Download Igneous Textures and Classification

Igneous Texture and Classification
9/13/2005
Igneous Textures and
Classification
ERSC 2P17 Brock University
Igneous Textures
• The texture of a rock is defined as:
– ______________________________________
________________________________________
• In the case of the igneous rocks the texture
is largely determined by the______ ______
of the magma that resulted in the specimen
being examined
ERSC 2P17 Brock University
Igneous Textures
• Examining igneous rocks reveals that they
may consist of:
– ___________ grains which may be;
• large or small or a mixture of both
• _______________________________
– solid _________
• _______________________________
– individual ______ __________ packed together
• _______________________________
ERSC 2P17 Brock University
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Igneous Texture and Classification
9/13/2005
Igneous Textures
• The rate at which a magma cools controls:
–
–
• ___________________ = glassy
• ___________________ = crystalline
• ____________________= mix of both
ERSC 2P17 Brock University
Igneous Textures
• For slow cooling many mineral grains
________ and ______, with the rate of
cooling controlling the final size of the
mineral grains
• Grain size
– _______________ < 1 mm
• _______ (cannot be distinguished with unaided eye)
– _______________ 1-5 mm
• __________
– _______________ > 5 mm
• ___________
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Glassy =
Fast
Cooling
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Igneous Texture and Classification
9/13/2005
Fine Grained
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Medium Grained
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Coarse Grained
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3
Igneous Texture and Classification
9/13/2005
Coarse Grained
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Very Coarse Grained =
Very Slow Cooling
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Igneous Textures
• The degree of crystal development reflects
how a mineral nucleated and grew and the
ratio of solid to liquid at the time of growth
• Grain shape
– __________
• composed of good crystal faces
– __________
• some good crystal faces
– __________
• no good crystal faces
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4
Igneous Texture and Classification
9/13/2005
Euhedral
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Subhedral
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Anhedral
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5
Igneous Texture and Classification
9/13/2005
Igneous Textures
• Some igneous melts cool in two stages,
reflecting changes in the conditions under
which the magma exists
• Resulting rocks typically have two different
sizes of grains and are called ____________
• The large grains are referred to as
____________ and they are set in a finer
grained ___________
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Porphyritic Textures
_______________________
______________________
__________
________
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Porphyritic Textures
Large grains (Phenocrysts) in a finer grained matrix
Matrix
Phenocrysts
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6
Igneous Texture and Classification
9/13/2005
Porphyritic Textures
Large grains (Phenocrysts) in a finer grained matrix
Matrix
Phenocrysts
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Igneous Textures
• Vesicles - _________________
• Amygdules - ______________
Vesicles
Amygdules
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Plutonic Rock Types
(Intrusive Rocks)
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7
Igneous Texture and Classification
9/13/2005
Syenite
• Major Minerals:
– _____________
– _____________
• NO QUARTZ
• Accessories:
• ________, ________,
___________
Hornblende Syenite
Nepheline Syenite
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Granodiorite
PT-190
• Major Minerals:
– ______________
– ______________
• up to 10% quartz
• Accessories:
– ______, _________
BUPI 67
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Granite
BUPI 59
• Major Minerals:
– ____________
– ____________
– __________
• Accessories:
– ______, _________,
__________
2002-6
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8
Igneous Texture and Classification
9/13/2005
Gabbro
• Major Minerals:
– __________
– __________
• Accessories:
– _________, ______,
________
2000-2
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Ultramafic
• Major Minerals:
– _________
– _________
– _________
• Accessories:
– __________
PT-175
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Volcanic Rock Types
(Extrusive Rocks)
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9
Igneous Texture and Classification
9/13/2005
Rhyolite
• Major Minerals:
– _____________
– _____________
– ____________
86-1
• Accessories:
PI-4-2
– ______, _________,
_________
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Dacite
• Major Minerals:
– ___________
– ___________
– up to 15% ______
88-23
• Accessories:
– ______, _________,
__________
86-27
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Andesite
• Major Minerals:
– ___________
– ___________
– _______
86-72
• Accessories:
– _________
• Minor:
– ______,
_____________
86-73
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10
Igneous Texture and Classification
9/13/2005
Basalt
90-132
• Major Minerals:
– __________
– __________
– _______________
• Accessories:
– ______, _________
PT-96
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Ultramafic
• Major Minerals:
– __________
– __________
• Accessories:
– ______,
__________
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Simplified Classification of Igneous Rocks
Quartz > 5%
Fine
Rhyolite
No Quartz, No Feldspathoid
Coarse
Fine
Trachyte
Syenite
Feldspathoid > 5%
Coarse
Fine
Phonolite
Nepheline
Leucite
Syenite
Leucite
Phonolite
Syenite
Dacite
Monzonite
Latite
Nepheline
Monzonite
Tonalite
Quartz
Andesite
Monzodiorite
Latite
Basalt
Nepheline
Diorite
Quartz
Diorite
Andesite
Gabbro
Peridotite (ol
dominant)
Basalt
Nepheline
Gabbro
Tephrite
Pyroxenite
Hornblendite
Komatiite
Ijolite
Nephelinite
Feldspar
K-feldspar>
plagioclase
Coarse
Granite
Plagioclase>
K-feldspar
Granodiorite
Plagioclase
(oligoclase or
andesine)
Plagioclase
(labradorite
to anorthite)
No Feldspar
ERSC 2P17 Brock University
11
Igneous Texture and Classification
IUGS
Classification
of Igneous
Rocks
9/13/2005
Q
(2) With < 5% mafic minerals,
the rock is anorthosite. With
>40% mafic minerals, it is
typically gabbro. Rocks with
5-40% mafic minerals are
either diorite or
leucodiorite, and require
determination of the
plagioclase content with the
limiting composition being
An50.
