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

Metaphoric Rocks These are ricks that have changed (meta) their form

(morphic). Under the influence of heat, pressure and fluids, pre-

existing rocks are modified in form and even in internal atomic structure to produce new rocks stable at the new conditions.

This is done within the solid state, i.e. without melting. Changes that occur include:

increase in grain size, new mineralsfoliation (parallel alignments).

Formation of Metamorphic Rocks 1. Parent Rock

Even though minerals will change most elements are provided by parent rock except water and some dissolved ions

Shale

Schist

2. Increased Temperature (geothermal gradients) Minerals stable at lower temperatures converted to minerals stable

at higher temperatures. Solid state chemical reactions are accelerated

0 600 1200Temp. (ºC)

A B C

A C B

Formation of Metamorphic Rocks

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

Ingredients of Metamorphism

4. Addition or removal of fluids (and elements)

Water (and other fluids) within rocks and minerals move during metamorphism which accelerates solid-state chemical reactions and changes rock composition

5. Time Millions of years!

Evidence of Metamorphism

1. Bent (deformed) layers

Shale

Gneiss

Differential pressure “squashes” rock and included features

2. Flattened Pebbles

Conglomerate

Metaconglomerate

Evidence of Metamorphism

3. Crystalline Texture Minerals tightly interlocking due to recrystallization under pressure

Quartz Sandstone

Quartzite

Evidence of Metamorphism

Evidence of Metamorphism4. New mineral

configurations E.g., Shale: Clay minerals (some quartz)

Metamorphism(Mid-grade)

Forms Schist: Mica, Feldspar and other silicate minerals

Categories of Metamorphic RocksFoliated - Metamorphic rocks that exhibit parallel

alignments of minerals. In these rocks, the minerals all line up perpendicular to the exerted pressure.

Non-foliated - Metamorphic rocks composed of minerals that are not elongated or flat, do not exhibit parallel alignments.

Grade: Low grade means relatively low amounts of heat and pressure during the metamorphic process.

Types of Metamorphic Rocks25. Name: SlateGrade: LowCategory: FoliatedParent Rock: ShaleUnique Characteristics: Homogenous Rock

Types of Metamorphic Rocks26. Name: Mica SchistGrade: MediumCategory: FoliatedParent Rock: Clay and

MudstoneUnique Characteristics: Flaky texture Contains elongated

minerals

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks28. Name: QuartziteGrade: HighCategory: Non-foliatedParent Rock: Quartz

SandstoneUnique Characteristics:

Light in colour Very hard

Types of Metamorphic Rocks29. Name: AmphiboliteGrade: MediumCategory: Non -FoliatedParent Rock: BasaltUnique Characteristics:

Little or no quartz Often a salt and pepper

colour.

Types of Metamorphic Rocks30. Name: MarbleGrade: MediumCategory: Non-FoliatedParent Rock: Limestone

and dolostoneUnique Characteristics: Complete re-

crystallization of the calcite minerals from the parent rock.

Types of Metamorphic Rocks31. Name: Banded GneissGrade: HighCategory: FoliatedParent Rock: Igneous

and sedimentary rocksUnique Characteristics:

Very common in Ontario.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

Types of Metamorphic Rocks27. Name: Garnet Mica

SchistGrade: MediumCategory: FoliatedParent Rock: Mudstone

and ClayUnique Characteristics: Same as mica schist, but

it has garnet in it as well.

C. Prograde Metamorphism of Shale

Shale: Fine grained Clay (and quartz)

Minerals stable under low T&P (atmospheric)

Compaction due to accumulation of sediment

Water bound in crystalline structure of clay

Prograde Metamorphism of Shale

1: Low Grade MetamorphismSlate (#25)

Fine grained, homogeneous,

Composed of clay and volcanic ash.

