5 igneous rocks Flashcards
magma vs lava
Magma: molten rock beneath the Earth’s surface
Lava: molten rock above the Earth’s surface
generation of magma
Magma is formed by melting pre-existing solid rock
Movement of magma is DENSITY-driven
Lava lamps are groovy
And scientific!
Heat source
Geothermal gradient
Deeper you go, hotter you get
Lava lamp light
Cooling area
Earth’s crust
Top of lava lamp
Hot and less dense
Molten Rock
Hot wax near the light
Types of magma melting
Two main types of melting:
Decompression melting
Flux melting (aka dehydration melting)
One subtype
Heat transfer melting
Triggered by either decompression or flux melting
decompression melting
Melting because of pressure reduction
Temperature remains the same
Divergent plate boundaries
Mantle plumes (aka hotspots)
flux/dehydration melting
Flux melting (aka dehydration melting)
Melting due to the addition of water
And CO2
Convergent plate boundaries
With subduction
Continental-oceanic
Oceanic-oceanic
Heat Transfer Melting
Heat transfer melting
Caused by either decompression and flux (dehydration) melting
Surrounding rocks melted by high-heat magma
composition of a melt
Ultramafic melts: Silicates with highest magnesium + iron
Mafic melts: Silicates with high magnesium + iron
Intermediate melts: Silicates with intermediate blend (hence the name)
Felsic melts: Silicates with high silica and alumina
Why is there melt variation
Original source rock
Amount of melting: partial or full
Assimilation of wall rock: graba and melts parts of the wall
silicate mineral groups: felsic
Potassium feldspar
Plagioclase feldspar
Quartz
Muscovite mica
silicate mineral groups: mafic
Olivine
Pyroxene
Amphibole
Plagioclase feldspar
Biotite mica
Viscosity of a Melt
Viscosity = resistance to flow
Melt viscosity
Temperature
Hot = more fluid
Cool = more viscous
Volatiles (dissolved gases)
Higher = more fluid
Lower = more viscous
Composition
Mafic = more fluid
Felsic = more viscous
Intrusive melt
Intrusive: Cooled to solid INSIDE the earth; larger crystals, slower cooling
Plutonic
Extrusive melt
Extrusive: Cooled to solid OUTSIDE the earth; smaller crystals, quicker cooling
Volcanic
Intrusive Rock Bodies
Classification
Based on size, shape, and relationship to the older rocks that surround them
Discordant
Cuts across older rocks
Concordant
Is in line with older rocks
contact metamorphism
Baked rocks around the intrusion
Sills and dikes: properties and differences
Elongate, many times longer than thick
Sills
Concordant
Dikes
Discordant
Laccoliths
Medium sized
“Blister” or tree shaped
Concordant
Examples: Henry Mtns, Abajo Mtns, LaSals, Pine Valley Mtn
plutons
“Blob” shaped frozen magma chambers
Discordant
Examples
Little Cottonwood Stock
ex: Salt Lake Temple Quarry, Little Cottonwood Canyon
batholith
Groups of plutons that cover a large area (domes)
volcanic necks
Leftover, un-erupted magma
Solidifies in volcanic vent
More resistant to erosion
Examples:
Devil’s Tower, Wyoming
Shiprock, New Mexico
location of igneous rocks
Concentrated on recent and former convergent plate margins
Really old intrusive rocks in Canadian Shield
Rarely found on stable platform
Except when mantle plumes strike
ex: iceland is all igneous rocks
Large Igneous Provinces (LIPs)
Large areas of mafic melts
Caused by mantle plumes
Also called “flood basalts”
Classification of igneous rocks: chemical
Felsic vs Mafic
Proportion of felsic minerals to mafic minerals
Felsic minerals (light colored)
Mafic minerals (dark colored)
Classification of gicneous rocks: texture
Crystal size and shape
Coarse grained
Large xls & slow cooling
Fine Grained
Small xls & fast cooling)
Pyroclastic (Fragmented)
broken crystals (explosive eruption)
memorize and draw out igneous classification chart
see screenshot
Glassy texture
Extrusive
No crystals
Cooled before crystals could form
Quick cooling
Typically found
Crust of lava flows
Viscous magma
Think Jolly Rancher
Aphanitic texture
Extrusive
Crystals too small to be seen without a microscope
Rapid cooling
Typically found
Lava flows
Think snickerdoodle
Phaneritic texture
Intrusive
Crystals large enough to be seen by the naked eye
Interlocked together
Slow cooling
Typically found
Intrusive rocks
Think oatmeal cookie
porphyritic texture
Two distinct sizes of crystals
Extruive: Porphyritic aphanitic
Large crystals + microscopic crystals
Two stages of cooling: slow and then fast
Typically found in volcanic rocks
Think chocolate chip cookies
Intrusive: Porphyritic phaneritic
Large crystals + smaller crystals
Two stages of cooling: s-l-o-w-e-r and then slow
Typically found in intrusive rocks
Think oatmeal raisin cookies
Pyroclastic texture
Extrusive
“Broken fire”
Made of crystals (broken), pieces of pumice (broken), rock (broken), and ash (sometimes broken)
Created from explosive volcanic eruptions
Think peanut brittle
use chart to tell differences between pictures of igneous rocks based on color
see screen shots and slide 36-40