90
Quartz-rich
granitic rocks
Pe
rce
nta
Granite
(3)
A
35
A
qtz lk-fe
sye ld.
nit
e
(1)
iorite
Percentage of Plagioclase
20
Alk-feld
syenite
(1) If biotite is the
dominant mafic mineral,
constituting < 10%, the
rock is termed a
Trondhjemite.
alite
Ton
(3)The type of
alkali feldspar
should be
specified if
possible, e.g.,
Microcline
granite.
nod
Gra
ge
Alk
of
aliQu
feld
art
spa
z
rg
ran
ite
60
90
65
Quartz
syenite
Quartz
monzonite
Syenite
Monzonite
Quartz diorite or
quartz gabbro (2)
Quartz
monzodiorite
or quartz
monzogabbro
Diorite or
gabbro
Monzodiorite or
monzogabbro
P
ERSC 2P17 Brock University
IUGS Classification of Igneous Rocks
Q
90
ua
rtz
Quartz-rich
granitic rocks
60
eo
fQ
(1) If biotite is the
dominant mafic mineral,
constituting < 10%, the
rock is termed a
Trondhjemite.
tag
ra n
ite
rce
n
rg
Pe
lds
pa
alife
Alk
35
A
qtz lk-fe
sy ld.
en
ite
(1 )
A
orite
nodi
Granite
Percentage of Plagioclase
20
Alk-feld
syenite
e
nalit
To
Gra
(3) The type of
alkali feldspar
should be
specified if
possible, e.g.,
Microcline
granite.
90
65
Quartz
syenite
Quartz
monzonite
Quartz
monzodiorite
or quartz
monzogabbro
Syenite
Monzonite
Monzodiorite or
monzogabbro
(3)
Diorite or
gabbro
P
Foid-bearing
monzodiorite or
monzogabbro
Foid-bearing
monzonite
Foid-bearing
syenite
Foid-bearing
alk-feldspar
syenite
Quartz diorite or
quartz gabbro (2)
35
Foid-bearing
diorite or
gabbro
r fo
te o
ite
en
sy
Foid monzodiorite
or foid monzogabbro
Fo
id d
iori
id
Fo
Foid
monzosyenite
id g
abb
ro
65
10
90
50
Foidilite
(as nephelinite, etc.)
The feldspathoid should
be specified in each rock
name; e.g., Nepheline
syenite
(4)
F (4)
(file=iugsclas.ds4)
Anorthosite
(plagioclasite)
ERSC 2P17 Brock University
Pl
Anorthosite
90
Gabbroic rocks
90
(leuco-)
plagioclase +
pyroxene + olivine
65
65
Olivine
Gabbronorite
Gabbronorite
IUGS
Classification
of Mafic
Igneous
Rocks
(2) With < 5% mafic minerals,
the rock is anorthosite. With
>40% mafic minerals, it is
typically gabbro. Rocks with
5-40% mafic minerals are
either diorite or
leucodiorite, and require
determination of the
plagioclase content with the
limiting composition being
An 50.
Troctolite
35
Gabbroids
35
(mela-)
10
10
Plag. bearing ultramafic rocks
Ultramafic rocks
Px
Ol
Pl
Gabbroic rocks
plagioclase +
orthopyroxene +
clinopyroxene
Pl
Gabbronorite
Norite
Gabbro
Plag.-bearing pyroxenites
Opx
Cpx
Pl
Anorthosite
(plagioclasite)
90
Anorthosite
90
Gabbroic rocks
(leuco-)
containing hornblende
65
Gabbronorite
65
Pyroxene hornblende
gabbronorite
35
Hornblende
gabbro
Gabbroids
35
(mela-)
10
Px
plag.-bearing 10
pyroxenite
plag.-bearing
hbl pyroxenite
10
plag.-bearing
px hornblendite
Hbl
10
plag.-bearing
hornblendite
Ultramafic rocks
(file=iugsclas.ds4)
ERSC 2P17
Brock University
12