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 * âwetâ 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,
âbreaks offâ 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 âkinda like bubbles at the openingâ
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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)