Studied by 5 people
Mafic Mineral Conditions
Low SiO2 weight % (50~)
High temp of 1200-1300
With Basalt (Gabbro)
Intermediate Mineral Conditions
Middle SiO2 Weight % (60~)
Mid Temp
With Andesite (Diorite)
Felsic Mineral Conditions
High SiO2 weight % (70~)
Low temp ~600
With Rhyolite (granite)
mafic minerals
olivine
pyroxene
plagioclase
intermediate minerals
quartz
amphibole
pyroxene
plagioclase
felsic minerals
A-feldspar
plagioclase
quartz
biotite
muscovite
What is an igneous rock
rock that crystallizes from melt (based on solidus) and magma
solidus
melting line of the mantle where everything under is solid form.
Higher temp than geotherm typically
geotherm
normal geothermal gradient which is ~ earth temperature.
Slope increases after litho - astheno boundary with increased P
rock-forming tectonic settings
subduction zones
hot spots
midocean ridge
none of these have added heat
Midocean ridge mineral formation
slow seismic velocity
decompression melting
brings rock to surface
decompression melting
heat is constant but the pressure decreases which causes the melt
at MOR and divergent boundaries
Mantle hot spot mineral formation
mantle plumes
hot materials upwell from depth
form of decompression melting
steeper geotherm
hawaii/shield volcanoes
subduction zone mineral formation
addition of water to mantle allows for melt to occur at lower temperature
“wet” solidus of mantle peridotite
from dehydration of hydrous OH in minerals (amphiboles, micas)
how does the addition of water create melt
dehydration of hydrous minerals enters mantle and lowers temperature to melt.
most h2O leaves early if from ocean water
where does the subducting slab go?
Releases water and mantle melt,
“breaks off” and sinks to slab graveyard at boundary
How are igneous rocks classified?
Texture and mineral composition.
ID texture
ID minerals
whats the % of mafic minerals
choose classification diagram (QAP for <90% mafic)
normalize minerals of interest
phaneritic
coarse, can see the grains with naked eye
in intrusive and plutonic setting
Gabbro
aphaneritic
fine graineds, cant see with naked eye
in extrusive and volcanic setting
basalt
Naming of Volcanic rocks
colour as proxy
chemical analysis and diagrams
chemical analysis and calculation of what minerals should be there (CIPW norms)
Field relations at MOR
mafic magma
basalt and gabbro rock
olivine, plagioclase, pyroxene
fine grained basalt forms at
rapid cooling at sea floor
coarse grained gabbro forms at
slower cooling ponds in crust
Landforms at MOR
pillow basalts
sheeted dike complexes
gabbro “kinda like bubbles at the opening”
pillow basalt
underwater lava eruptions
only basaltic
squeeze through the MOR opening
Field associations at Hot Spots
mafic magma
basalt rock
olivine, plagioclase, pyroxene
forms shield volcanoes, yellow stone, hawaii chain, cindercones
landforms at hot spots
flood basalts (erupts on land in water, larger platforms)
columnar basalts (hexagonal)
vesicles
holes from gas bubbles
common in felsic rck
only from volcanic rocks
amygdale
precipitated minerals that filled a vesicle from outside in
rounded blob
quartz or calcite
possibly confused for plag/pyroxene phenocryst
field association for subduction zones
intermediate magma
andesite/diorite rock
plag, pyrox, amphibole, quartz
island arcs
chain of same aged volcanoes at subduction zone at ocean-ocean convergent boundary
strato volcanoes (more silica, some water, more viscous, explosive)
ocean-continental arc
intermediate-felsic magma
andesite, rhyolite, diorite, granite
plag, amphibole, quartz, afeldspar, biotite, muscovite
O-C arc volcanism
higher silica
some water
more viscous
explosive
mafic to felsic rock
hot spot volcanism
low water
50% silica
flows relatively well
quiescent eruptions
basalt
dark, fine grained
plag, pyrox, olivine
phenocrysts of olivine
vesicles/amygdales
escoria
tuff
igneous volcanic ask compacted into rock
phenocrysts common
felsic magma
subduction zones
pyroclastic material
pumice
from volitile magma
more water in it
holy praise be
how do intrusive structures form
melt forms
goes up and melts surroundings
squeezes
cools as it approaches surface and forms a shape
batholith
magma comes to surface but doesnt erupt
sill
a tabular sheet of igneous rock intruded between and parallel with the existing strata
volcanic neck
solidified remains of volcanoes' conduit and plumbing systems that remain after the rest of a volcano has been eroded away
dike
cuts through and fills cracks, typically planar
laccolith
lens-shaped, that has been intruded between rock strata causing uplift in the shape of a dome.
lopolith
reverse of laccolith, dips in rather than domes out
minerals in mantle
olivine, opx, cpx,
aluminous phase, plag, spinel, garnet
perovskite
main lower mantle mineral forms from olivine
octahedral Si
basaltic magma source
upper mantle
granitic magma source
lower crust
xenolith
fragments of wall rock which were formed at greater depths and brought up
peridotite is common one from the mantle
liquidus
line which shows conditions where under the rock is totally liquid
rises with increasing pressure
solidus change depth at 20km
plagioclase-bearing peridotite changes to spinel-bearing peridotite
solidus change at 70 km
spinel-bearing peridotite changes to garnet-bearing peridotite
porphyry
rock containing abundant phenocrysts
latent heat of fusion
an “extra” amount of heat needed to convert a solid rock to liquid. This does not actually heat it, only used for the conversion
how does the latent heat of fusion limit the amount of melting
prevent the temperature from rising too much above the solidus so rocks only partially melt
stock
igneous intrusion with surface exposure of <100km^2
larger form of a batholith
caldera
large kinda circular part of earth that collapsed into a magma chamber
minerals used in IUGD classification of intrusive igneous rocks
Quartz, Alkali feldspar, plagioclase
Note 
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