91 terms

Minerals Pt. 3 (Magma)

Magma and lava are __________ material
How to melt rock?
temperature + pressure
If temp increases enough, rocks will melt but....
not a lot of melts, just a percent or two
What does temperature of rock explain? But does it do a poor job of explaining?
formation of plutonic (intrusive) rocks; volcanoes
Increasing the pressure...
increases the melting temperature
If you can lower the pressure + keep temp the same...
you can induce melting
Adding ___________ lowers the melting temperature
What happens to water at a subduction zone?
water is brought down by subducting plate
What does water at subduction zones help create?
As magma rises, pressure is reduced, which causes what?
water to escape from magma
Water escaping will cause...
2 Main Igneous rock textures...
coarse, phaneritic + fine, aphanitic
3 Main Igneous rock compositions...
felsic, intermediate, mafic
Once we determine texture + composition...
we name igneous rocks
rock names imply both...
texture + composition
Temperature of magma is related to the...
elements/minerals present
resistance to flow
High viscosity?
high resistance to flow (hard for it to flow)
Low viscosity?
low resistance to flow (easy for it to flow)
Volatile content in magma?
H20, dissolved gases, other fluids
Mafic/Basaltic magma temp?
Mafic/Basaltic silica content?
M/B volatile content?
M/B viscosity?
Likelihood of M/B reaching the surface?
high: likely to make volcanic rocks
Felsic/Granitic magma temp?
Felsic/Granitic magma silica content?
F/G volatile content?
F/G viscosity?
F/G likelihood of reaching the surface?
low, likely to make plutonic rocks
What is the most common tectonic setting that mafic/basaltic magmas form?
mid-ocean ridges (divergence between 2 oceanic crusts) + hot spots in oceanic crust
Why is magma M/B at mid-ocean ridges?
b/c the source of the magma is the mantle, which is mafic-ultramafic in composition
Are only mafic rocks (basalt, gabbro, diorite) found at these places?
No, but mafic rocks are the majority
3 processes help make magmas more felsic...
fractional crystallization, assimilation, + magma mixing
Volcanoes at subduction zones are mostly...
intermediate rocks
Fractional crystallization...
as mafic magma cools, minerals crystallize at different times
minerals that crystallize first tend to...
settle out of the magma
resulting magma, after fractional crystallization...
is more felsic in composition
as magma rises, it can melt surrounding rock
Adding these melted minerals will result in a a more __________ magma
2 most common types of rock found at subduction zone volcanoes?
andesite + diorite
andesite + diorite are __________ ________/________ types
intermediate magma/rock
2 other minerals found at subduction zone volcanoes?
basalt + rhyolite
Assimilation can occur at/around __________ as magma rises
subduction zone volcanoes
Eruption style of M/B magmas?
Mafic lavas make....
shield volcanoes
Examples of shield volcanoes...
Hawaii + hotspots in oceanic crust
Characteristics of Hawaii - shield volcano
broad, low angle slopes

eruption style is effusive, not explosive
Eruption style of F/G magmas?
Intermediate + Felsic lavas make...
stratovolcanoes or composite cones
3 Properties of stratovolcanoes?
higher angle slopes;
more explosive eruptions;
range of lava compositions
stratovolcano lava?
mostly intermediate, but some mafic + felsic too
Magma mixing?
as plate is subducted, more magma is generated

younger magmas mix w/ older magmas to change composition
the type of magma/lava determines: (4)
what is erupted;
style of eruption;
frequency of eruption;
Volcanic ejecta?
materials that comes out of volcanoes
basaltic, andesitic, rhyolitic
Pyroclastic material, tephra
explosive material defined by size: bombs, cinders, ash
Other volcanic ejecta?
mudflow: lahars
Fire fragments =
4 properties of pyroclastics
blown out;
usually felsic -> intermediate
glass fragments
forms layers
3 Different fire fragments?
ash, cinders, bombs
Pryoclastic flow....example?
flowing cloud of hot ash + cinders;
eventually becomes welded tuff

volcanic mudflow
How do lahars form?
in a variety of ways; need water, dirt + slope
Lahars are not always related to...
Example of lahar?
Mt. St. Helens
What determines the style of eruption a volcano will have?
type of lava is very important
Lava varies in...
temperature, viscosity, volatile content
Effusive eruption:
runny, low viscosity lava
Explosive eruption:
sticky, high viscosity lava
Forming calderas (4 step cycle)
1. Bulge in surface created by magma chamber
2. Crust thinned over magma chamber (ground surface cracks in ringlike fractures)
3. Tephra columns erupt from fractures + collapse into ash and pumice flows
4. surface crust collapses as magma is depleted forming caldera
Calderas, like Yellowstone, experience...
vertical changes in ground level
Flood/Plateau Basalt; example?
...the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava

Columbia River
Intrusive igneous landforms...
volanco, sill, laccolith, batholith, dike, diatreme
large intrusive igneous bodies
really big plutons
Example of plutons/batholiths?
Sierra Nevada Mtns (Giant granitic plutons)
Chill dog you got this...
true that
Economic importance of igneous rocks
metals; igneous activity is a conduit for more dense material to move from the mantle to the crust
Many metals + minerals are associated with...
igneous activity/bodies
Other types of volcanoes?
Calderas, Flood Basalts (Plateau basalts)
What are flood basalts?
massive basalt flows on the continents
What is the cause/tectonic setting of flood basalts?
unknown; none active today, but many ancient ones
Columbia River flood basalts
more than 300 individual lava flows
large bodies of magma that cooled underground (may be related to magma chambers)
large plutons
thin intrusion of igneous rock parallel to rock layers
thin intrusion of igneous rock, cuts across rock layers
Volcanic neck
vertical section of igneous rock w/ sills and/or dikes radiating from it;
thought to be an old magma chamber feeding a volcano
Examples of plutons/batholiths
Mt. Rushmore, Half Dome