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Geology
Exam 1
Igneous Rocks
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What makes up large parts of the continent and oceanic rocks?
Igneous Rocks
The common rocks are
igneous
rocks
Igneous rocks indicate
plate boundaries
and
hot spots.
What is a magma?
A
molten rock
below the
earth’s surface.
Magma
solidifies
into
plutonic
/
intrusive igneous
rock.
Magma erupts as either
lava
/
pyroclastic
materials.
Pyroclastic
materials and
lava
cool to form
volcanic
(extrusive)
igneous
rocks.
What is viscosity?
Resistance
to
flow.
What controls viscosity?
Primarily controlled by
temperature
and
composition.
Higher temperature=
lower
viscosity. Lowe temperature=
higher
viscosity.
UMIF
Ultramafic
have the
least silica
and
high Fe
and
Mg
Mafic
have
less silica
and
Fe
and
Mg Rich
Intermediate
is between
felsic
and mafic
Felsic
is
silica-rich
and
low
in Fe and
Mg
Low viscosity
(mafic) is runny because of
higher temperature
and
less silica content.
High viscosity
(felsic) is
thick
because of
lower temperature
and
higher silica content.
Patrial melting
is a magma that is
less
mafic than the
parent
rock.
Composition of a rock is ruled by the source area.
Melting mantle
=
mafic magma
melting crust
=
felsic
/
intermediate magma
Magma mixing =
similar viscosities
Magma mingling =
diff viscosities
Grain
size
determines the
cooling speed
of the rock.
Rocks that are
fine-grained
cooled
fast.
Rocks that are
coarse-grained
cooled
slow.
Volcanic
(extrusive) rocks are fine-grained with
aphanitic
texture.
Plutonic (intrusive) rocks are
coarse-grained.
Coarse-grained
=
phaneritic
texture
Extremely coarse pegmatitic
texture
Complex
/
non-uniform
=
porphyritic
holes
=
vesicular
ash
=
pyroclastic
no grains
=
glassy
Welded tuff are formed when particles are
buried
before
cooling down.
Non-welded
tuff (
rhyolitic tuff
) forms when particles cooled before burying.
Plutons are
bodies
of
igneous rocks
which have
intruded
on
country rock