Igneous rock formation Flashcards
2.1-2.4
igneous rocks are formed from
the solidification of a melt
a melt is
molten rock
what’s the difference between lava and magma
magma below ground lava above ground
extrusive is
above ground
intrusive is
below ground
the crust and athenosphere are mostly in what state
solid
melts occur in what areas
localized
the earth has been cooling by
radiating heat out to space
the uppermost layer of the earth froze to form
the crust
how thick is the mantle
2800 km
temp increases or decreases with depth
increases
almost all solid rock is
peridotite
lithosphere thickness
100-150km
lithosphere is the
crust and upper mantle
athenosphere thickness
100-350km
athenosphere is a part of the
mantle
melts occur because of
decrease in pressure (decompression)
introduction of volatiles’ (flux)
heat transfer (heat transfer)
what happens in decompression melting
P decreases but T remains constant
temperature is high enough to melt rock at surface but pressure keeps them solid
how does pressure decrease to allow decompression melting
a volume of hot asthenosphere rises by a mantle plume or divergent plate boundaries
decompression melting creates M/F material
mafic
what kind of melt created hawaii
decompression
what happens in flux melting
volatiles help break chemical bonds, creating a melt
h2o or co2 mi with hot dry rock and help break the chemical bonds
this lowers the melting point of the rock
where does flux melting happen
subduction zones
flux melting creates M/F material
Felsic
Heat transfer melting happens when
heat from magma melts adjacent rocks
hot mantle rises up and brings heat with it
this melts existing crustal rock that has a lower melting point
volcanic ars along plate boundaries come from what type of melting
heat transfer melting
melt composition is defined by
the proportion of different oxides
SILICA SiO2
IRON OXIDE FeO and Fe2O3
MAGNESIUM OXIDE MgO
a dry melt has
no volatiles
a wet melt has
volatiles
What are the four major compositional groups of magma
felsic (silicic). 67-76% silica
intermediate. 53-66% silica
mafic. 46-52% silica
ultramafic. 38-45% silica
felsic magma is what percent silica
67-76%
intermediate magma is what percent silica
53-66%
mafic magma is what percent silica
46-52%
ultramafic magma is what percent silica
38-45%
the four major compositional groups of magma is the percent
magma weight that is silica
the four major compositional groups of solid rock
are dependent on the proportion of silica relative to the combination of magnesium and iron oxide
diorite is _ I/S/M and _ F/M
igneous intermediate
rhyolite I/S/M and F/M
felsic igneous
gabbro I/S/M F/M
igneous mafic
why do melts vary
source rock dictates the initial melt composition
what is magma mixing
different magmas from different source rocks mix in the magma chamber changing the magma composition
what is assimilation / contamination
heat provided by magma partially melts wall rock
the new magma the mixes with the original magma
blocks of wall rock can dissolve in the original magma and that wall rock may chemically react with the magma
changes the melts composition
what is partial melting
only a fraction of a source rock will melt at an achievable P and T
some minerals melt at lower temps than others
in partial melting liquid magma
migrates away from the source rock before the entire rock can melt
partial melting produces a rock with
higher silica content
how does molten rock flow
melts migrate toward the surface due to their relatively low density
viscosity of molten rock depends on
temperature, volatile content, and silica percent content
Low viscosity magma is
Hotter
more mafic
has less volatiles
high viscosity magma is
cooler
more felsic
has more volatiles
mafic melts are ___ viscous than felsic melts. why
less
more silica tetrahedra in felsic magma. they link together and don’t like to flow
how does a melt become a rock
it freezes
migrates towards the surface
loses heat to surrounding rock or erupts onto surface
looses volatiles
the time a melt takes to cool depends on how
well insulated it is
wall rock is a ____insulator than water or air
better
melts cool ___ at the surface than underground
faster
the deeper magma is the hotter
the wall rock will be
a larger intrusion will cool _____ than a small intrusion at the same depth
slower
interaction with ground water can cool a melt _____ as water
faster
as water can carry away heat but also introduce volatiles
thing lava flows cool ____ than thick ones
faster
lava immersed in water cools _____ than water immersed in air
faster
what is fractional crystallization
when a melt cools some minerals form earlier than others due to their melting points
this results in sequential crystal formation
fractional crystallization creates a more
felsic melt
in crystal fractionalization the material that solidifies out is
more mafic
olivine and calcium rich plagioclase
In bowens reaction series Low temperature corresponds to
last minerals to crystallize
felsic materials
in bowens reaction series high the first minerals to crystallize
do so at high temperatures
are ultramafic
What are tabular intrusions
Sills and Dikes
underground solidified melts
Dikes are ___ to rock layers
perpendicular
Sills are ___ to rock layers
parralell
most sills result in a
change in land elevation of the surface
dikes spread in what way
sideways
what is a lacolith
when magma that cannot spread accumulates in a blister shaped intrusion
what is a pluton
a solid igneous intrusion
what is a batholith
a large solid igneous intrusion larger than 100km^2
what is a xenolith
a piece of rock in an igneous rock that is not derived from the original magma that showed up from elsewhere
what is unroofing
when intrusive igneous features are exposed over a long period of time
