Question

What properties cause some magmas to be more felsic than others?

Different minerals crystallize at different temperatures, changing the chemistry.

Some parts of the mantle are felsic and some are mafic, creating felsic magma in the crust.

Water from subducting ocean plate mixes with the magma to create felsic magma

Animals change the chemistry of the magma, making it more felsic.

Silica content in igneous rocks controls (select the correct term)

["texture", "viscosity", "crystal size"]         

which, in turn, controls   

["eruption style", "crystal size"]         .

Where would the geothermal gradient be highest? In other words, if you were to drill into the crust, where would the temperature increase the fastest?

in the desert

where water is abundant

under mountain chains

near subduction zones

at mid ocean ridges

What causes melting at mid-ocean ridges?

reducing pressure

removing water

adding pressure

adding water

adding heat

The map shows the plate configurations along the western margin of North America. At which of the locations would we be most likely to find active volcanoes?A. Middle of Juan De Fuca Plate

C. Transform Boundary

B. Western Washington

D. Trench along Oregon Coast

Where does an igneous rock with a fine-grained (aphanitic) texture forms?

on top of the surface

in pegmatitic dikes

deep under the surface

in the middle of a pluton

both deep and shallow depth

A thin intrusion that cuts vertically across layers of sedimentary rocks is a _______.

sill

dike

laccolith

batholith

pluton

Which composition has the least amount of silica?

mafic

felsic

ultramafic

supermediate

intermediate

Where does an igneous rocks with a coarse-grained (phaneritic) texture form?

from a massive ash cloud

on top of the surface

close to the surface but also just below it

on top of the surface after being ejected into the air

deep under the surface

According to Bowen’s Reaction Series (Section 4.2 in your text), as a magma cools, which mineral will crystallize first?

quartz

k-spar

pyroxene

gypsum

olivine

Examine Bowen’s Reaction Series diagram.

If a rock contained amphibole, pyroxene, and olivine, as the rock is heated, which mineral would melt first?

amphibole

pyroxene

olivine

If volatiles such as water vapor and carbon dioxide are added to a rock, what will happen to the melting temperature?

The melting temperature of a rock will increase.

The melting temperature will not change. It is dependent on the pressure.

The melting temperature of a rock will decrease.

What does a P-T diagram show?

How temperature increases but pressure decreases with depth

How Celsius and kilobars change

How pressure and temperature increase with depth

How the mantle is liquid magma under the surface

What creates the small holes found in a vesicular texture?

Burrowing animals

Liquid water

Soluble minerals

Volatiles

Weathering

Peridotite (ultramafic intrusive rock) is the main constituent of which part of the Earth?

Rift zones

Inner core

Magma chambers

Upper mantle

Crust

_______ describes how an entire suite of silicate minerals can form from a single basaltic magma as it cools and crystallizes.

Mohs Hardness Scale

Geologic Rock Cycle

Theory of Plate Tectonics

Bowen's Reaction Series

Gas Law

What was the rate of cooling and the environment of formation of an igneous rock with microscopic (small) crystals?

Fast because it was erupted from a volcano.

Fast because it cooled six miles below the surface.

Slow because the magma was insulated below the surface.

Slow because it cooled in a volcanic lava flow far from the vent.

Which mineral class makes up most igneous rocks?

Halides

Carbonates

Sulfates

Silicates

Sulfides

What kind of volcano is most closely associated with pyroclastic flows?

Composite Cone

Shield

Submersed

Vent

Cinder Cone

What composition(s) of lava are most closely associated with composite cones (stratovolcanoes)?

Gabbro (mafic)

Basalt (mafic)

Andesite and Basalt (intermediate and mafic)

Andesite and Rhyolite (intermediate and felsic)

What kind of viscosity would basalt lava have (compared to rhyolite lava)?

Very high viscosity

High viscosity

Low viscosity

Medium viscosity

Which tectonic setting would produce volcanic arcs of composite cone volcanoes?

Mantle plumes

Divergent boundary

Convergent boundary

Transform boundary

Hot spot

Answer 1

1. What properties cause some magmas to be more felsic than others?

Some parts of the mantle are felsic and some are mafic, creating felsic magma in the crust.

2. Silica content in igneous rocks controls (select the correct term)

"viscosity" which in turn controls "eruption style" [Higher the Si content, higher the viscosity or resistance to flow]

3. Where would the geothermal gradient be highest? In other words, if you were to drill into the crust, where would the temperature increase the fastest?

at mid ocean ridges

4. What causes melting at mid-ocean ridges?

reducing pressure

5. The map shows the plate configurations along the western margin of North America. At which of the locations would we be most likely to find active volcanoes?

D. Trench along Oregon Coast [In this regions volcanoes are due to the convergent plate boundary that produces a subduction zone, trench is a part of subduction one]

6. Where does an igneous rock with a fine-grained (aphanitic) texture forms?

on top of the surface [faster cooling at surface, so crystals do not grow in size]

7. A thin intrusion that cuts vertically across layers of sedimentary rocks is a _______

dike

8. Which composition has the least amount of silica?

ultramafic

9. Where does an igneous rocks with a coarse-grained (phaneritic) texture form?

deep under the surface

10.According to Bowen’s Reaction Series (Section 4.2 in your text), as a magma cools, which mineral will crystallize first?

olivine

11. Examine Bowen’s Reaction Series diagram.

If a rock contained amphibole, pyroxene, and olivine, as the rock is heated, which mineral would melt first?

amphibole

12. If volatiles such as water vapor and carbon dioxide are added to a rock, what will happen to the melting temperature?

The melting temperature of a rock will decrease.

13. What does a P-T diagram show?

How pressure and temperature increase with depth

14. What creates the small holes found in a vesicular texture?

Volatiles

15. Peridotite (ultramafic intrusive rock) is the main constituent of which part of the Earth?

Upper mantle

16. _______ describes how an entire suite of silicate minerals can form from a single basaltic magma as it cools and crystallizes.

Bowen's Reaction Series

17. What was the rate of cooling and the environment of formation of an igneous rock with microscopic (small) crystals?

Fast because it was erupted from a volcano.

18. Which mineral class makes up most igneous rocks?

Silicates

19. What kind of volcano is most closely associated with pyroclastic flows?

Composite Cone

20. What composition(s) of lava are most closely associated with composite cones (stratovolcanoes)?

Andesite and Rhyolite (intermediate and felsic)

21. What kind of viscosity would basalt lava have (compared to rhyolite lava)?

Low viscosity

22. Which tectonic setting would produce volcanic arcs of composite cone volcanoes?

Convergent boundary