1 / 36

IX. Metamorphic Rocks

IX. Metamorphic Rocks. Evidence of metamorphism The recipe for metamorphism Prograde metamorphism of shale Classification of Metamorphic Rocks Metamorphism and Plate Tectonics. Geological Materials Transformation Processes. The Rock Cycle. Rock Metamorphism (Increased T & P)

saman
Télécharger la présentation

IX. Metamorphic Rocks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. IX. Metamorphic Rocks Evidence of metamorphism The recipe for 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 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

  5. Fig. 8-1, p. 168

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

  7. Evidence of Metamorphism • 3. Crystalline Texture Minerals tightly interlocking due to recrystallization under pressure

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

  9. 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

  10. B. Ingredients of Metamorphism Temp. (ºC) 0 500 1000 • 2. Increased Temperature (high geothermal gradients) • Minerals stable at lower temperatures converted to • minerals stable at higher temperatures • Solid state chemical reactions are accelerated A B C

  11. Ingredients of Metamorphism • 3. Increased Pressure (and stresses) • Increased Lithostatic Pressure as rocks are buried • Differential Pressure at convergent plate boundary or

  12. Fig. 8-3, p. 169

  13. Differential Pressure Parallel alignment of platy minerals (e.g., micas) and needle-like minerals (e.g., amphiboles) Forms Foliation Results of Stress (Pressure)

  14. 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!

  15. 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

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

  17. 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

  18. 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

  19. 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

  20. 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

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

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

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

  24. Where does Prograde Metamorphism occur? Temp. (ºC) 0 600 1200 • Where temperatures and pressures are progressively increased: Subduction zones and Mountain belts • Regional Metomorphism at • Convergent plate boundaries A B C

  25. Prograde Metamorphism in Mountain Belts

  26. Northeastern North America Metamorphic Grade High Low Northwestern Africa

  27. Review for Exam For each rock type discussed know: • Grain size (rounding and sorting if sedimentary) • Texture (clastic or crystalline) • Other characteristics • Various types of metamorphic foliation • Various sedimentary structures • Environment of formation • History of formation Rock Classification

  28. Reading the Grand Canyon

  29. 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)

  30. The Grand Staircase Fig. 8.16

  31. Eastern Zion National Park

  32. Checkerboard Butte Zion National Park

  33. Vishnu Schist and Pink Granite

More Related