Metamorphic and types of the Metamorphism

METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURE
More pressure is exerted on
rocks at depth than at
Earth’s surface.
LITHOSTATIC or
CONFINING PRESSURE
pushes on rocks in all
directions.
Grains become smaller and
denser at depth.

PRESSURE
Pressure is greatest at the
contact point between
grains.
Bonds can break.
Ions migrate and re-bond.
Rock becomes
compressed.

PRESSURE
Pressure may be greater in
some directions.
DIRECTED PRESSURE
Flattens rock in the
direction at which the
greatest pressure is
applied.
Lengthens rock in the
direction  to the
greatest pressure.

PRESSURE
Causes existing minerals and
features to deform.
Doesn’t affect minerals in
the rocks.
Induces FOLIATION,
in which the tabular
minerals are aligned
 to the direction of
greatest directed
pressure.

FOLIATION

PRESSURE
For metamorphism to occur, 1 kilobar of pressure is
required.
1 Bar = pressure applied to the Earth’s surface
by the atmosphere.
1 Bar = 1.02 kg/cm2
1 kilobar = 1000 Bar (or 1020 kg/ cm2
)
These pressures occur at ~ 3 km depth.

CIRCULATING FLUIDS
Water greatly influences metamorphism.
Aids in migration of unbonded atoms and ions.
Allows for exchange of ions between adjacent grains.
Water comes from a variety of sources
Ground water
Subducted oceanic crust
Crystallization of magma
Decomposition of water-rich minerals like
amphiboles and clays

CIRCULATING FLUIDS
Influence production of new minerals by ionic
exchange.
Speed up reactions and change overall composition
of the rock.

PARENT ROCK
Composition of parent rock influences the type of
metamorphic rock produced.

TYPES OF METAMORPHISM
CONTACT METAMORPHISM
Solid rocks in close proximity to magma will change
in response to heating and circulation of hot
fluids, i.e., INTRUSIONS.
Produces a “baked zone” in the adjacent country rock.
Pressure is not significant in reaction.
Impact of the intrusion is local.
Only rocks in immediate contact with the intrusion
will be highly metamorphosed.

Minerals stable at high temperatures will be formed
closest to the intrusion.
Coarser grained metamorphic minerals will also be
formed closest to the intrusion.
Size of the intrusion also influences the amount of
metamorphism.
Differences in temperature is also significant.

REGIONAL METAMORPHISM
Alters rocks over a large geographic region.
Appalachians of New England
North Cascades of Washington-British Columbia

BURIAL METAMORPHISM
Occurs deep in sedimentary basins.
Requires depths > 10 km
At these depths and greater, lithostatic pressure and
geothermal heat drive metamorphic reactions and
recrystallization.
Does not require a tectonic process.
Does not create mountain belts.
Generally no foliation because no directed pressure.

BURIAL METAMORPHISM

DYNAMOTHERMAL METAMORPHISM
Affected by pressure (squeezing) and heat (magma).
Occurs when converging plates squeeze rock caught
between the plates.
Crust generally thickens.
Surface rocks get taken deep into the Earth.
Rocks are subjected to high temperatures, lithostatic
pressure and directed pressure.
Rocks become foliated.

DYNAMOTHERMAL METAMORPHISM
Produced metamorphic rocks found in the Alps,
Himalaya, and Appalachian Mountains.
Also produced the greatly eroded metamorphic rocks
in the Great Lakes region.
These rocks are exposed by uplift (faulting) and rapid
erosion.
The process doesn’t reverse itself.

OTHER TYPES OF METAMORPHISM
HYDROTHERMAL METAMORPISM
Chemical alteration of pre-existing rocks by hot water.
Occurs primarily beneath ocean floor near divergent
plate boundaries.
Creates water-rich minerals.
Includes serpentine, talc, and chlorite
In addition, when steam hits ocean water and cools
rapidly, valuable metals such as Cu, Ni, Fe and
Pb are precipitated.

FAULT ZONE METAMORPISM
Produced by rocks grinding past each other at a fault.
Produced by directed pressure and frictional heat.

SHOCK METAMORPISM
Produced by meteorite impact.
Forms shock varieties of quartz.
Stishovite
Coesite

PRYOMETAMORPHISM
Results from ultra-high temperatures that occur in low
pressure environments.
Usually produced by lightning hitting surface rocks or
sediments.
Fulgurite

PRYOMETAMORPHISM
Fulgurite

Metamorphic and types of the Metamorphism

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