Geology Chapter 4 Magma and Igneous Rocks

Very early in earth's history, it was so hot that the surface was likely entirely molten

True

A dike is a

a sheetlike intrusion that cuts across preexisting layers

If a body of magma becomes for felsic, its viscosity will

increase

A continental volcanic arc occurs at ____________.

Andes Mountains

When rock is melted within Earth, typically the entire volume of rock is transformed from solid state to a liquid.

False

A famous example of hot-spot volcanism occurs at ____________.

Hawaii

Igneous rock

a. are formed through the freezing of a melt b. can be produced at the surface of the earth as well as deep below the surface c. are the most common type of rocks within earth d. all of the above

Obsidian

a. is volcanic glass b. possesses conchoidal fracture c. typically is felsic in composition d. all of the above

Coarse grained diorite is most similar in mineral composition to fine grained a. andesite b. basalt

andesite

Most commonly, felsic igneous rocks

are lighter in color than mafic rocks

Coarse grained gabbro is most similar in mineral composition to fine grained

basalt

Radioactive isotopes, differentiation of Earth's iron core, gravity-driven compression, and meteoric bombardment all caused early earth to

be much hotter than at present

As compared to aphanitic igneous rocks, phaneritic rocks are ____________

coarser grained

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

cool and solidify more quickly

All other factors being equal. intrusive rocks that form deep within earth __ than intrusive rocks that cool near the surface

cool more quickly

If the volatile content of magma is increased, its viscosity will

decrease

Pillow basalts, shown below, attain their distinctive blob-like shapes because their parent lavas do not travel far prior to solidification. This is because the parent lavas ____________.

erupt underwater and thus cool very quickly

Which type of magma has the greatest silica content?

felsic

Volatiles refer to substances that

have a tendency to evaporate and are stable as gases

A volcanic neck, such as that seen at Shiprock, New Mexico (below), is a (an) ____________.

intrusion formed within the magma chamber of a volcano

When magma crystallizes, ____ are formed.

intrusive igneous rocks

Geologically, melts are equivalent to both

lavas and magmas

The formation of magma within earth is not caused by which of the following processes?

loss of volatiles to the atmosphere

A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock. These newly formed magmas are ____________.

mafic

Volcanoes that do NOT occur along either present or emergent plate boundaries are associated with ____________

mantle hot spots

Due to fractional crystallization and assimilation of surrounding host rock, most magmas that rise slowly through the crust evolve chemically to become

more felsic

When rock is partially melted, the chemistry of the melt is

more felsic than the original chemistry of the rock

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

Bowen's continuous reaction series describes the crystallization behavior of a single mineral (with variable chemical composition), ____________.

plagiocase

The silicate mineral that is found in the greatest variety of igneous rocks is ____________

plagiocase

A blob like igneous rock body that has cooled beneath the surface of earth is

pluton

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

Coarse grained granite is most similar in mineral composition to fine grained

rhyolite

As compared to mafic igneous rocks, all felsic igneous rocks

solidify at lower temps

The geotherm is the rate of change of

temp with depth in earth's interior

The difference between magma and lava is

that magma is found beneath the surface, whereas lava is found at the surface

A volcano emits ash, which falls from the sky, settles in layers and is eventually cemented. The resultant rock is termed

tuff

Which type of magma has the greatest iron and magnesium content?

ultramafic

Important volatiles in magmas include ____________.

water and carbon dioxide

Ash and lava fragments that cascade down the sides of a volcano eventually settle and lithify to form

welded tuff