Metamorphic Rocks
Metamorphic Rock
• “Meta” means Change
• “Morph” means Form
• Definition: A
sedimentary/igneous/metamorphic rock that
has been changed from its original form by
heat, pressure, and/or fluid activity, into a new
rock.
Formation of Metamorphic Rock
• Previously existing rock (parent rock) usually
recrystallized.
• Recrystalization is the process of increasing
the size of the minerals crystals or rock clasts
and/or changing the mineral composition
without melting.
• 2 ways of recrystalizing parent rock.
– Contact metamorphism
– Regional metamorphism
Contact Metamorphism
• When older rocks come in contact with the
magma of an intrusion or lava of an extrusion ,
the heat and mineral fluids of the liquid rock
alter the older rock.
Characteristics of Contact
Metamorphism
Magma
Metamorphic rock
Parent Rock
Metamorphic rock
• In the contact metamorphism zone there will
be 3 distinct layers
Parent Rock
Parent rock changed to metamorphic rock
Regional Metamorphism
• Colliding tectonic plates often result in mountain
building. The closer an area is to the boundary of
the colliding plates, the greater the increase in
temperature and pressure.
• The increase in temperature and pressure
transforms older rocks to a series of
metamorphic rocks.
• This is called Regional metamorphism, because it
takes place over a large region of the earth.
Regional Metamorphism
Regional Metamorphism
Textures of Metamorphic Rocks
• 2 major types of textures
• Foliated
• Non-foliated
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
Banding vs Layering
Which texture banding or layering?
Which texture banding or layering?
Foliated rocks
• These rocks have layers of minerals crystals
that have formed by recrystallization usually
under regional metamorphism
• These rocks are composed of two or more
minerals and are made of interconnected
mineral crystals.
• There are 4 types of foliations
Foliated Textures
• Slate
• Schist
- looks like blackboard
- distinct bands of minerals
- visible mineral grains
> dull surface
- smooth, thin layering
- breaks into flat slabs
> garnets, staurolites
- may have shiny
appearance
> referred to as slatey cleavage
- no mineral grains visible
• Phyllite
- looks like waxed surface
> has a "sheen" to it
- may have little "waves" on
surface
-- some small grains visible
> due to mica minerals
•
Gneiss
- larger grains
- may look like igneous rock
- may have crude banding
> intensely distorted
- different minerals than
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 metamorphic rocks
• These rocks are not layered because the
minerals are not flat, or sheet like, and/or the
rocks were not subjected to directional
pressure.
• These rocks are composed of interconnected
mineral crystals
Non-foliated Rocks
• Marble:
- metamorphosed
limestone
Quartzite:
•• Quartzite:
-- metamorphosed
metamorphosed
quartz sandstone
sandstone
quartz