Metamorphism, metamorphic rocks, and hydrothermal rocks (2)

Foliated Textures – Mineral Banding Gneiss... Foliated Textures – Mineral Banding Gneiss... Foliated Textures – Mineral Banding Gneiss... Barrovian MetamorphismMetamorphoses Into Large c

Rock Classification

Metamorphic Rock

Textures

Sedimentary layers have just

Slaty Cleavage

http://www.accd.edu/sac/EARTHSCI/1301.090/Lecture%202.htm

Foliated Textures Slaty Cleavage

http://www.creativeroofsystems.com/services.htm http://www.restorationtrades.com/articles/roofslatetile.shtml

Slaty Cleavage and its Practical Applications

http://www.bingleystone.com/stoneslate/indian-p1.htm

Slaty Cleavage and its Practical Applications

develops into

Which then

Develops into

Foliated Textures

Schistosity and Mineral Banding

A foliation is any planar fabric in a metamorphic

rock In this case, the foliation is defined by aligned

sheets of muscovite sandwiched between quartz

grains

Foliated Textures - Schistosity

Foliated Textures - Schistosity

Schist

Foliated Textures – Mineral Banding

Gneiss

Foliated Textures – Mineral Banding

Gneiss

Foliated Textures – Mineral Banding

Gneiss

Foliated Textures – Mineral Banding

Gneiss

Foliated Textures – Mineral Banding

Gneiss

Textural Responses to Changes in Metamorphic Temperature-Pressure

Granular Textures

Quartz sandstone – pure silica

Limestone – pure CaCO 3

Metamorphic Rock Classification and Formation

Metamorphic Rock Classification and Formation

The trouble with metamorphism is

Any kind of rock, igneous,

sedimentary, or metamorphic

Can undergo any kind of

metamorphism

Producing every conceivable

combination and permutation.

Metamorphic Rocks are Very

Complex

Dull “thunk” sound when

struck

Metamorphoses

Into

Small chlorite crystals

Slaty cleavage Rings like a bell when struck

Barrovian Metamorphism

Metamorphoses

Into

Large chlorite crystals Slaty cleavage – coarser

grained foliation Has a definite sheen in reflected light; back to dull

Barrovian Metamorphism

Large chlorite

crystals Slaty cleavage – coarser grained

foliation Has a definite sheen in

reflected light; back to dull

Schistosity; minerals completely intermixed Minerals large enough to be easily identified

Schist

Schist: a type of layering or foliation typical of metamorphic rocks where minerals large enough to be seen by eye show definite orientations

• Greenschist (chlorite dominated)

• Blueschist (glaucophane dominated, plus many other minerals)

• Amphibolite schist (Amphibole dominated)

• Greenschist facies – low

grade

Then there is the issue of rocks and facies

• Amphibolite facies – middle grade

• Granulite facies – high grade

• Greenschist the rock

• Amphibolite the rock

• Granulite the rock

Barrovian Metamorphism

Chlorite Schist

Barrovian Metamorphism

Biotite Schist

Garnet Muscovite Schist

Barrovian Metamorphism

Amphibolite Schist

Barrovian Metamorphism

Measuring Metamorphic Intensity

Metamorphic rocks are important for a variety of

reasons One is that many minerals are formed only

during metamorphism, and many of these are

extremely valuable Many gem minerals are

metamorphic, such as rubies Other metamorphic

minerals are economically important, or important in

manufacturing.

Geologically, metamorphic rocks and minerals are

valuable because they serve as barometers of

temperature and pressure conditions of the times and

places where they formed – always deep in the earth

We are able to unravel the origin and history of not

only these rocks but also the Earth from the study of

metamorphic rocks.

Zones and Facies

We can see some of

these changes in the

phase diagrams to the

right The same

http://www.clan-mackenzie.co.uk/graphics/highlands.jpg

http://www.scotland.de/photos/073landx.jpgScottish Highlands

http://www.kentleton.evesham.net/Photo/03/030612d.htmScottish Highlands

http://www.cast.uark.edu/cast/interact/buchaille_1600x1200.jpgScottish Highlands

http://niovi.aueb.gr/~nts/images/scottish_highlands.jpgScottish Highlands

Measuring Metamorphic Intensity

George Barrow mapped a widespread

series of zones of progressive

metamorphism, as observed in the

Dalradian sequence exposed in Scottish

Highlands, in the late 19th century

Each zone recognized is based on the

first appearance of a group of

distinctive index minerals as the

highest metamorphic grade, along the

thermal axis, was approached

Barrow believed the zones resulted

from the heat from the small granitic

intrusives found in the high grade zones

- Contact Metamorphism

Another geologist, (C.E Tilley)

working on the same rocks in a different

area suggested that the temperature of

each zone was largely determined by

the depth of burial (geothermal

gradient), modified at depth by heat

from the intruded granites. http://www.brocku.ca/earthsciences/people/gfinn/petrology/aberdeen.gif

