Download Metamorphic Rocks

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Transcript
Learning Goal: Understand how metamorphic rocks are formed and classified.
 S6E5.
Students will investigate
the scientific view of how the
earth’s surface is formed
 c. Classify (group) rocks
(metamorphic) by their process
of formation (formed)
 Rocks that have changed (metamorphism) due
to HEAT and PRESSURE.
These rocks form
DEEP underground!
Magma heats up surrounding
rock.
Pressure from plate movement
folds and buckles the crust.


Metamorphic rocks are formed by the effect of
heat and pressure on existing rocks.
This can greatly affect the hardness, texture or
layer patterns of the rocks.
Pressure from surface
rocks
metamorphic
rock
forming
here
Magma
heat

Metamorphic rocks are classified by texture in 2
ways…
1.Foliated
2.Non-Foliated

The processes of compaction and recrystallization change the
texture of rocks during metamorphism.

Compaction
The grains move closer together.
The rock becomes more dense.
Porosity is reduced.
 Example: clay to shale to slate

Recrystallization
Growth of new crystals. No changes in overall chemistry.
New crystals grow from the minerals already present. A
preferred orientation of minerals commonly develops under
applied pressure. Platy or sheet-like minerals such as
muscovite and biotite become oriented perpendicular to the
direction of force. This preferred orientation is called
foliation.

Mineral grains flatten and line up in parallel
bands OR layers.
That are formed under directed
Slate:
Foliated (with layers)
pressure
Gneiss:
Foliated (with
banding)
Foliated Texture
Foliated
Foliated Textures
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
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

Mineral grains change, grow, and rearrange,
but don’t form bands or layers.
Formed under uniform
Quartzite
pressures
Marble
Non-foliated Rocks Examples
•
Marble:
- metamorphosed
limestone
Quartzite forms in two different ways.
pressures
•
•
and --temperatures of deep burial,
In the first way, under the high
sandstone
Quartzite:
metamorphosed
sandstone
Metamorphic Zones
Metamorphic Zones
• Metamorphism is common along most plate boundaries like this.
The Types of Metamorphism
Read this slide
Then use the next two sides to
complete the chart
Regional Orogenic Metamorphism is the type of
metamorphism associated with convergent
plate margins
• Dynamo-thermal: one or more episodes of
orogeny with combined elevated geothermal
gradients and deformation (deviatoric stress)
• Foliated rocks are a characteristic product
Types of metamorphism
Regional
Shock
metamorphism
metamorphism
Depth,
km
0
Regional
high-pressure
metamorphism
Contact
metamorphism
Regional
metamorphism
Oceanic
crust
35
Oceanic
lithosphere
75
Water
Seafloor
metamorphism
Types of metamorphism
Shock
metamorphism
Regional
metamorphism
Regional
high-pressure
metamorphism
Contact
metamorphism
Regional
metamorphism
Depth,
km
0
Oceanic
crust
35
Oceanic
lithosphere
75
Burial
metamorphism
Heat
Pressure
Pressure Sedimentary
Sedimentary Igneous
IgneousPressure
or Metamorphic
or Metamorphic Rock
Metamorphism
Effect
G
r
a
i
Classification
based on Texture
s
n
Foliated
Nonfoliated
Heat & Pressure
NO
↑ Flatten
Grains ↑
Layers
Bands
Layers
Slate
Phyllite
Schist
Gneiss
HEAT
Bands
PRESSURE
Slate
Gneiss
Quartzite
Marble
Learning Goal: Understand how metamorphic
rocks are formed and classified.
Do Now Q: What features do foliate metamorphic
rocks show?