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Transcript
Metamorphic Rocks
Metamorphism?
• Metamorphism from the
Greek μεταμορφώστε,
meaning “changing form”
– Is the solid-state
recrystallization of a preexisting rock (a “parent”
rock) though changes in
temperature, pressure,
and/or chemical conditions
– In layman’s terms: Cooking
and Squishing a rock
Reacting to Change…a Practical
Example
This is Bob→
Classroom
Temperature: 75 degrees F
Dressed the way he is now, Bob is adapted to his surroundings
Hawaii
Temperature: 95 degrees F
Dressed in a long-sleeved shirt and jeans, Bob overheats
In order to adapt to his new environment
a change of clothes is in order…
Bob is now adapted to his environment
Antarctica
Temperature: -129 degrees F
Dressed the way he was in Hawaii, Bob would freeze
to death In a matter of minutes
To adapt to his this new environment, another
Wardrobe change is needed
Though he can’t move,
Bob has adapted to his
environment
Minerals Behave similarly
• Every mineral has a stability range—of
Temperature and Pressure, that is
– Ex. Graphite and diamond
• Metamorphism occurs because each mineral
has a specific temperature/pressure/chemical
environment stability range
• Remember, these changes occur while the
rock is still solid
Making the Grade…
• Metamorphic grade—intensity of
metamorphism undergone by a rock
• Low grade
– High temp, low pressure--near surface
• High grade
– High temp, high pressure--deep under ground
Changes…
• Two types of changes
generally accompany
metamorphism
– Textural
• Changes in size and shape
and orientation of
minerals in a rock
– Mineralogical
• Decomposition of
unstable minerals and
crystallization of new
ones
Muscovite schist
Changes in Texture
Limestone
gneiss
marble
Foliation
• Texture change—
mineral alignment
perpendicular to
primary stress
– especially platy
minerals—like mica
• Any meta. rock lacking
foliation is said to be
non-foliated
Foliated or Non-foliated?
Non-foliated: marble
Foliated: gneiss
Changes in Minerology
Slate
Mostly clay minerals
Schist
Micas, quartz and garnet
More Jargon…w00t
• Four types of metamorphism
– “Burial”
– Contact
– Regional
– Hydrothermal
Burial Metamorphism
• The pseudometamorphism bordering
on witchcraft
• The absolute lowest
grade of metamorphism
• Caused by weight
(pressure) of overlying
rocks
• Creates non-foliated rocks
– Ex. Bituminous coal
Contact Metamorphism
• Rocks surrounding a
magma body literally
cook
• Creates non-foliated
rocks
• Highest grade occurs
next to the magma
body and decreases
with distance
Hydrothermal Metamorphism
• occurs when mineral
laden (and also, hot)
water reacts with rock,
changing the rock’s
composition
• Created non-foliated
rocks
– Ex. Black smoker
Regional Metamorphism
• Occurs in regions where
mountain building is
occurring
• Rocks are being heated
and deformed
• Produces rocks that are
foliated—banded or
layered
• Typical sequence as
grade increases