types of metamorphism - brock university · types of metamorphism ... in very large belts...

ERSC 3P21 Metamorphic Petrology III 24/08/2011

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ERSC 3P21 - Brock University Greg Finn

Types of Metamorphism• _________________________• _________________________• _________________________• _________________________• _________________________


Regional Metamorphism• Corresponds to changes, _________, in

Temperature & Pressure, due to _____• Commonly associated with _________

events and processes• Regionally metamorphosed rocks occur

in very large belts 10-100's km wide x 100-1000's km long.


Regional Metamorphism• Within each belt will be preserved at least

______________, representing the ________ temperature of metamorphism within the belt.

• Temperatures will __________ towards the thermal axis.

• Associated ________ and/or __________ masses intruded into the terranes generally, but not always near the thermal axis.


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Regional Metamorphism

At point A temperature = 400°C, pressure = 3.5 kbars

From: Marshak 2001


Superior ProvinceSubprovince Types

Bird River

MinnesotaRiver Valley

Winisk

Thompson Belt

N

0 250 Km

Hudson Bay

James Bay

Manito

baOntar

io

CanadaU.S.A.

Southern Province

GrenvilleProvince

Ontario

Quebec

Labrador Trough

Sugluk

CapeSmithBelt

Trans - Hudson Orogen

St. Catharines

Pikwitonei

Sachigo

Berens River

UchiEnglish River

Winnipeg RiverWabigoon

Wawa

Wawa

Quetico

Quetico

Kapu

skas

ing

Pontiac

AbitibiOpatica

Nemiscau R.

AshuanipiBienville

La Grande R.

Opinica R.

Minto

High Grade

Plutonic

Volcanic

Metasedimentary

Modified from Percival 1989


Contact Metamorphism• Recrystallization, production of

metamorphic mineral assemblages, within the ______________ surrounding an intrusive body

• Generally held that P remains _______ and metamorphism results from temperature _________, due to conduction of heat away from intrusive


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ContactMetamorphism

From: Marshak 2001


An example of contact metamorphism on I-25 just north of Las Vegas, New Mexico. The mafic intrusion cooked the sedimentary strata (shale and chalk). The width of the zone of contact metamorphism is about 20 feet. From: http://www-class.unl.edu/geol101i/07_metamorphic.htm

ERSC 3P21 - Brock University Greg Finnhttp://www.gpc.edu/~janderso/images/metafaci.jpg


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Pyro-metamorphism• Recrystallization at high __________ of

xenolith fragments in volcanic rocks or small intrusions

• Melting of the xenolith may occur


Hydrothermal Metamorphism• Recrystallization associated with and

influenced by a hydrothermal solution -_________________

• Rocks that are altered at _______ temperatures and ________ pressures by hydrothermal fluids are hydrothermally metamorphosed.

• This is common in basaltic rocks that generally lack hydrous minerals.


Hydrothermal Metamorphism• Hydrothermal metamorphism results in

alteration to such _______ rich hydrous minerals as talc, chlorite, serpentine, actinolite, tremolite, zeolites, and clay minerals.

• __________________are often formed as a result of hydrothermal metamorphism.


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Cataclastic Metamorphism• Cataclastic metamorphism occurs as a result

of __________________________– eg. when two bodies of rock slide past one

another along a fault zone.• Heat is generated by the ________ of sliding

along such a shear zone, and the rocks tend to be mechanically deformed, being _______ and __________, due to the shearing.

• Cataclastic metamorphism is not very common and is restricted to a ________ zone along which the shearing occurred.


CataclasticMetamorphism

From: Marshak 2001


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Compositional Groups• Loose groupings of metamorphic rocks

based on the original ________ composition– Mudstones ___________– Basic Rocks ___________– Ultramafics ___________– Calcareous ___________– Granites ___________


Pelites• Derived from ________ sediments (mudstones)• Characterized by high _____ and ______ contents,

which result in abundant _______ produced during metamorphism– Muscovite - common in _____ _______ pelites– Biotite - common in ______ _____ pelites

• Pelites often display a well developed ___________, defined by parallel alignment of micas – Mica schists

