Chap 7: Igneous Rock Forming Minerals

Low SiO2 weight % (50~)

High temp of 1200-1300

With Basalt (Gabbro)

Middle SiO2 Weight % (60~)

Mid Temp

With Andesite (Diorite)

High SiO2 weight % (70~)

Low temp ~600

With Rhyolite (granite)

olivine

pyroxene

plagioclase

quartz

amphibole

pyroxene

plagioclase

A-feldspar

plagioclase

quartz

biotite

muscovite

rock that crystallizes from melt (based on solidus) and magma

melting line of the mantle where everything under is solid form.

Higher temp than geotherm typically

normal geothermal gradient which is ~ earth temperature.

Slope increases after litho - astheno boundary with increased P

• subduction zones

• hot spots

• midocean ridge

none of these have added heat

• slow seismic velocity

• decompression melting

• brings rock to surface

• heat is constant but the pressure decreases which causes the melt

• at MOR and divergent boundaries

• mantle plumes

• hot materials upwell from depth

• form of decompression melting

• steeper geotherm

• hawaii/shield volcanoes

• 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)

• dehydration of hydrous minerals enters mantle and lowers temperature to melt.

• most h2O leaves early if from ocean water

Releases water and mantle melt,

“breaks off” and sinks to slab graveyard at boundary

Texture and mineral composition.

• ID texture

• ID minerals

• whats the % of mafic minerals

• choose classification diagram (QAP for <90% mafic)

• normalize minerals of interest

coarse, can see the grains with naked eye

• in intrusive and plutonic setting

• Gabbro

fine graineds, cant see with naked eye

• in extrusive and volcanic setting

• basalt

• colour as proxy

• chemical analysis and diagrams

• chemical analysis and calculation of what minerals should be there (CIPW norms)

• mafic magma

• basalt and gabbro rock

• olivine, plagioclase, pyroxene

rapid cooling at sea floor

slower cooling ponds in crust

• pillow basalts

• sheeted dike complexes

• gabbro “kinda like bubbles at the opening”

• underwater lava eruptions

• only basaltic

• squeeze through the MOR opening

• mafic magma

• basalt rock

• olivine, plagioclase, pyroxene

• forms shield volcanoes, yellow stone, hawaii chain, cindercones

• flood basalts (erupts on land in water, larger platforms)

• columnar basalts (hexagonal)

• holes from gas bubbles

• common in felsic rck

• only from volcanic rocks

• precipitated minerals that filled a vesicle from outside in

• rounded blob

• quartz or calcite

• possibly confused for plag/pyroxene phenocryst

• intermediate magma

• andesite/diorite rock

• plag, pyrox, amphibole, quartz

chain of same aged volcanoes at subduction zone at ocean-ocean convergent boundary

• strato volcanoes (more silica, some water, more viscous, explosive)

• intermediate-felsic magma

• andesite, rhyolite, diorite, granite

• plag, amphibole, quartz, afeldspar, biotite, muscovite

• higher silica

• some water

• more viscous

• explosive

• mafic to felsic rock

• low water

• 50% silica

• flows relatively well

• quiescent eruptions

• dark, fine grained

• plag, pyrox, olivine

• phenocrysts of olivine

• vesicles/amygdales

• escoria

• igneous volcanic ask compacted into rock

• phenocrysts common

• felsic magma

• subduction zones

• pyroclastic material

• from volitile magma

• more water in it

• holy praise be

• melt forms

• goes up and melts surroundings

• squeezes

• cools as it approaches surface and forms a shape

magma comes to surface but doesnt erupt

a tabular sheet of igneous rock intruded between and parallel with the existing strata

solidified remains of volcanoes' conduit and plumbing systems that remain after the rest of a volcano has been eroded away

cuts through and fills cracks, typically planar

lens-shaped, that has been intruded between rock strata causing uplift in the shape of a dome.

reverse of laccolith, dips in rather than domes out

olivine, opx, cpx,

aluminous phase, plag, spinel, garnet

main lower mantle mineral forms from olivine

octahedral Si

upper mantle

lower crust

fragments of wall rock which were formed at greater depths and brought up

peridotite is common one from the mantle

line which shows conditions where under the rock is totally liquid

rises with increasing pressure

plagioclase-bearing peridotite changes to spinel-bearing peridotite

spinel-bearing peridotite changes to garnet-bearing peridotite

rock containing abundant phenocrysts

an “extra” amount of heat needed to convert a solid rock to liquid. This does not actually heat it, only used for the conversion

prevent the temperature from rising too much above the solidus so rocks only partially melt

igneous intrusion with surface exposure of <100km^2

larger form of a batholith

large kinda circular part of earth that collapsed into a magma chamber

Quartz, Alkali feldspar, plagioclase