Low grade metamorphic T&P (Water is expelled from crystalline structure of clay)

Minerals (mica) stable under low grade metamorphic conditions

Prograde Metamorphism of Shale

2: Medium-Grade Metamorphism Phyllite (#34)

Foliated, courser grained

Composed of mica, chlorite, and quartz

Has a gold sheen on the surface of the bands

Medium-grade metamorphic T&P Causes minerals to grow

Prograde Metamorphism of Shale

3: Medium to High-Grade Metamorphism Mica Schist (#26)

Foliated, course grained, platy or elongated minerals.

Composed of mica and quartz

Can appear flaky. Medium-grade metamorphic

T&P Causes minerals to grow

Prograde Metamorphism of Shale

4: High-Grade Metamorphism Gneiss(#31 & 33)

Foliated, course grained Composed of Feldspar,

Quartz, Amphibole, Biotite Looks like schist, but the

minerals are made in bands by the high T & P. Minerals stable under high grade metamorphic conditions appear: feldspar

Gneissic banding bands of dark and light minerals.

Fig 7.12

1. Banded Gneiss is made for either sedimentary rock or igneous while granite Gneiss is only made from igneous

Gneissic granite – separation of dark & light minerals is just beginning

Well banded gneiss

Augen Gneiss

Augen = quartz pebble resistant to compression

kink in gneiss

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

FOLIATED: Rocks have layers or banding

SLATE: Rock breaks into very thin layers Beginning to look polished; Is harder than shale Cannot see crystals Black , gray or red

PHYLLITE: Like slate, but shinier (“phyllitic sheen” — similar to satin)

SCHIST: Very shiny — you can SEE CRYSTALS (usually MICA) Is layered May have crystals (of garnet, tourmaline, etc.) growing with the mica

GNEISS: Crystalline Black & White BANDING (due to segregation of minerals)

Metamorphic Rocks of other Parent Rocks

Quartz Sandstone Quartzite (#28) It is a hard, non-foliated rock

made from sand stone. Created by high P & T due to

tectonic pressure. It is light in colour and

appears sugary.

Metamorphic Rocks of other Parent Rocks

Limestone Marble (#30) Non-foliated hard rock. Created by a complete re-

crystalization of the minerals found in the parent limestone or dolomite.

The different colours are cause by impurities.

Metamorphic Rocks of other Parent Rocks

Basalt Amphibole Schist (#29)

Consists of a mineral called amphibole. Does not have any quartz.

Weakly foliated.

Peridotite - Soap Stone (#35) Rich in a mineral called talc

(magnesium)

Produced where the plates are subducted

Used for carving sculptures.

Serpentinite (#36) These rocks are formed by process

involving the hydration and metamorphic transformation of peridoite from the Earth’s mantle.

Its green colors, waxy luster, often associated asbestos and common slicken-sided surfaces are clues to its identity.

METACONGLOMERATE – non-foliated

It is metamorphosed conglomerate.

It retains its pebbly appearance, but while a sedimentary conglomerate will break around the pebbles, a metaconglomerate will break through the pebbles.

If temperatures are high enough in the presence of pressure, the pebbles may become squished or flattened and will be elongated parallel to each other (becomes foliated).

Conglomerate

CLUES TO METAMORPHIC ROCKS

NON-FOLIATED: Shows NO layers or banding

MARBLE: Sugary looking Will fizz in HCl (acid) Often is multi-colored, may be white Soft — will not scratch glass

QUARTZITE: Very dense MAY look a bit sandy Very hard — will easily scratch glass

METACONGLOMERATE: Looks like sedimentary conglomerate, BUT it is harder (BREAKS THROUGH PEBBLES) and often the pebbles are squished & aligned (it is at this point foliated)

SERPENTINITE: Composed of members of the serpentine family (includes chrysotile asbestos) Generally light greenish gray to greenish black Waxy luster Often exhibit curved and slickensided surfaces

Prograde Metamorphism in Mountain Belts

Regional Metamorphism

Eastern Zion National Park

Checkerboard Butte Zion National Park

Vishnu Schist and Pink Granite

Homework

P. 139 #1-6