Geol Test 2 (26-52)
Why are igneous rocks important?
They provide information about the mantle. They can be used to reconstruct tectonic activity. They host important mineral deposits.
Why are intrusive igneous rocks exposed today?
Wind, water, and ice erode overlying rock to expose igneous rocks
If a body of magma becomes more felsic, its viscosity will
increase
Why don't all igneous rocks contain all the minerals listed in Bowen's Reaction Series?
Crystallization may be complete before all of the minerals in the series have had time to form.
As compared to coarse-grained igneous rocks, all fine-grained igneous rocks
cool and solidify more quickly
Which of the following is NOT a factor controlling the cooling rate of magm
depth of intrusion, presence of circulating groundwater, shape and size of magma body
Consult the figure below. If you found deposits of tuff at an ___________ igneous setting, you could conclude that the lava had a ___________ viscosity content
extrusive; high
Without igneous rocks, which of the following would not be significantly different on our planet?
formation of deserts
A volcanic neck, such as that seen at Shiprock, New Mexico (below), is a(n) ____________.
intrusion formed within a volcano
Obsidian:
is volcanic glass c. typically is felsic in composition b. possesses conchoidal fracture
As compared to aphanitic igneous rocks, phaneritic rocks are
made of crystals big enough to see
Due to fractional crystallization and assimilation of surrounding host rock, most magmas that rise slowly through the crust chemically evolve to become
more felsic
If a body of magma is subjected to fractional crystallization, the rock that results is expected to be
more mafic than the magma
In Bowen's discontinuous reaction series, the first mineral to crystallize from a mafic melt is
olivine
Stoping by magmas occurs when ____________.
pieces of surrounding country rock are broken off and assimilated
The silicate mineral that is found in the greatest variety of igneous rocks is ____________.
plagioclase
A blob-like igneous rock body that has cooled beneath the surface of Earth is
pluton (pluto is a blob in the sky)
An igneous rock with a mixed texture of coarse grains (phenocrysts) surrounded by fine crystals (groundmass) is termed
porphyritic
Pegmatites, which occur in dikes, are unusual among shallow intrusive rocks in that they
possess exceptionally coarse grains
Bombs, ash, and cinders are all examples of
pyroclastic debris
a dike is a
sheet-like intrusion that cuts across preexisting layers
Consult the figure below. A sill is a(n)____________.
sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock
Viscosity depends on
silica content, temperature, volatile content
In regard to the cooling of molten rock, a __________ volume and a __________ shape cools faster
smaller; pancake
If you determine the composition of an igneous rock, you can deduce a number of things about the rock's origin. Which one of these is NOT one of those things
the exact age of the rock
A famous example of hot-spot volcanism occurs at ____________.
the island of Hawaii