Transcript Metamorphic Rocks

Metamorphic Rocks
Metamorphism
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Metamorphic rocks form from igneous or
sedimentary rocks which have been
exposed to heat and/or pressure.
Metamorphism occurs when heat and
pressure break some of the bonds in the
minerals, but not enough to melt the rock.
There are 3 main agents that cause
metamorphism: heat, pressure, and
circulating fluids.
Heat
Metamorphism triggered by a change in
temperature is caused when:
 A rock moves to a greater depth (and hence,
warmer temps) by tectonic movement or deep
burial under sedimentary deposits, or
 Magma rises up intrusively and “bakes” the
surrounding rock
 Magma creates what is known as contact
metamorphism
Pressure
Metamorphism is triggered by a change in
pressure, caused when:
 A rock is deeply buried under sedimentary
deposits, or
 Tectonic plates slide or collide, exposing rocks
at the plate boundaries to extreme pressure
 This can create mountains and is known as
regional metamorphism
Pressure
There are two kinds of pressure:
 Confining pressure pushes on rocks equally
from all directions, compressing them and
reducing their size, or
 Directed pressure pushes on rocks greater in
one direction than the other. This tends to bend
or stretch the rock and align its minerals in the
direction of the pressure. This alignment is
called foliation.
Confining Pressure
Circulating Fluids
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Fluids (usually water) circulate
underground and drive metamorphism by
either speeding up the movement of a
rock’s own elements or by adding or
removing ions to change the overall
composition of the rock.
Limestone is a
sedimentary rock.
When exposed to heat
and pressure, limestone
metamorphoses into
marble.
Shale is a sedimentary
rock.
When exposed to heat
and pressure, shale
metamorphoses into
slate.
Sandstone is a
sedimentary rock.
When exposed to heat
and pressure, sandstone
metamorphoses into
quartzite.
Coal is a sedimentary
rock.
When exposed to heat
and pressure, coal
metamorphoses into
anthracite.
Granite is an igneous
rock.
When exposed to heat
and pressure, granite
metamorphoses into
gneiss.
Talc is a silicate mineral
When exposed to heat
and pressure, talc
minerals metamorphoses
into soapstone.
Basalt is an igneous
rock.
When exposed to heat
and pressure, basalt
metamorphoses into
schist.
3 Main Metamorphic Environments
High
temperature/low
pressure
Low
temperature/high
pressure
High
temperature/high
pressure