Igneous Rocks Flashcards
What is the difference between magma and lava?
Both are hot liquid rock with crystals, fragments of rock, and gas, but lava exists at the surface of the earth, while magma resides below.
Three ways to melt a rock
Raise Temp, lower pressure, move the phase boundary
What three main locations generate magma and igneous rocks?
hotspots, spreading ridges, and subduction zones
How do spreading ridges melt rock?
They increase temperature and significantly decrease the pressure. (decompression melting)
How do subduction zones melt rock?
The presence of water shifts the melting point of rock down, and partial melting can occur at lower temperatures (flux melting)
lava that crystallizes form what kind of rocks?
extrusive rocks (volcanic)
Magma that crystallizes before reaching the surface forms what kind of rocks?
intrusive (plutonic)
How are igneous rocks classified?
texture (grain size) and chemical composition
What is the texture of volcanic rocks?
Fine grained to glassy
What is the texture of plutonic rocks
coarse grained (slow cooling)
Give an example of ultramaific material
mantle (low in silica)
Give an example of mafic material
basalt, oceanic crust
Give an example of felsic material?
granite, high in silica
What is Bowens Reaction Series?
Minerals crystalize and settle out of magma in a definite sequence, starting with olivine and certain feldspars, and ends with quartz. RULE: mafic materials crystalize first, felsic materials crystalize last.
Define viscosity
resistance to flow
What has higher viscosity, felsic or maific magma?
felsic (more silicates)
What defines mafic lava flow? (3)
- large, lower viscoisty flows. 2. less explosive eruptions. 3. low ratio of pyroclastic sediment to lava
What defines felsic lava flow? (3)
- smaller, higher viscosity lava flows. 2. explosive eruptions. (since lava is thick and can build a lot of pressure before finally erupting) 3. High ratio of pyroclastic sediment to lava
Define pyroclastic sediment
broken up particles of rocks and minerals deposited during volanic eruption
What makes shield volcanoes
The low viscosity of mafic magma
What makes stratovolcano
felsic, high viscosity of lava
what kind of magma does a mid-oceanic ridge produce>?
maific magma, since there is little fractionation
What is fractionation?
time spent in magma chamber, so the longer you are there, the more minerals that can crystalize out
What kind of magma is made by island arc volcanoes?
mafic to intermediate magma produced
what kind of lava is produced in continental margin volcanoes?
maific to felsic magma
what kind of magma is produced by hotspots?
mafic (oceanic ones) to mafic and felsic magma (continental hotspots)
Many igneous rocks crystallize at great depth in the Earth’s crust.
How is it possible that these rocks are exposed at the Earth’s surface
today?
Tectonic uplift and erosion
. Lava generates
a) igneous rock with small crystals.
b) stratovolcanoes, not shield volcanoes.
c) most granite in the crust.
d) None of the above.
a
Flux melting generates magma at
a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above
a
Decompression melting generates magma at
a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above.
b
Partial melting generates magma at
a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above.
d
Crystallization in a cooling magma
a) proceeds according to Bowen’s reaction series.
b) commonly causes the magma to become more felsic over time.
c) can explain compositional differences between some igneous rocks.
d) All of the above.
d
The viscosity of a magma increases with
a) decreasing silica content.
b) increasing volatile content.
c) increasing temperature.
d) None of the above
d
Relative to felsic magmas, mafic magmas tend to be associated with
a) larger, lower-relief volcanoes.
b) a less-explosive style of volcanism.
c) volcanoes with a lower ratio of pyroclastic sediment to lava.
d) All of the above.
d
Sedimentary rocks cover ~75% of Earth’s surface, but only account for
~10% of the weight of the crust because…
a) they can be converted to igneous rocks at depth.
b) they form at the Earth’s surface.
c) they can be converted to metamorphic rocks at depth.
d) All of the above
d
