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Metamorphic Rocks

GEOL 101 Lecture 9

2006

JS Kite WVU

What is story behind this rock?

Test 1 Results Posted this Morning athttp://www.geo.wvu.edu/~kite/teaching.html

Test 061111 & 061122: add 9Test 061133 & 061144: add 7

A = >88B = 75 to 87C= 62 to 74D = 50 to 62

F < 50Class Average = 66.83

Diagenesis:

• All Post-Depositional Physical and Chemical Changes in Sediments and Sedimentary Rocks

• Up to 150OC & 1 kb Pressure

Metamorphism:• Mineralogical & Structural Adjustment to Physical & Chemical Conditions

• Over 150oC & 1 Kb Pressure

Agents of Metamorphism

• Pressure• Temperature• Chemically Active Fluids

(Ion-Rich Water or Gasses)

Types of Metamorphism• Regional Metamorphism

♠Greenschist Metamorphism– High Temperature, High Pressure

♣ Blueschist Metamorphism– Low Temperature, High Pressure

• Contact Metamorphism– High Temperature, Low Pressure

• Shock Metamorphism – Very High Instantaneous Pressure

Where Different Types of Metamorphism Occur

Contact: High Temp., Low Pressure

Regional (= Green Schist): High Heat + High Pressure

1 kb 1 kb

Where Different Types of Metamorphism Occur (See Fig. 7.15, Box 7.3 in Plummer et al., 10th ed.)

Green-schistBlue-schist

Contact

Contact MetamorphismChilled Zones and Baked Zones

Hydrothermal Alteration –Source of Ores (Silver, Gold, Lead, Zinc, Tin, etc.)

Metamorphic Fabric

• Granular• Foliation• Lineated

Granular FabricQuartzite

Stress: Force Applied (to a Rock)

Strain: Rock’s Response to Stress

Strain Ellipse

Regional Metamorphism

Granite - Igneous

Uniform Stress

Gneiss - Metamorphic

DifferentialStress

Foliated Fabric

Fig 7.5 in Plummer et al.10th ed., 2005

Foliated Fabric

Foliatio

n Plane

Foliatio

n Plane

Strain: Stretch-Pebble “Conglomerate”

Strain

Stress

Lineated Fabric

Sorry, No Pictures!

Sequences of Regional Metamorphic Rocks**

Shale Granite Sandstone Limestone Slate Gneiss Quartzite Marble Phyllite Gneiss Quartzite Marble Schist Gneiss Quartzite Marble Gneiss Gneiss Quartzite Marble Migmatite Migmatite Migmatite Migmatite Granite Granite Granite Granite Magma Magma Magma Magma

Original Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Melting

** Leave Room For This TableLeave Room For This Table

4 Slate slides not posted pending permission

• To Explore Slate Quarry Photographs, See http://www.slatevalleymuseum.org

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate

Sed Rock

MetamorphicRock

150oC &/or 1 kb

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate’s color varies

Sed Rock

MetamorphicRock

150oC &/or 1 kb

Slate Quarry in Action

Slate in Storage

Jim Covino'sproduction

http://www.slatevalleymuseum.org/images/chips.jpg

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite (note “sheen”)

Sed Rx

Incr

easi

ngM

etam

orph

ism

Picture for 2001?

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite Schist .

Sed Rx

Incr

easi

ngM

etam

orph

ism

Schist in Thin Section

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite Schist Gneiss .

Sed Rx

Incr

easi

ngM

etam

orph

ism

Gneiss in thin section

Gneiss (sounds nice)

Gneiss OutcropGSNL image

Gneiss

Schist

Slate Phyllite

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite Schist Gneiss Migmatite .

Sed Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Migmatite: Metamorphic Rock that Contains Partially Melted Zones of Igneous Rock

Transitional between Transitional between Metamorphic & IgneousMetamorphic & Igneous

GSNL image

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite Schist Gneiss Migmatite Granite .

