Download Types of Metamorphism Regional Metamorphism

ERSC 3P21 Metamorphic Petrology II
03/11/2005
Types of Metamorphism
•
•
•
•
•
_________________________
_________________________
_________________________
_________________________
_________________________
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
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 granitic and/or ultramafic masses
intruded into the terranes generally, but not
always near the thermal axis.
ERSC 3P21 - Brock University
Greg Finn
1
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Regional Metamorphism
At point A temperature = 400°C, pressure = 3.5 kbars
ERSC 3P21 - Brock University
Greg Finn
From: Marshak 2001
Sugluk
Superior Province
Cape
Smith
Belt
Subprovince Types
Minto
La
or
ad
br
Hudson Bay
ou
Tr
i to
ba
ar
io
Trans - Hudson
Orogen
M
Ashuanipi
Bienville
O
Volcanic
nt
an
Thompson
Belt
gh
High Grade
Pikwitonei
La Grande R.
Plutonic
Winisk
Sachigo
James
Bay
Opinica R.
N
Metasedimentary
Berens River
Uchi
Bird River
Nemiscau R.
English River
Wabigoon
Opatica
Quetico
Wawa
Quetico
sin
g
Winnipeg River
Ka
pus
ka
Canada
U.S.A.
Abitibi
Pontiac
Grenville
Province
Wawa
Quebec
Southern Province
Ontario
Minnesota
River Valley
St. Catharines
0
250 Km
ERSC 3P21 - Brock University
Greg Finn
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
ERSC 3P21 - Brock University
Greg Finn
2
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Contact
Metamorphism
ERSC 3P21 - Brock University
Greg Finn
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 Finn
http://www.gpc.edu/~janderso/images/metafaci.jpg
ERSC 3P21 - Brock University
Greg Finn
3
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Pyro-metamorphism
• Recrystallization at high __________ of
xenolith fragments in volcanic rocks or
small intrusions
• Melting of the xenolith may occur
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
Hydrothermal Metamorphism
• Hydrothermal metamorphism results in
alteration to such _______ rich hydrous
minerals as talc, chlorite, serpentine,
actinolite, tremolite, zeolites, and clay
minerals.
• Rich ore deposits are often formed as a
result of hydrothermal metamorphism.
ERSC 3P21 - Brock University
Greg Finn
4
03/11/2005
http://www.pbs.org/wgbh/nova/abyss/frontier/images/chron10.jpeg
ERSC 3P21 Metamorphic Petrology II
http://earthsci.org/energy/geomin/kuroko.gif
ERSC 3P21 - Brock University
http://www.nmm.ac.uk/uploads/jpg/black_smoker.jpg
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
Cataclastic
Metamorphism
ERSC 3P21 - Brock University
From: Marshak 2001
Greg Finn
5
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Compositional Groups
• Loose groupings of metamorphic rocks
based on the original ________
composition
– Mudstones Î
– Basic Rocks Î
– Ultramafics Î
– Calcareous Î
– Granites
Î
Pelites
Metabasites
Ultramafics
Marbles
Granites
ERSC 3P21 - Brock University
Greg Finn
Pelites
• Derived from ________ sediments (mudstones)
• Characterized by high _____ and ______ contents,
which result in abundant _______ produced during
metamorphism
– Muscovite - common in low temp pelites
– Biotite - common in higher temp 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
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Greg Finn
kyanite muscovite schist
garnet biotite schist
biotite schist
Garnet muscovite schist
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Greg Finn
6
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Pelite
mu
st
mu
q
q
bi
bi
st
mu
mu
a
st
q
gt
q
gt
q
b
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)
ERSC 3P21 - Brock University
Greg Finn
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
ERSC 3P21 - Brock University
Greg Finn
Metabasite
hb
hb
cpx
cpx
hb
hb
p
p
cpx
cpx
p
op
p
a
b
p
p
op
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)
ERSC 3P21 - Brock University
Greg Finn
7
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Barrovian Metamoprhism
Dalradian
Moinian
Lewisian and
Torridonian
N
50
0
Moin
e Th
rust
Scale, km
Buchan
Zones
Fa
ult
Inverness
re
a
tG
len
Aberdeen
G
• 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.
