FACTORS INFLUENCING METAMORPHISM

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FACTORS INFLUENCING METAMORPHISM
PRESSURE
More pressure is exerted on rocks at depth than
at Earths surface. LITHOSTATIC or CONFINING
PRESSURE pushes on rocks in all
directions. Grains become smaller and denser
at depth.
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FACTORS INFLUENCING METAMORPHISM
PRESSURE
Pressure is greatest at the contact point
between grains. Bonds can break. Ions migrate
and re-bond. Rock becomes compressed.
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FACTORS INFLUENCING METAMORPHISM
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.
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FACTORS INFLUENCING METAMORPHISM
PRESSURE
Causes existing minerals and features to
deform. Doesnt affect minerals in the
rocks. Induces FOLIATION, in which the tabular
minerals are aligned ? to the direction
of greatest directed pressure.
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FACTORS INFLUENCING METAMORPHISM
FOLIATION
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FACTORS INFLUENCING METAMORPHISM
PRESSURE
For metamorphism to occur, 1 kilobar of pressure
is required. 1 Bar pressure applied to the
Earths 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.
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FACTORS INFLUENCING METAMORPHISM
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
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FACTORS INFLUENCING METAMORPHISM
CIRCULATING FLUIDS
Influence production of new minerals by ionic
exchange. Speed up reactions and change
overall composition of the rock.
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FACTORS INFLUENCING METAMORPHISM
PARENT ROCK
Composition of parent rock influences the type of
metamorphic rock produced.
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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.
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CONTACT METAMORPHISM
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. Diffe
rences in temperature is also significant.
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CONTACT METAMORPHISM
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REGIONAL METAMORPHISM
Alters rocks over a large geographic
region. Appalachians of New England North
Cascades of Washington-British Columbia
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REGIONAL METAMORPHISM
BURIAL METAMORPHISM
Occurs deep in sedimentary basins. Requires
depths gt 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.
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REGIONAL METAMORPHISM
BURIAL METAMORPHISM
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REGIONAL 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.
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REGIONAL METAMORPHISM
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 doesnt reverse itself.
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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.
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OTHER TYPES OF METAMORPHISM
FAULT ZONE METAMORPISM
Produced by rocks grinding past each other at a
fault. Produced by directed pressure and
frictional heat.
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OTHER TYPES OF METAMORPHISM
SHOCK METAMORPISM
Produced by meteorite impact. Forms shock
varieties of quartz.
Stishovite
Coesite
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OTHER TYPES OF METAMORPHISM
PRYOMETAMORPHISM
Results from ultra-high temperatures that occur
in low pressure environments. Usually produced
by lightning hitting surface rocks or sediments.
Fulgurite
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OTHER TYPES OF METAMORPHISM
PRYOMETAMORPHISM
Fulgurite