Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of...

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Metamorphism and Metamorphic Rocks Chapter 7

Transcript of Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of...

Page 1: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphism and Metamorphic RocksChapter 7

Page 2: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

MetamorphismMetamorphism

… … is the transformation of rock by is the transformation of rock by temperature and pressuretemperature and pressure

Metamorphic rocks are produced by Metamorphic rocks are produced by transformation of:transformation of:

Sedimentary and Igneous rocks, and by Sedimentary and Igneous rocks, and by the further alteration of other the further alteration of other metamorphic rocksmetamorphic rocks

Page 3: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

0 kmSedimentaryrock

Metamorphicrock

Igneousrock

50 km

10 km

~200ºC

~800ºC

Incr

easi

ng d

epth

and

tem

pera

ture

Melting

Metamorphism

Sedimentaryrock

Sediment

Metamor-phism occurs between about 10 and 50 km of depth

The rocks don’t melt

Page 4: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

NorthCascades

CanadianShield

RockyMountains

Grand Canyon

AppalachianMountains

BlackHills

LlanoUplift

Originally buried deep,metamorphic rocks are seen when erosionremoves covering rocks, and in the coresof mountains

Glaciers exposed the

Best US exposures in New England and the South

Page 5: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

MetamorphismMetamorphism

Metamorphism progresses from low to Metamorphism progresses from low to high gradeshigh grades

Rocks remain solid during metamorphismRocks remain solid during metamorphism

Metamorphism occurs above 50km melting Metamorphism occurs above 50km melting depth for felsic mineralsdepth for felsic minerals

Page 6: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

What causes metamorphism?What causes metamorphism?

1. Heat1. Heat Most important agent Most important agent Heat drives recrystallization - creates new, Heat drives recrystallization - creates new,

stable mineralsstable minerals Increasing Heat with DepthIncreasing Heat with Depth

Page 7: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Temperature Increase with Depth

“Geothermal Gradient” due to:

Radioactive Isotopes

Intruding Magma

Friction Between Moving Bodies of Rock

Page 8: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

What causes metamorphism?

2. Pressure (stress)Increases with depthPressure can be applied equally in all directions or differentiallyAll Directions = “Confining Pressure”also called “lithostatic pressure”

Differential = “Directed Pressure”

Page 9: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Origin of pressure in metamorphism

(due to burial)

(Convergent Margin)

Confining pressure aka “lithostatic”

Page 10: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Confining Pressure

Page 11: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Directed Pressure

Page 12: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Directed Pressure causes rocks to become folded, and minerals to reorient perpendicular to the stress: “foliation”

Source: Kenneth Murray/Photo Researchers Inc.

Page 13: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Foliation

Minerals Recrystallize Perpendicular to the Directed Pressure

If the minerals are flat, such as sheet-like Micas, their parallel orientation gives a layered look; layering unrelated to the original bedding in the parent rock.

Page 14: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Main factors affecting Main factors affecting metamorphismmetamorphism

3. Parent rock3. Parent rock Metamorphic rocks typically have the Metamorphic rocks typically have the

same chemical composition as the rock same chemical composition as the rock they were formed from.they were formed from.

Different minerals, but made of the same Different minerals, but made of the same atoms.atoms.

Page 15: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphic SettingsMetamorphic Settings Three types of metamorphic settings:Three types of metamorphic settings:

ContactContact metamorphism – due heat from adjacent rocks metamorphism – due heat from adjacent rocks HydrothermalHydrothermal metamorphism – chemical alterations from metamorphism – chemical alterations from

hot, ion-rich waterhot, ion-rich water RegionalRegional metamorphism -- Occurs in the cores of metamorphism -- Occurs in the cores of

mountain belts and subduction zones (Converging mountain belts and subduction zones (Converging Margins) . Makes great volumes of metamorphic rock. Margins) . Makes great volumes of metamorphic rock. Includes:Includes:

– BurialBurial Metamorphism – e.g. Burial of sediments Metamorphism – e.g. Burial of sediments deeper than 10 km – non-foliateddeeper than 10 km – non-foliated

– DynamothermalDynamothermal Metamorphism – Directed pressure Metamorphism – Directed pressure in Plate Tectonic Processes - foliatedin Plate Tectonic Processes - foliated

Page 16: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

1. Contact Metamorphism

Baking due to nearby Magma

Effect strongest in rocks in immediate contact

Page 17: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Contact metamorphismProduced mostly by local heat source

Page 18: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Contact MetamorphismMetamorphicAureole