r
da
un
Bo
nd
hla
Hig
yF
lt
au
Area investigated
by Barrow
ERSC 3P21 - Brock University
Greg Finn
Barrovian Metamoprhism
• Within the Dalradian sequence, Barrow
recognized the existence of
unmetamorphosed shale (pelite) which
subsequently underwent metamorphism.
• Barrow recognized a series of zones of
progressive metamorphism
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
8
ERSC 3P21 Metamorphic Petrology II
03/11/2005
Barrovian Metamoprhism
The 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
ERSC 3P21 - Brock University
Greg Finn
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
9
ERSC 3P21 Metamorphic Petrology II
03/11/2005
ERSC 3P21 - Brock University
Greg Finn
Dalradian Metamorphic Zones
Newer Granite
Chlorite
Biotite
Almandine
Andalusite
Kyanite
Sillimanite
Moinian
G
re
at
G
le
n
Fa
ul
t
Buchan
Zones
Extension of
Barrow’s Zones
along the extent
of the Dalradian
in Scotland
Hi
gh
ar y
nd
ou
B
d
lan
0
Fa
ult
N
km
50
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
10
ERSC 3P21 Metamorphic Petrology II
03/11/2005
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.
ERSC 3P21 - Brock University
Greg Finn
Barrovian Metamoprhism
P-T Grid for
Dalradian
Upper limit
of staurolite
Pressure
Staurolite
Zone
Lower limit
of staurolite
Temperature
ERSC 3P21 - Brock University
Greg Finn
Barrovian Metamoprhism
Pressure
Lower limit
of biotite
Garnet
Zone
Upper limit
of staurolite
Staurolite
Zone
Lower limit
of staurolite
Kyanite
Zone
Lower limit
of sillimanite
Path followed by
Dalradian
sequence during
metamorphism
Chlorite
Zone
Biotite
Zone
Lower limit
of almandine
P-T Grid for
Dalradian
Upper limit
of kyanite
Sillimanite
Zone
Temperature
Water saturated
granite solidus
ERSC 3P21 - Brock University
Greg Finn
11
ERSC 3P21 Metamorphic Petrology II
03/11/2005
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.
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
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.
ERSC 3P21 - Brock University
Greg Finn
12
ERSC 3P21 Metamorphic Petrology II
03/11/2005
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.
ERSC 3P21 - Brock University
Greg Finn
Facies
Mineral assemblages for different facies of metamorphism, i.e. each facies
represents the same T and P conditions, for three common lithologies
Unmetamorphosed
Rock
Shale - Mudstone
Facies A
chlorite
muscovite
albite
quartz
Slate or
Phyllite
Andesitic Volcanic
Tuff
actinolite
albite
epidote
chlorite
quartz
Sandy Limestone or
Siliceous Dolomite
dolomite
calcite
quartz
Facies B
biotite
chlorite
muscovite
albite
quartz
Facies C
garnet
biotite
muscovite
albite*
quartz
staurolite
garnet
biotite
plagioclase*
quartz
Phyllite or Schist
actinolite
albite
epidote
chlorite
quartz
tremolite
calcite
quartz
Facies E
sillimanite
garnet
biotite
plagioclase
quartz
Schist or Gneiss
hornblende
albite
epidote
Quartz
hornblende
plagioclase
quartz
tremolite
calcite
Quartz
diopside
calcite
quartz
Chlorite or Actinolite Schist
Marble
Facies D
hornblende
plagioclase
quartz
Amphibolite
Tremolite Marble
diopside
calcite
quartz
Diopside
Marble
ERSC 3P21
- Brock University
Greg Finn
* - 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.
ERSC 3P21 - Brock University
Greg Finn
13