Zones and Facies

http://www.tulane.edu/~sanelson/eens212/regionalmetamorph.htm

Read Summary at this web site

Metamorphic Zone Minerals

Metamorphic Zone Minerals

CHLORITE

Metamorphic Zone Minerals

BIOTITE

Metamorphic Zone Minerals

GARNET

http://mines.unr.edu/museum/minerals/staurolite.jpg

Metamorphic Zone Minerals

STAUROLITE

This is a schist consisting almost entirely of staurolite and muscovite Note that

some of the staurolite crystals have formed the crosses that distinguish

staurolite.

http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Schist/SchistStauroliteCUp.jpg

Barrovian Metamorphism

Staurolite Fairy Cross Stones

Barrovian Metamorphism

Staurolite Fairy Cross Stones

Barrovian Metamorphism

Metamorphic Zone Minerals

KYANITE

This is a garnet-kyanite-quartz schist The large purple garnets look like

candies The kyanite grains are the bluish gray flat grains found here

and there, especially in the top of the photo.

http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Schist/SchistDurhamGarnetKynCUp1.jpg

Barrovian Metamorphism

Metamorphic Zone Minerals

SILLIMANITE

Metamorphic Zone Minerals

SILLIMANITE – THIN SECTION

Barrovian Metamorphism of Mafic Igneous Rocks

Gabbro

Metamorphoses

Into

Greenschist

Barrovian Metamorphism of Mafic Igneous Rocks

Metamorphoses

Into

Amphibolite Greenschist

Barrovian Metamorphism of Mafic Igneous Rocks

Amphibolite

Metamorphoses

Into

Granulite

Barrovian Metamorphism of Mafic Igneous Rocks

Prof Li Jinghai examining boudin of metagabbro (HP mafic

granulite) in tonalitic gneiss Dashigou River, Hengshan

Complex, northern China

Retrograded HP mafic granulite (gabbroic dyke) showing garnet rimmed by plagioclase Dashigou River, Hengshan Complex, northern China.

http://www.staff.uni-mainz.de/kroener/China1.htm

Ancient Volcanic Island Arcs

Preserved in the Piedmont of Virginia

The Barrovian Facies Series occurs in the southern Appalachians, extending from

Central Virginia to Alabama.  Interpretation of the relationship between deformation

and metamorphism is complicated by the fact the region has experienced at least

three mountain building events, and thrust faults cut the area

Barrovian Facies Series of the Southern Appalachians

Quartzite Quartzite Quartzite Quartzite

Marble Marble Marble Marble

Slate/

Phyllite Schist Gneiss Hornfels

Gneiss Gneiss Gneiss Pegmatite

Green-schist Amphibo- lite Granulite

basalt Soapstone Serpentine

Meta-Sandy

phyllite Schist Gneiss

Sandy hornfels

Sandy

phyllite Schist Gneiss

Sandy hornfels

Eclogite

Barrovian Gneiss NA [Biotite] Greenschist Barrovian Marble Greenschist Barrovian Greenschist NA Greenschist Contact Hornfels NA NA

Barrovian Graphite Any

Contact Hornfels None

Barrovian Schist Garnet Amphibolite

[Chlorite]

NA

Barrovian Gneiss Kyanite/ Sillimanite Granulite

The Rock Cycle

All rocks can be

The Earth as a Complex Evolutionary System

Evolutionary Rock Cycles

Evolutionary Rock Cycles

Rising Decompressing Mafic/ultramafic Parent

Parent Rock

(Ultramafic/Mafic)

Mafic OceanBasalt/gabbro

Ultra-mafic Fractionation residue

Early Fractional Melting

IntermediateDiorite, plagiogranite

And, Sedimentary Rocks Evolve

And, Metamorphic Rocks Evolve

Earth About Four Billion Years

Ago Oceans are established and Volcanic Islands are springing

up.

~ 4.05 Ga Volcanic eruptions on the early Earth, showing the dark

smoggy atmosphere and tremendous lightening displays that

accompanied it The atmosphere would have been filled with thick,

choking, poisonous gasses Land areas were small, while tides and

ocean currents strong.

Evolutionary Rock Cycles

Fiji New Zealand

Innumerable Volcanic Arcs and Collisions Among These Arcs Over Two Billion Years Build

the Cores Of Modern

Continents

Small volcanoes and microcontinents, moving

across the earth are bound to collide, and stick

together to form even larger continents It was this process that built the large continents we see

today

All explained through tectonic

theory Our next subject.