• Also have minerals rich in _____ in pelites, e.g.,– Kyanite, andalusite, sillimanite - Al2SiO5– Staurolite - Fe2Al9O6(SiO4)4(OH)2– Cordierite - Mg2Al3(AlSi)5O18– Garnet - (Fe,Mg)3Al2(SiO4)3


kyanite muscovite schist biotite schist

garnet biotite schist Garnet muscovite schist


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Pelite

a

gt

st

stmu

mu

bi

bi

q

q

a b

gtstmu

muq

q

q

Plate 4: Sample 88-2 - Pelite (metamorphosed mudstone) the minerals present in this rock are produced as a result of metamorphism, increased Temperature and Pressure. Minerals: garnet (gt), staurolite (st), muscovite (mu), biotite (bi) and quartz (q). (FOV = 13.5mm)


Metabasites• Equivalent to _________ rocks with . 50 wt % SiO2• Basalts are often included in sedimentary piles within

orogenic belts, thus mineral assemblages in metabasites can be _________ with assemblages in associated pelites as both formed under similar P &T.

• Basic rocks rich in MgO, FeO, CaO and Al2O3, metamorphic minerals produced include:– Chlorite, actinolite, epidote, at low temp greenschist– Hornblende, plagioclase in amphibolite– Hornblende, plag & garnet, opx & cpx in granulite


Metabasite

a b

p

cpx

op

cpx

cpxcpx

oppp

pp

p

hbhb

hb hb

Sample 99-3 - Amphibolite (metamorphosed gabbro) under (a) plane light and (b) crossed polars. Minerals present include plagioclase (p), clinopyroxene (cpx) (note the variable colour (pleochroism) of the cpx brown and green), hornblende (hb) and opaques (op). (FOV = 8.5mm)


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Barrovian Metamoprhism• Named for _______

__________, who first mapped these lithologies in the 19th

century• Rocks are the _______

sequence that outcrop in the Scottish Highlands

• The Dalradian sequence consists of Precambrian and early Cambrian _________, overlain by unmetamorphosed Upper Devonian Sandstones.

DalradianMoinianLewisian andTorridonian

0 50Scale, km

N

Aberdeen

Inverness

Highland Boundary Fault

Great G

len F

ault

Moi

ne T

hrus

t

BuchanZones

Area investigatedby Barrow

From: Turner 1968


Barrovian Metamoprhism• Within the Dalradian sequence, Barrow

recognized the existence of unmetamorphosed _____ (______) which subsequently underwent metamorphism.

• Barrow recognized a series of zones of ___________ metamorphism


Barrovian Metamoprhism• Each zone is based on the first appearance

of a distinctive ____________ as the highest metamorphic grade, along the thermal axis, was approached.

• Thermal axis has abundant ________ bodies along its length.

• Index mineral is one which is __________ of that zone - any mineral within the zone may be the index mineral.


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Barrovian MetamoprhismThe following zones were recognized by

Barrow:• Zone of _________________________

– now termed chlorite zone - characterized by first appearance of chlorite

– assemblage - qtz-chlorite-muscovite-albite• ____________ Zone

– marked by the first appearance of red-brown biotite from muscovite & chlorite

• ____________ Zone– assemblage - qtz-musc-biotite-almandine

(Fe,Mg)3Al2Si3O12)-ab or oligoclase


From: Turner 1968


Barrovian Metamoprhism• ___________ Zone

– qtz-misc-bio-almandine-staurolite-(oligoclase)• ___________ Zone

– qtz-bio-misc-oligoclase-almandine-kyanite• ___________ Zone

– qtz-bio-misc-oligoclase-almandine-sillimanite• Zones were mapped in a small portion of

Aberdeenshire and latter extended across the full length of the Highlands.


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From: Turner 1968


Extension of Barrow’s Zones along the extent of the Dalradian in Scotland

Highland Boundary Fault

Great G

len F

ault

BuchanZones

Moinian

N

Newer GraniteChloriteBiotiteAlmandineAndalusiteKyaniteSillimanite

Dalradian Metamorphic Zones

0 50km

From: Turner 1968


Barrovian Metamoprhism• Some minerals, e.g., biotite, _______through

the higher grade zones, however others, e.g., staurolite, __________ in the next zone.

