Metamorphic Rocks
Definitions
•
Metamorphic Rock
- "Meta"= Change (Grk)
- "Morph"= form (Grk)
-- a rock that
has been changed
from its original form ( parent ) by
heat , pressure , and fluid activity
into a new rock ( daughter ).
Heat
Sources
Sources Include.....
Include.....
Magma
•• Magma
-- temperature
temperature of
of magma
magma
-- composition
composition of
of magma
magma
Geothermal gradient
gradient
•• Geothermal
-- temperature
temperature increases
increases with
with depth
depth of
of burial
burial
-- core
core of
of Earth
Earth is
is warmer
warmer than
than outer
outer crust
crust
Uniform
Pressure
vs Directed Pressure
Uniform
Pressure
Lithostatic
•• Lithostatic
-- "Lithos"=
"Lithos"= rock,
rock, static=
static= unchanged
unchanged (pressure)
(pressure)
-- uniform
uniform (aka
(aka non-directed)
non-directed)
-- equal
equal intensity
intensity from
from all
all directions
directions by
by rocks
rocks
Directed Pressure
one direction of squeezing is much stronger
than the others
Minerals align themselves to reduce stress.
Types of Metamorphism
Contact
•• Contact
-- caused
caused by
by igneous
igneous activity
activity
Dynamic
•• Dynamic
-- aka
aka cataclastic
cataclastic
-- associated
associated with
with faults
faults &
& earthquake
earthquake zones
zones
Regional
•• Regional
-- caused
caused by
by tremendous
tremendous pressures
pressures
associated with
with tectonic
tectonic plate
plate activity
activity
associated
Contact Metamorphism
Igneous Intrusions
Intrusions
•• Igneous
-- size
size and
and type
type of
of magma
magma important
important
mafic magma
magma hotter
hotter than
than felsic
felsic
>>mafic
-- heat
heat decreases
decreases away
away from
from magma
magma
forms aa zone
zone of
of altered
altered country
country rocks
rocks called
called
>>forms
Aureoles
Aureoles
Sometimes creates a metamorphic rock called a
hornfels -in essence a “cooked” rock
Hornfels- basically any rock that has been “cooked”
and metamorphosed by contact with igneous material
(magma or lava).
Often original
rock textures
are identifiable
Dynamic Metamorphism
••
••
aka Cataclastic
Cataclastic Metamorphism
Metamorphism
aka
associated with
with Fault
Fault Zones
Zones
associated
-- Places
Places where
where the
the Earth's
Earth's crust
crust ruptured
ruptured
-- Rock
Rock pulverized
pulverized
heat and
and pressure
pressure come
come from
from movement
movement along
along the
the
>> heat
Fault
Fault
Mylonite
resultant rock
rock is
is known
known as
as aa Mylonite
•• resultant
Regional Metamorphism
Most common
common form
form of
of metamorphism
metamorphism
•• Most
caused by
by large
large scale
scale forces
forces
•• caused
-- lithospheric
lithospheric plate
plate collision
collision
covers very
very large
large areas
areas
•• covers
-- metamorphic
metamorphic belts
belts or
or zones
zones
-- Zones
Zones are
are characterized
characterized by
by
Index Minerals
Minerals
Index
form under
under specific
specific temperatures
temperatures and
and pressures
pressures
>>form
metamorphic facies
facies
>>metamorphic
commonly associated
associated with
with
•• commonly
-- shields:
areas areas
of crystalline
rocks rocks
Shields
andstable
Mountains:
of crystalline
Metamorphic Textures
Foliated
•• Foliated
-- Folios
Folios == page
page or
or leaf-like
leaf-like
-- rock
rock has
has distinct
distinct banding
banding or
or layering
layering
often not
not smooth
smooth like
like in
in sedimentary
sedimentary rocks
rocks
>>often
-- formed
formed under
under directed
directed pressure
pressure
Non-foliated
•• Non-foliated
-- no
no distinct
distinct layering
layering character
character
-- often
often aa massive
massive crystalline
crystalline texture
texture
-- formed
formed under
under uniform
uniform pressures
pressures
Foliated Texture
Foliated Textures
Slatey
•• Slatey
-- looks
looks like
like blackboard
blackboard
dull surface
surface
>>dull
-- smooth,
smooth, thin
thin layering
layering
-- breaks
breaks into
into flat
flat slabs
slabs
referred to
to as
as slatey
slatey cleavage
cleavage
>>referred
-- no
no mineral
mineral grains
grains visible
visible
Phyllitic
•• Phyllitic
-- looks
looks like
like waxed
waxed surface
surface
has aa "sheen"
"sheen" to
to itit
>>has
-- may
may have
have little
little "waves"
"waves" on
on
surface
surface
referred to
to as
as
>>referred
crenulations
crenulations
-- some
some small
small grains
grains visible
visible
Schistose
•• Schistose
-- distinct bands of minerals
-- visible
visible grains
mineral grains
garnets, staurolites
staurolites
>>garnets,
-- may
may have
have shiny
shiny
appearance
due to
to mica
mica minerals
minerals
>>due
Gneissic
•• Gneissic
-- larger
larger grains
grains
-- may
may look
look like
like igneous
igneous rock
rock
-- may
may have
have crude
crude banding
banding
intensely distorted
distorted
>>intensely
-- different
different minerals
minerals than
than
schistose
schistose
Foliated MM Rocks
slate
phyllite
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
schist
gneiss
MM
MM Rocks
Rocks that
that could
could form
form as
as aa shale
shale (sedimentary)
(sedimentary) parent
parent rock
rock is
is
exposed to increasing directed pressure and temperature
Migmatite- a very high grade metamorphic rock
that has begun to partially melt
Migmatite- note the “blobs” of quartz
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Non-foliated
textured
Non-foliated
RocksMM Rocks
• Marble:
- metamorphosed
limestone
Quartzite:
•• Quartzite:
-- metamorphosed
metamorphosed
quartz sandstone
sandstone
quartz
Environment of Formation- EOF
look for specific minerals and textures
Map out where those minerals are found
reconstruct T & P for given minerals
Find a modern setting that has similar T & P
using Uniformitarianism
Metamorphic Zones
Metamorphic Zones-Map
Zones-Map
Metamorphic
Metamorphic Facies
distinctive metamorphic mineral assemblages that occur in welldefined P & T regions and named after the key rocks (and
associated lithologies) found
Hornfels
Metamorphic Zones
• Metamorphism is common along most plate boundaries like this.