Page 19: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

2. Hydrothermal Metamorphism

Due circulation of water near Magma

Important at mid-ocean ridge

Page 20: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Hydrothermal Metamorphism

Page 21: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

3. Regional Metamorhism3. Regional Metamorhism

Most Most DynamothermalDynamothermal metamorphism metamorphism occurs along convergent plate boundariesoccurs along convergent plate boundaries

Example 1: Continent-Continent CollisionsExample 1: Continent-Continent CollisionsCompressional stresses deforms plate edgeCompressional stresses deforms plate edgeContinents CollideContinents CollideMajor Folded Mountain Belts: Alps, Major Folded Mountain Belts: Alps,

Himalayas, and Appalachian Mts.Himalayas, and Appalachian Mts.

Page 22: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Dynamothermal Metamorphism, Before collision

Sediments are “unconsolidated”. They will fold if pushed.

Page 23: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Dynamothermal Metamorphism, After continental collision

Felsic continental materials and sediments are buoyant, they have low densityThey float, cannot be subducted, so they get squashed.

Page 24: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

2. Regional Metamorphism 2. Regional Metamorphism (continued)(continued)

Most Most Dynamothermal Dynamothermal metamorphism occurs along convergent metamorphism occurs along convergent plate boundariesplate boundaries

Example 2: In Subduction ZonesExample 2: In Subduction Zones

Page 25: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphism in a Subduction Zone

Page 26: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphism and plate tectonicsMetamorphism and plate tectonics

Metamorphism at subduction zonesMetamorphism at subduction zones Cores of subduction zones contain linear belts ofCores of subduction zones contain linear belts of

metamorphic rocksmetamorphic rocks High-P, low-T zones near trenchHigh-P, low-T zones near trench High-T, low-P zones in regions near igneous High-T, low-P zones in regions near igneous

activity within shallow Lithosphere (Crust)activity within shallow Lithosphere (Crust) High P, high-T zones in regions near igneous High P, high-T zones in regions near igneous

activity deeper in Lithosphere (Uppermost activity deeper in Lithosphere (Uppermost Mantle)Mantle)

Page 27: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Oceanic sediments

Basalt

High-temperature/low-pressuremetamorphism

Low-temperature/high-pressuremetamorphism

CONTINENTALCRUST

High-temperature/high-pressuremetamorphism

Page 28: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphic Grade and Metamorphic Grade and Index MineralsIndex Minerals

Certain minerals, called Certain minerals, called index index mineralsminerals, are good indicators of , are good indicators of the metamorphic conditions in which the metamorphic conditions in which they formthey form

Page 29: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Index Minerals in metamorphic rocks

Note Quartz and Feldspar are not index minerals: Why?

Note Temperature gradient

220oC

580oC

460oC 690oC

Page 30: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Here is an internally heated pressure vessel at the AMNH

With these you can study, for example:

1. the temperature and pressure conditions at which polymorphs change from one form to another. (next slide)

2. the reactions of minerals with fluids (for example salty or alkaline water) at high temperatures and pressures.

3. the conditions necessary to change one assemblage of minerals to another

http://research.amnh.org/earthplan/research/Equipment/Petrology

Page 31: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Any Useful Thermometers and Pressure Gauges?

Polymorphs of Al2SiO5

Kyanite

Sillimanite

Andalusite

Page 32: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

7_21CANADA

NEW YORK

CANADA

U.S.A.

Albany

Boston

Scranton LongIsland

Binghamton

ATLANTICOCEAN

Unmetamorphosed

Chlorite/muscovite zone

Biotite zone

Garnet zone

Staurolite zoneSillimanite zoneHigh grade

Mediumgrade

Lowgrade

Augusta

PENNSYLVANIA

NEWHAMPSHIRE

MAINE

MASSACHUSETTS

Concord

Montpelier

VERMONT

CONNECTICUT

NEWJERSEY

R.I.

ProvidenceHartford

Newark

Increasing pressure and temperature

DIAGENESIS LOW GRADEChlorite and muscoviteBiotite

GarnetStaurolite

Sillimanite

INTERMEDIATE GRADE HIGH GRADE MELTING

New EnglandDynamothermalMetamorphism

r i f t

va lley

Page 33: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphic EnvironmentsMetamorphic grade or Facies

A group of minerals that form in a particular P-T environment

Can be used to deduce T-P conditions of formation

Page 34: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphic Environments in Subduction Zones

We can look at minerals in Metamorphic Rocks and determine where they formed.