• A line on a map that corresponds to the first appearance of an index mineral is called an _________ (line of equal grade). Isograds can be drawn for each index mineral.

• Barrow's work led to our present concept of metamorphic grade, although the interpretation of the significance of the zones varies.


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Barrovian Metamoprhism• 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 – Regional Metamorphism.

• Tilley (1924) suggested that the isograds mark rocks originating under closely similar physical conditions of temperature and pressure - not greatly different from what we believe today.


P-T Grid for Dalradian

Stau

rolit

eZo

ne

Lower limit of staurolite

Temperature

Pres

sure

Upper limit of staurolite

Barrovian Metamoprhism

From: Turner 1968


Water saturatedgranite solidus

ChloriteZone

BiotiteZone

SillimaniteZone

KyaniteZone

Stau

rolit

eZo

ne

GarnetZone

Lower limit of biotite

Upper limit of kyanite

Lower limit of sillimanite

Lower limit of almandine

Lower limit of staurolite

Temperature

Pres

sure

Upper limit of staurolite

P-T Grid for Dalradian

Barrovian Metamoprhism

Path followed by Dalradian sequence during metamorphism

From: Turner 1968


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Barrovian Metamoprhism• The first appearance of an index or zone mineral

indicates a ________ metamorphic grade, as long as the rocks were of an appropriate ___________ for that mineral to grow.

• The appearance of a particular mineral depends on the following variables:– Conditions under which the _____________ occurred, i.e.,

temperature, water pressure, load pressure.– Rates of _________ and _______ involved in formation of

the mineral.– ____________ of the rock.

• The last variable is the most important factor in the production of a given mineral under different metamorphic conditions.


Facies• An isograd mapped within a single,

homogeneous layer closely approaches the idealized concept of a line of equal grade.

• Correlation of an isograd from one area with one mapped in a widely separated area, can in rocks of similar composition, be hazardous as each rock may have formed under different conditions at different times.


Facies• A Finnish geologist, Eskola, was the first to

attempt to correlate metamorphic zones between widely separated areas.

• Working in Finland, Eskola found that contact metamorphic assemblages were related to grade and composition.

• When he compared his results to others he found that some mineral assemblages were the same between areas, while others in rocks of similar composition were quite different.


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Facies• Led Eskola to speculate that if rocks from the

two different areas were metamorphosed under different conditions, e.g., P & T, they would respond differently

• This prompted him to propose a classification of metamorphic rocks:– ________ - an association of metamorphic rocks,

each consisting of a mineral assemblage consistently related to the composition of the rock.


Facies

Unmetamorphosed Rock

Facies A Facies B Facies C Facies D Facies E

Shale - Mudstone chlorite

muscovitealbitequartz

biotitechloritemuscovitealbitequartz

garnetbiotitemuscovitealbite*quartz

staurolitegarnetbiotiteplagioclase*quartz

sillimanitegarnetbiotiteplagioclasequartz

Slate or Phyllite

Phyllite or Schist Schist or Gneiss

Andesitic Volcanic Tuff

actinolitealbiteepidotechloritequartz

actinolitealbiteepidotechloritequartz

hornblendealbiteepidoteQuartz

hornblendeplagioclasequartz

hornblendeplagioclasequartz

Chlorite or Actinolite Schist AmphiboliteSandy Limestone or Siliceous Dolomite

dolomitecalcitequartz

tremolitecalcitequartz

tremolitecalciteQuartz

diopsidecalcitequartz

diopsidecalcitequartz

Marble Tremolite Marble Diopside Marble

Mineral assemblages for different facies of metamorphism, i.e. each facies represents the same T and P conditions, for three common lithologies

* - plagioclase composition changes from albite ( <An10) to oligoclase-andesine (An20 to An 40)


Facies• Table shows the relationship between

metamorphic zones and metamorphic facies. Not only for pelitic rocks as mapped by Barrow, but also for Basic and Calcareous rocks.

• If all the rock types in the table were interbedded correlation of the mineral assemblages within each rock type would be very simple.

• Such a correlation, for several rock types within a single metamorphic grade, defines the metamorphic facies for that grade.

types of metamorphism - brock university · types of metamorphism ... in very large belts...

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