GEOL EXAM pt2ch6

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A pegmatite is a course-grained igneous rock that forms primarily because the melt

is water-rich.

because of its physical properties, magma tends to

move upward, away from where it formed

igneous rocks are formed by

through the freezing or crystallization of a melt

Compare and contrast a dike and a sill. How do they relate to surrounding rock layers?

Dikes and sills are both tabular igneous intrusions. Dikes cut across preexisting layering (bedding or foliation), whereas sills intrude parallel to preexisting layering. Dikes are vertically oriented tabular intrusions, whereas sills are near horizontally oriented.

List the four major magma compositions in order of silica content. (highest -> lowest)

Felsic Intermediate Mafic Ultramafic

If you find a tuff in the field, what type of geologic activity could you reasonably assume has occurred?

a volcanic eruption

most commonly, felsic igneous rocks

are lighter in color than mafic rocks

a vast, composite intrusive igneous body that covers hundreds of square kilometers is called

batholith

differentiation of the earth's iron core and collisions of planetesimals caused early earth to

be much hotter than at present

As compared to aphanitic igneous rocks, phaneritic rocks are

coarser grained.

A volcanic arc results from __________ tectonic movements and is associated with a __________.

convergent; subduction zone

As compared to coarse-grained igneous rocks, fine-grained igneous rocks

cool and solidify more quickly

Vesicles in an igneous rock are evidence for which of the following?

degassing of volatiles

In the figure, what type of intrusion is the VERTICAL rock unit shown

dike

volatiles refers to substances that

evaporate easily and exist as gases

which type of magma has the greatest silica content

felsic

as compared to mafic igneous rocks, felsic igneous rocks

have a higher proportion of silica relative to Mg oxide and Fe oxide

Shiprock, New Mexico, is an

intrusion that represents the eroded remnant of an extinct volcano

when magma solidifies below the surface of the earth, are formed

intrusive igneous rocks

which of the following processes is not responsive for the formation of magma within the earth

loss of volatiles to the atmosphere

the difference between magma and lava is

magma is melt underground, whereas lava is melt that has emerged from the surface

in general, when rock is partially melted, the chemistry if the melt is

more felsic than the original chemistry of the rock that was partially melted

in general, if a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be

more felsic than the source rock

During fractional crystallization of a magma body, the first rock that is expected to crystallize from the magma will be

more mafic than the magma

in the discontinuous series of Bowen's reaction series, the first mineral to crystallize from a mafic melt is

olivine

the continuous series in Bowen's Reaction series describes the crystallization of which mineral

plagioclase

An igneous rock with a mixed texture consisting of coarse crystals (phenocrysts) surrounded by fine crystals (groundmass) is termed

porphyritic

Pegmatites, which often 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

Granite, an intrusive igneous rock, is most similar in mineral composition to which extrusive equivalent?

rhyolite

in the figure, what type of igneous intrusion is the HORIZONTAL rock unit shown

sill

A magma body with a ________ volume and a ________ shape cools fastest.

smaller; pancake

Flood basalts such as those found in the Columbia Plateau and the Deccan region are associated with

superplumes.

Which of the following does not affect the cooling rate of magma?

tectonic setting

Fragments of material erupted from a volcano eventually settle and lithify to form an extrusive igneous rock called

tuff


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