VII. Metamorphic Rocks A.Evidence of metamorphism B.The ingredients of metamorphism C.Prograde metamorphism of shale D.Classification of Metamorphic Rocks E.Metamorphism and Plate Tectonics

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

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)

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 Shale Gneiss

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

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

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 

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

B. Ingredients of Metamorphism 2. Increased Temperature (geothermal gradients) Minerals stable at lower temperatures converted to minerals stable at higher temperatures Solid state chemical reactions are accelerated Temp. (ºC) ABC See Kehew, Fig. 5-1, 5-2 A C B

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

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

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!

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

Prograde Metamorphism of Shale 1: Low Grade Metamorphism  Slate Fine grained Mica, (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 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 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 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 Fig 7.12

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

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

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

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

Prograde Metamorphism in Mountain Belts Regional Metamorphism

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

Reading the Grand Canyon

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

The Grand Staircase Fig. 8.16

Eastern Zion National Park

Checkerboard Butte Zion National Park

Vishnu Schist and Pink Granite