Chap 7: Igneous Rock Forming Minerals

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58 Terms

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Mafic Mineral Conditions
Low SiO2 weight % (50\~)

High temp of 1200-1300

With Basalt (Gabbro)
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Intermediate Mineral Conditions
Middle SiO2 Weight % (60\~)

Mid Temp

With Andesite (Diorite)
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Felsic Mineral Conditions
High SiO2 weight % (70\~)

Low temp \~600

With Rhyolite (granite)
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mafic minerals
olivine

pyroxene

plagioclase
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intermediate minerals
quartz

amphibole

pyroxene

plagioclase
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felsic minerals
A-feldspar

plagioclase

quartz

biotite

muscovite
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What is an igneous rock
rock that crystallizes from melt (based on solidus) and magma
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solidus
melting line of the mantle where everything under is solid form.

Higher temp than geotherm typically
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geotherm
normal geothermal gradient which is \~ earth temperature.

Slope increases after litho - astheno boundary with increased P
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rock-forming tectonic settings
* subduction zones
* hot spots
* midocean ridge

none of these have added heat
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Midocean ridge mineral formation
* slow seismic velocity
* decompression melting
* brings rock to surface
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decompression melting
* heat is constant but the pressure decreases which causes the melt
* at MOR and divergent boundaries
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Mantle hot spot mineral formation
* mantle plumes
* hot materials upwell from depth
* form of decompression melting
* steeper geotherm
* hawaii/shield volcanoes
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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)
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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
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where does the subducting slab go?
Releases water and mantle melt,

“breaks off” and sinks to slab graveyard at boundary
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How are igneous rocks classified?
Texture and mineral composition.

* ID texture
* ID minerals
* whats the % of mafic minerals
* choose classification diagram (QAP for
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phaneritic
coarse, can see the grains with naked eye

* in intrusive and plutonic setting
* Gabbro
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aphaneritic
fine graineds, cant see with naked eye

* in extrusive and volcanic setting
* basalt
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Naming of Volcanic rocks
* colour as proxy
* chemical analysis and diagrams
* chemical analysis and calculation of what minerals should be there (CIPW norms)
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Field relations at MOR
* mafic magma
* basalt and gabbro rock
* olivine, plagioclase, pyroxene
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fine grained basalt forms at
rapid cooling at sea floor
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coarse grained gabbro forms at
slower cooling ponds in crust
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Landforms at MOR
* pillow basalts
* sheeted dike complexes
* gabbro “kinda like bubbles at the opening”
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pillow basalt
* underwater lava eruptions
* only basaltic
* squeeze through the MOR opening
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Field associations at Hot Spots
* mafic magma
* basalt rock
* olivine, plagioclase, pyroxene
* forms shield volcanoes, yellow stone, hawaii chain, cindercones
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landforms at hot spots
* flood basalts (erupts on land in water, larger platforms)
* columnar basalts (hexagonal)
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vesicles
* holes from gas bubbles
* common in felsic rck
* only from volcanic rocks
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amygdale
* precipitated minerals that filled a vesicle from outside in
* rounded blob
* quartz or calcite
* possibly confused for plag/pyroxene phenocryst
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field association for subduction zones
* intermediate magma
* andesite/diorite rock
* plag, pyrox, amphibole, quartz
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island arcs
chain of same aged volcanoes at subduction zone at ocean-ocean convergent boundary

* strato volcanoes (more silica, some water, more viscous, explosive)
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ocean-continental arc
* intermediate-felsic magma
* andesite, rhyolite, diorite, granite
* plag, amphibole, quartz, afeldspar, biotite, muscovite
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O-C arc volcanism
* higher silica
* some water
* more viscous
* explosive
* mafic to felsic rock
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hot spot volcanism
* low water
* 50% silica
* flows relatively well
* quiescent eruptions
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basalt
* dark, fine grained
* plag, pyrox, olivine
* phenocrysts of olivine
* vesicles/amygdales
* escoria
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tuff
* igneous volcanic ask compacted into rock
* phenocrysts common
* felsic magma
* subduction zones
* pyroclastic material
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pumice
* from volitile magma
* more water in it
* holy praise be
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how do intrusive structures form
* melt forms
* goes up and melts surroundings
* squeezes
* cools as it approaches surface and forms a shape
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batholith
magma comes to surface but doesnt erupt
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sill
a __tabular__ sheet of __igneous__ rock __intruded__ between and parallel with the existing strata
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volcanic neck
solidified remains of volcanoes' conduit and plumbing systems that remain after the rest of a volcano has been eroded away
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dike
cuts through and fills cracks, typically planar
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laccolith
lens-shaped, that has been __intruded__ between rock strata causing __uplift__ in the shape of a dome.
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lopolith
reverse of laccolith, dips in rather than domes out
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minerals in mantle
olivine, opx, cpx,

aluminous phase, plag, spinel, garnet
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perovskite
main lower mantle mineral forms from olivine

octahedral Si
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basaltic magma source
upper mantle
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granitic magma source
lower crust
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xenolith
fragments of wall rock which were formed at greater depths and brought up

peridotite is common one from the mantle
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liquidus
line which shows conditions where under the rock is totally liquid

rises with increasing pressure
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solidus change depth at 20km
plagioclase-bearing peridotite changes to spinel-bearing peridotite
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solidus change at 70 km
spinel-bearing peridotite changes to garnet-bearing peridotite
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porphyry
rock containing abundant phenocrysts
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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
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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
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stock
igneous intrusion with surface exposure of
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caldera
large kinda circular part of earth that collapsed into a magma chamber
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minerals used in IUGD classification of intrusive igneous rocks
Quartz, Alkali feldspar, plagioclase