Sed Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Granite with Schist Xenolith

GSNL imageGSNL image

Regional Metamorphism of Clay-Rich Sedimentary Rocks

Shale Slate Phyllite Schist Gneiss Migmatite Granite Magma .

Sed Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Melting

Sequences of Regional Metamorphic Rocks

Shale Granite Slate Gneiss Phyllite Gneiss Schist Gneiss Gneiss Gneiss Migmatite Migmatite Granite Granite Magma Magma .

Orig. Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Melting

Sequences of Metamorphic Rocks

Shale Granite Sandstone Slate Gneiss Quartzite Phyllite Gneiss Quartzite Schist Gneiss Quartzite Gneiss Gneiss Quartzite Migmatite Migmatite Migmatite Granite Granite Granite Magma Magma Magma .

Orig. Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Melting

Quartzite in Thin SectionHexagonal Quartz xls

Sequences of Metamorphic Rocks

Shale Granite Sandstone Limestone Slate Gneiss Quartzite Marble Phyllite Gneiss Quartzite Marble Schist Gneiss Quartzite Marble Gneiss Gneiss Quartzite Marble Migmatite Migmatite Migmatite Migmatite Granite Granite Granite Granite Magma Magma Magma Magma .

Orig Rx

Incr

easi

ngM

etam

orph

ism

Partial Melting

Melting

Marble: e.g. Engineering Marble: e.g. Engineering Science Bldg. FoyerScience Bldg. Foyer

ThinSection

Review of Coal Genesis• Plant Fragments • Peat • Lignite• Bituminous Coal• Anthracite Coal

Dia

gene

sis

150oC &/or 1 kbMetamorphism .

Metamorphic Rx from Mafic Igneous Rx

• Greenstone (= Greenschist)• Amphibolite• Serpentinite• Soapstone (Talc + Asbestos) .

Amphibolite

Metamorphic Rx from Mafic Igneous Rx

Index Minerals & Metamorphic Grade for Clay-Rich Rocks

Clays Chlorite Biotite Garnet Staurolite Kyanite Sillimanite

400OC

700OC High Grade

Low Grade

Diagenetic Minerals 150OC

Intermediate Grade

Geologic Map

Aureoles

Name of Rock and Grade

• Comes From HIGHEST Index Mineral Present

• e.g. Staurolite Schist May Have Garnet & Biotite in It .

Isograds: • Lines Separating

Metamorphic Zones

Metamorphic Facies (See Box 7.3, p. 171)

Diagenesis Contact Metamorphism

Regional Metamorphism

PT

Retrograde Metamorphism

• Higher Grade Index Minerals may Break Down to Form Lower Grade Index Minerals

• Requires Chemically Active Fluids &• Long Time at New Temperature &

Pressure .

Porphyroblasts

• Large xls in met. rx• Remember Porphyry (ig. rx)?• Porphyroblasts = Last

Formed Xls .

GSNL image

Staurlolite Porphyroblasts

GSNL image

Augen: Snow-Ball Garnets

GSNL image

Cataclastic Rocks: Mylonite,Friction Breccia (shown below)

GSNL image

Metamorphic Rocks, Continued -Contact Metamorphism

Geology 101 Section 002 Quiz #3 (Due in class (7 oops) 9 February 2006)

• 1. What are minimum temperatures and pressures required for metamorphism of rock?

2. Fill out the following table.

??Dolomite (Same as One of the Above)

Hornfels*Mafic Igneous Rx

Anthracite*Bituminous Coal

Marble*Limestone

Quartzite*Sandstone

Granite: unless heat = extreme

*Granite

Hornfels* * * *Shale

Metam. Rock under Contact Metamorphism

Metamorphic Rock under Regional MetamorphismOriginal Rock

3. Explain the geological history represented by an outcrop of basalt that is intruded by a dike of rhyolite porphyry. The 5-10 cm of rock that was basalt along the dike is now hornfels.

Which rock was there first? Which was there second? What caused the hornfels?