Download Metamorphic_Rocks

METAMORPHIC ROCKS
Rocks that form from other pre-existing rock
(sedimentary, igneous, or metamorphic) which have been
changed from high pressure and/or high
temperature (P/T).
Metamorphic Rocks
Metamorphic Rocks Formation
Metamorphic Rocks
Definitions
Definitions
•
Metamorphic Rock
- "Meta"= Change (Grk)
- "Morph"= form (Grk)
-- a rock that
has
has been
been changed
changed
from its original form ( parent ) by
heat , pressure , and fluid activity
into a new rock ( daughter ).
Conditions that cause rock to undergo
metamorphism include:
• Heat - Under conditions of high temperature
from magma contacting pre-existing rock.
• Pressure - Deep burial and pressure from
mountain formation.
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
Lithostatic
•• Lithostatic
"Lithos” =rock,
rock,static=
static =unchanged
unchanged(pressure)
(pressure)
-- "Lithos"=
uniform (aka
(aka non-directed)
non-directed)
-- uniform
-- 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
1. Contact Metamorphism
2. Regional Metamorphism
Contact Metamorphism

Deep burial and pressure from mountain
formation (at least several kilometers).

The main metamorphic agent is heat.

Also forms when pre-existing rock comes into
contact with molten lava or magma. The
heat from the molten material is hot enough
to cause the minerals in the original rock to
re-crystallize, but not melt.
Regional Metamorphism

Most common form of metamorphism

Covers large areas typically associated with
mountains

Deep burial and pressure from mountain formation.

commonly associated with Shields and
Mountains: areas of crystalline rocks

Heat and Pressure change the rock.
Regional Metamorphism
Most common
common form
form of
of metamorphism
metamorphism
•• Most
caused by
by large
large scale
scale forces
forces
•• caused
lithospheric plate
plate collision
collision
-- lithospheric
covers very
very large
large areas
areas
•• covers
-- metamorphic
metamorphic belts
belts or
or zones
zones
Zones are
are characterized
characterized by
by
-- Zones
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
Shields of the World
Types of Metamorphic Rocks

Foliated: rocks with mineral crystals arranged in
cable-like distorted layers/structures
Mineral Alignment
 Banding
 Animation: Foliation


Nonfoliated: rocks with recrystallized minerals;
no layering

Recrystallization: This is the growth of new mineral
crystals from other rocks.
Foliated Texture
Foliated Textures
Slatey
•• Slatey
Schistose
•• Schistose
-- 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
garnets, staurolites
staurolites
>>garnets,
-- may
may have
have shiny
shiny
appearance
due to
to mica
mica minerals
minerals
>>due
Gneissic
•• Gneissic
-- 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
-- distinct bands of minerals
-- visible
visible grains
mineral grains
crenulations
crenulations
-- some
some small
small grains
grains visible
visible
-- 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
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
Non-foliated Rocks
• Marble:
- metamorphosed
limestone
Quartzite:
•• Quartzite:
-- metamorphosed
metamorphosed
quartz sandstone
sandstone
quartz
Scheme for Metamorphic Rock Identification
MINERAL
ALIGNMENT
BANDING
FOLIATED
Texture
Type of
Metamorphism
Comment
Regional
Mica
Low-Grade
metamorphism of
SHALE
Mica, Quartz,
Feldspar,
Amphiboles, Garnet
Foliation surfaces shiny
from microscopic mica
crystals
Composition
Mica, Quartz,
Feldspar,
Amphiboles, Garnet,
Pyroxene
Mica, Quartz,
Feldspar,
Amphiboles, Garnet,
Pyroxene
(Heat and
Pressure
increase
w/depth)
Platy mica crystals
visible
Compact, may split
easily
Rock Name
Slate
Phyllite
Schist
Gneiss
Progression of Metamorphism
Start with a shale and then hit
it with heat and pressure!
More
Heat
&
Pressure
Rock Name
Rock Type
Grade of
Metamorphism
Shale
Sedimentary
-----
Slate
Metamorphic
Low
Phyllite
Metamorphic
Low/Intermediate
Schist
Metamorphic
Intermediate/High
Gneiss
Metamorphic
High
Molten Rock
Cools into
Igneous Rock
-----
Shale
(Sedimentary Rock)
Heat
&
Pressure
Slate
(Metamorphic Rock)
Slate
(Metamorphic Rock)
Heat
&
Pressure
Phyllite
(Metamorphic Rock)
Phyllite
(Metamorphic Rock)
Heat
&
Pressure
Schist
(Metamorphic Rock)
With even more heat & pressure
(High-Grade Metamorphism)
… you end up with something
that is really Gneiss!
Scheme for Metamorphic Rock Identification
Texture
Composition
NONFOLIATED
Variable
Type of
Metamorphism
Contact
Regional
Calcite and/or
Dolomite
(Heat
&
Pressure)
Rock Name
Various rocks changed
by nearby magma/lava
Hornfels
Metamorphism of
Quartz Sandstone
Quartzite
(Heat)
Quartz
Various minerals in
particles and matrix
Comment
Metamorphism of
Limestone or
Dolostone
Pebbles may be
distorted or stretched
Marble
Metaconglomerate

Animation: Metamorphic Rock Scheme
Where are metamorphic rocks found?

At the interface between igneous and
sedimentary rocks
• Mountainous regions
Metamorphic Zones
Metamorphic Facies
distinctive metamorphic
metamorphic lithologies
lithologies that
that occur
occur in
in well
well
•• distinctive
defined areas
areas and
and named
named after
after the
the key
key rocks
rocks found
found
defined
THE ROCK CYCLE
How are rocks classified?
IGNEOUS
Solidification
MAGMA
IGNEOUS
Plutonic
Solidification
MAGMA
Volcanic
IGNEOUS
Plutonic
Solidification
MAGMA
Weathering &
Erosion
Uplift
Volcanic
IGNEOUS
Plutonic
Solidification
MAGMA
SEDIMENT
Weathering &
Erosion
Volcanic
IGNEOUS
Plutonic
Solidification
MAGMA
SEDIMENT
Weathering &
Erosion
Erosion
Transport
Deposition
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Solidification
MAGMA
SEDIMENT
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Solidification
MAGMA
SEDIMENT
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Increased P&T
METAMORPHIC
Solidification
MAGMA
SEDIMENT
Weathering &
Erosion
Deposition
Burial/Compaction
Volcanic
Can you see
IGNEOUS
any shortcuts?
Cementation
SEDIMENTARY
Plutonic
Increased P&T
METAMORPHIC
Solidification
Melting
MAGMA
SEDIMENT
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Increased P&T
METAMORPHIC
Solidification
Melting
MAGMA