Uniform pressure vs directed pressure

Metamorphic Rocks
Definitions

• Metamorphic

Rock

- "Meta"=
"Meta"= Change
Change(Grk)
- "Morph"=
"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 buria
buria
-- 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"= 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
Contact
•• Contact

caused by
by igneous
igneous activity
activity
-- caused

Dynamic
•• Dynamic

aka cataclastic
cataclastic
-- aka
associated with
with faults
faults &
& earthquake
earthquake zones
zones
-- associated

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
mafic magma

magma hotter
hotter than
than felsic
felsic
>

-- heat
heat decreases
decreases away
away from
from magma
magma
>forms
forms a
a zone
zone of
of altered
altered country
country rocks
rocks called
called
Aureoles
>
Aureoles

Sometimes creates a metamorphic rock called a
hornfels -in essence a “cooked” rock

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
heat and
and pressure
pressure come
come from
from movement
movement along
along the

the
>
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 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
Index Minerals
Minerals
-- Zones
Index
>form
form under
under specific
specific temperatures
temperatures and
and pressures
pressures
>
>metamorphic

metamorphic facies
facies
>

commonly associated
associated with
with
•• commonly

-- shields:
areas of
crystalline
rocks rocks
Shields
andstable
Mountains:
areas
of crystalline


Shields of the World


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
often not
not smooth
smooth like
like in
in sedimentary
sedimentary rocks
rocks
>

-- formed
formed under
under directed
directed pressure
pressure

Non-foliated
•• Non-foliated

-- no

no distinct
distinct layering
layering character
character
-- often
often a
a 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

Schistose

•• Schistose

-- distinct bands of minerals
-- visible
visible grains
mineral grains

>dull
dull surface
surface
>

-- smooth,
smooth, thin
thin layering
layering
-- breaks
breaks into
into flat
flat slabs
slabs

>garnets,
garnets, staurolites
staurolites
>

>referred
referred to
to as

as slatey
slatey cleavage
cleavage
>

-- no
no mineral
mineral grains
grains visible
visible

Phyllitic
•• Phyllitic

-- may
may have
have shiny
shiny
appearance

>due
due to
to mica
mica minerals
minerals
>

Gneissic
•• Gneissic

-- looks
looks like
like waxed
waxed surface
surface -- larger
larger grains
grains
>has
has a
a "sheen"
"sheen" to
to it
it
>
-- may
may look
look like
like igneous
igneous rock
rock
-- may
may have
have little
little "waves"
"waves" on
on- may
may have
have crude
crude banding
banding

surface
surface
>intensely
intensely distorted
distorted
>
>referred
referred to
to as
ascrenulations
crenulations
>
-- different
different minerals
minerals than
than
- some
some small
small grains
grains visible
visible
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


Environment of Formation- EOF
look for specific minerals
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
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


Metamorphic Zones
• Metamorphism is common along most plate boundaries like this.