (and the classification of metamorphic rocks) Shale: Fine grained Clay (and quartz) • Minerals stable under low T&P (atmospheric) • Compaction due to accumulation of sediment • Fissility along laminations • Water bound in crystalline structure of clay

  14. 1: Low Grade MetamorphismSlate Fine grainedMica, (chlorite and Quartz) Low grade metamorphic T&P (Water is expelled from crystalline structure of clay) Minerals stable under low grade metamorphic conditions Slaty Cleavage due to realignment of platy minerals Prograde Metamorphism of Shale

  15. 2: Medium-Grade Metamorphism  Phillite Courser grained Mica and quartz Medium-grade metamorphic T&P Causes minerals to grow Slaty cleavage becomes rippled and rock has a sheen Prograde Metamorphism of Shale

  16. 3: Medium to High-Grade Metamorphism  Schist Course grained Mica and Quartz Medium-grade metamorphic T&P Causes minerals to grow Minerals stable under medium grade metamorphic conditions appear: Garnet, amphibole and biotite Schistosity due to alignment of platy and needle likeminerals Prograde Metamorphism of Shale

  17. 4: High-Grade Metamorphism  Gneiss Course grained Feldspar, Quartz, Amphibole, Biotite High-grade metamorphic T&P Causes minerals to separate into bands Minerals stable under high grade metamorphic conditions appear: feldspar Gneissic banding bands of dark and light minerals Prograde Metamorphism of Shale Fig 7.12

  18. 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 Prograde Metamorphism of Shale Fig 7.12

  19. Metamorphic Rocks of other Parent Rocks • Limestone  Marble • Bioclastic calcite  Crystalline calcite Nonfoliated

  20. Metamorphic Rocks of other Parent Rocks • Quartz Sandstone  Quartzite • Granular quartz  Crystalline quartz Nonfoliated

  21. Metamorphic Rocks of other Parent Rocks • Basalt  Amphibole Schist • Granite  Gneiss • Uniform texture  Foliation (schistosity and gneissic banding)

  22. Prograde Metamorphism in Mountain Belts Regional Metamorphism

  23. Northeastern North America Metamorphic Grade High Low Kehew, Fig. 5-5 Northwestern Africa

  24. Reading the Grand Canyon

  25. The Grand Canyon Fig. 8.16 The Grand Staircase 5. Coconino Sandstone 4. Redwall Limestone Sedimentary Rocks Intrusive Igneous Metamorphic 3. Bright Angel Shale 2. Grand Canyon Pink Granite 1. Vishnu Schist (and gneiss)

  26. The Grand Staircase Fig. 8.16

  27. Eastern Zion National Park

  28. Checkerboard Butte Zion National Park

  29. Vishnu Schist and Pink Granite

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