Water facilitates metamorphic reactions by allowing movement of atoms and ions

Page 35: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Greenschist Hand Sample

Greenschist Thin SectionChl-Ep

Page 36: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

MicaSchist

Page 37: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Blueschist glaucph Amphibolite

Page 38: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks

Nonfoliated rocksNonfoliated rocks QuartziteQuartzite

– Formed from a parent rock of quartz-rich Formed from a parent rock of quartz-rich sandstonesandstone

– Quartz grains are fused togetherQuartz grains are fused together

– Forms in intermediate T, P conditionsForms in intermediate T, P conditions

Page 39: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Sample ofquartzite

Thin sectionof quartzite

Field Geologists are grateful for quartzites. They don’t foliate, so you can see the folds. Mudrocks foliate; much harder to map.

Page 40: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Flattening of quartz grains in quartzite

Page 41: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

7_18

Fracture

Fracture

Sandstone

Quartzite

Page 42: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks Nonfoliated rocks (cont.)Nonfoliated rocks (cont.)

MarbleMarble– Coarse, crystallineCoarse, crystalline

– Parent rock usually limestoneParent rock usually limestone

– Composed of calcite crystalsComposed of calcite crystals

– Fabric can be random or orientedFabric can be random or oriented

Page 43: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Marble (nonfoliated)

Page 44: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks Foliated rocksFoliated rocks

– Type formed depends on metamorphic gradeType formed depends on metamorphic grade

– Grade depends on depthGrade depends on depth

Page 45: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Change in metamorphic grade with depth

Increasing Directed Pressure and increasing Temps

Mudstones are sediments, can be squashed by burial and/or in continent-continent collisions

Page 46: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks Foliated rocksFoliated rocks

SlateSlate–Very fine-grainedVery fine-grained

–Excellent rock cleavage, often perp. Excellent rock cleavage, often perp. to originalto original

–Made by low-grade metamorphism Made by low-grade metamorphism of shaleof shale

Page 47: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Example of slate

Page 48: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks

Foliated rocksFoliated rocksPhyllitePhyllite

– Grade of metamorphism between slate and Grade of metamorphism between slate and schistschist

– Made of small platy mineralsMade of small platy minerals– Glossy sheen with rock cleavageGlossy sheen with rock cleavage– Composed mainly of muscovite and/or Composed mainly of muscovite and/or

chloritechlorite

Page 49: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Phyllite (l) and Slate (r)

lack visible mineral grains

Page 50: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks

Foliated rocksFoliated rocks

SchistSchist–Medium- to coarse-grained Medium- to coarse-grained

–Comprised of platy minerals (micas)Comprised of platy minerals (micas)

–The term The term schist schist describes the texturedescribes the texture

–To indicate composition, mineral names To indicate composition, mineral names are used (such as mica schist)are used (such as mica schist)

Page 51: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

A mica garnet schist

Page 52: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Common metamorphic rocksCommon metamorphic rocks Foliated rocksFoliated rocks

GneissGneiss–Medium- to coarse-grainedMedium- to coarse-grained

–Banded appearanceBanded appearance

–High-grade metamorphismHigh-grade metamorphism

–Composed of light-colored feldspar Composed of light-colored feldspar layers with bands of dark mafic layers with bands of dark mafic mineralsminerals

Page 53: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Gneiss displays bands of light and dark minerals

Page 54: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

What are metamorphic What are metamorphic textures?textures?

TextureTexture refers to the size, shape, and refers to the size, shape, and arrangement of mineral grains within a arrangement of mineral grains within a rockrock

FoliationFoliation – planar arrangement of – planar arrangement of mineral grains within a rockmineral grains within a rock

Page 55: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Outcrop of foliated gneiss

Page 56: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Metamorphic texturesMetamorphic textures

FoliationFoliation

Foliation can form in various ways:Foliation can form in various ways:

–Rotation of platy or elongated mineralsRotation of platy or elongated minerals

–Recrystallization of minerals in a Recrystallization of minerals in a preferred orientationpreferred orientation

–Changing the shape of equidimensional Changing the shape of equidimensional grains into elongated and aligned shapesgrains into elongated and aligned shapes

Page 57: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Flattened Pebble Conglomerate = flattening

Page 58: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Development of foliation due to directed pressure

Page 59: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

Migmatites- When Partial Melting StartsHeat the rock, when the minerals with the lowest melting points (Qtz, Feldspar) at that pressure melt then recrystallize, we get separate bands of Metamorphic and Igneous rock

Page 60: Metamorphism and Metamorphic Rocks Chapter 7. Metamorphism Metamorphism … is the transformation of rock by temperature and pressure … is the transformation.

End of Chapter 7