Geology Chapter Igneous rocks

The geothermal gradient, on average, is about ________.

30

If a geologist refers to an igneous rock as plutonic, she means that ________.

Intrusive body of magma

What is the difference between magma and lava?

Lava at rocks surface ; magma molten rocks below earth's surface

Which is not an intrusive igneous rock?

Andesite

What is country rock?

Any rock that was older than and in intruded by an igneous rock

A change in magma composition due to melting of surrounding country rock is called

Assassination

39) The crust beneath the world's oceans is mafic ________.

Basalt and gabbro

The Sierra Nevada range in California is a good example of a granite ________.

Batholith

The difference in texture between intrusive and extrusive rocks is primarily due to

Crystal size intrusive show coarse grained ; Extrusive fine grained

Mafic magma is generated at divergent boundaries because of

Decompression

What type of melting takes place when a body of hot mantle rock moves upward and the pressure is reduced to the extent that the melting point drops to the temperature of the body?

Decompression melting

Most of the basalt and gabbro on the ocean floor is created at mid oceanic ridges, which are also ________.

Divergent plate boundaries

23) Fine-grained igneous rocks (grains < 1.0 mm) that have small grains cooled rapidly and are likely to be ________.

Extrusive

Igneous rocks may be either ________ if they form on or near Earth's surface, or ________ if they solidify underground.

Extrusive; Intrusive

A pluton is an igneous structure that crystallized at very shallow depths.

False

An ultramafic rock is composed almost entirely of quartz.

False

Extrusive igneous rocks are typically fine grained because they crystallized slowly, deep below the Earth's surface.

False

Rhyolite is considerably more common than granite

False

The continuous branch in Bowen's Reaction Series contains the ferromagnesian minerals.

False

The geothermal gradient is the rate at which pressure increases with increasing depth beneath the surface.

False

The melting point of a rock decreases with increasing pressure.

False

The most common minerals in a granite are the ________.

Feldspar

Ultramafic igneous rocks are composed almost entirely of ________.

Ferromagnesian Minerals

The coarse-grained equivalent of basalt is a(n) ________.

Gabbro

________ is a coarse-grained igneous rock (grains > 1 mm diameter) with visible grains of quartz.

Granite

________ is the predominant igneous rock of the continents.

Granite

________ igneous rocks, like gabbro and basalt, are silica-deficient with high magnesium and iron.

Mafic

Mineralogically and chemically equivalent rocks are ________ and ________.

Mafic; Ultramafic

Partial melting of a rock will create a magma that is ________ than the composition of the original rock.

Silicic

________ are extremely coarse-grained with crystal up to 10 meters across.

Pegmatitic

________, a coarse-grained rock composed of pyroxene and olivine, is the most abundant ultramafic rock.

Peridotite

Granite and ________ are composed predominantly of feldspar and quartz.

Rhyolite

18) A useful tool illustrating the relationships among igneous, sedimentary, and metamorphic rocks is called the ________.

Rock Cycle

Considering Bowen's reaction series, a mafic-rich magma will become ________ as it crystallizes

Salizied

Igneous rocks that are silica-rich with high aluminum, sodium, and potassium are ________ rocks.

Silicic

On its slow journey through the crust, mafic magma evolves into intermediate magma by differentiation and assimilation of ________.

Silicic

A ________ is a tabular (thin but large area) intrusive body that is concordant (parallel to the host rock structure).

Sill

How is a sill different from a dike?

Sills are parallel to the layering in the country rock.

By definition, stocks differ from batholiths in

Size

A dike is a discordant intrusive igneous structure.

True

A mineral's melting point generally increases with increasing pressure.

True

Basaltic magmas crystallize at higher temperatures than granitic magmas.

True

Diorite and andesite are composed of similar amounts of feldspars and ferromagnesian minerals.

True

Igneous rock names are based on grain shape and chemical composition.

True

Lava is magma on the Earth's surface.

True

Mafic igneous rocks are silica-poor.

True

Partial melting of the lower continental crust produces a silicic magma that eventually solidifies into granite or rhyolite.

True

The sequence in which minerals crystallize in a cooling igneous melt is called Bowen's Reaction Series.

True

A ________ is an intrusive structure that formed from magma that solidified within the "throat" of a volcano.

Volcanic neck

The major difference between intrusive igneous rocks and extrusive igneous rocks is

Where they solidified

Hawaii and ________ eruptions are related to intraplate igneous activity.

Yellowstone

The melting point of a mineral generally ________ with increasing pressure (or depth).

decreases

The most common igneous rock of the continents is

granite