chapter 3

15. Igneous rocks that are silica-rich with high aluminum, sodium, and potassium are _____ rocks. A. silicic B. ultramafic C. mafic D. extraterrestrial E. intermediate

A

24. Crystal settling accounts for important deposits of ______. A. chromium and platinum B. gold C. lead and zinc D. iron E. aluminum and silicon

A

32. What type of melting takes place when a body of hot mantle rock moves upward and the pressure is reducted to the extent that the melting point drops to the temperature of the body? A. decompression melting B. subduction melting C. depressurized melting D. exfoliational melting E. mantle plume melting

A

9. Fine-grained igneous rocks (grains < 1.0 mm) that have small grains cooled rapidly and are likely to be _______. A. extrusive B. reclusive C. intrusive D. obtrusive E. preclusive

A

A ______ is an intrusive structure that formed from magma that solidified within the "throat" of a volcano. A. volcanic neck B. sill C. laccolith D. batholith E. diaper

A

Most of the basalt and gabbro on the ocean floor is created at mid oceanic ridges, which are also ____. A. divergent plate boundaries B. ocean-ocean convergent plate boundaries C. transform plate boundaries D. ocean-continent plate boundaries E. intraplate igneous areas

A

What is the process through which magma differentiation takes place? A. crystal settling B. partial melting C. viscosity of the magma D. heating of the country rock E. subduction

A

13. Both andesite and ___ are composed of feldspars and 30% to 50% ferromagnesian minerals. A. granite B. diorite C. pegmatite D. gabbro E. rhyolite

B

20. ______ is the predominant igneous rock of the continents. A. Basalt B. Granite C. Rhyolite D. Gabbro E. Limestone

B

22. The first plagioclase crystals to form as a hot melt cools are high in ______. A. iron B. calcium C. manganese D. carbonate E. lead

B

31. The huge volume of mafic magma that erupted to form the Columbia plateau basalts of Washington and Oregon are attributed to ___. A. sea floor spreading B. a hot mantle plume C. subduction D. magma mixing E. meteorite impact

B

8. ___ is a coarse-grained igneous rock (grains > 1 mm diameter) with visible grains of quartz. A. Gabbro B. Granite C. Basalt D. Peridotite E. Andesite

B

Imagine two magmas that are identical in all respects (for example, same chemistry, pressure, volume) except that one magma is hotter than the other. Which magma will have the higher viscosity? A. The hotter magma will be more viscous. B. The cooler magma will be more viscous. C. The magmas will have the same viscosity. D. There is not sufficient information to establish the relative viscosities of these magmas. E. Temperature does not affect magma viscosity.

B

The coarse-grained equivalent of basalt is a(n) ______. A. andesite B. gabbro C. granite D. diorite E. rhyolite

B

Viscosity is a property of a fluid that relates to how easily the fluid flows. A material that is viscous __. A. flows easily B. flows less easily C. is always hot D. is always a solid E. is always cold

B

________ lava is largely restricted to narrow zones along convergent plate boundaries. A. Granite B. Andesite C. Rhyolite D. Ultramafic E. Carbonate

B

1. Igneous rocks may be either ____ if they form on or near Earth's surface, or ___ if they solidify under ground. A. intrusive; volcanic B. volcanic; extrusive C. extrusive; intrusive D. plutonic; intrusive E. intrusive; extrusive

C

16. Ultramafic igneous rocks are composed almost entirely of __. A. feldspar B. quartz C. ferromagnesian minerals D. calcite E. diamonds

C

21. The melting point of a mineral generally _____ with increasing pressure (or depth). A. does not change B. decreases C. increases D. becomes dependent on rock type E. is unknown

C

23. Hawaii and __________ eruptions are related to intraplate igneous activity. A. Japan B. Cascade C. Yellowstone D. Honduras E. California

C

25. Geologists regard basaltic magma (Hawaiian lava, for example) as the result of the partial melting of ultramafic rock in the ____. A. oceanic crust B. continental crust C. mantle D. outer core E. inner core

C

5. ______ igneous rocks, like gabbro and basalt, are silica-deficient with high magnesium and iron. A. Felsic/silicic B. Intermediate C. Mafic D. Intrusive E. Extrusive

C

Mafic magma generated in the _______ rises to the base of the crust. A. continental crust B. outer core C. asthenosphere D. spreading ridges E. mantle plumes

C

The most common minerals in a granite are the ______. A. oxides B. carbonates C. feldspars D. ferromagnesians E. micas

C

To explain the great volumes of granite plutonic rocks, most geologists think that partial melting of the _______ must take place. A. core B. lower mantle C. lower continental crust D. oceanic crust E. asthenosphere

C

10. A _______ is a tabular (thin but large area) intrusive body that is concordant (parallel to the host rock structure). A. dike B. mantle C. threshold D. sill E. neck

D

11. ______ are extremely coarse-grained with crystal up to 10 meters across. A. Granites B. Ultramafic C. Basalts D. Pegmatites E. Marbles

D

14. ___ are igneous rocks that are silica-deficient but high in iron and magnesium. A. Felsic B. Intermediate C. Oxide D. Mafic E. Sulfate

D

17. _____, a coarse-grained rock composed of pyroxene and olivine, is the most abundant ultramafic rock. A. Diorite B. Gabbro C. Granite D. Peridotite E. Hematite

D

3. ______ are fragments of country rock that are distinct from the body of igneous rocks in which they are enclosed. A. Clasts B. Chill zones C. Phenocrysts D. Xenoliths E. Necks

D

6. The geothermal gradient, on average, is about _____. A. 0.004C/km B. 2.5C/km C. 25C/km D. 30C/km E. 2500C/km

D

7. Mineralogically and chemically equivalent rocks are ___ and __. A. granite; rhyolite B. gabbro; basalt C. diorite; andesite D. mafic; ultramafic E. intermediate; felsic

D

A useful tool illustrating the relationships among igneous, sedimentary, and metamorphic rocks is called the ___. A. weathering and erosion of surface features B. plate tectonic cycle C. relationships between preexisting rock D. rock cycle E. Bowen's reaction series

D

Granite and ______ are composed predominantly of feldspar and quartz. A. oceanic crust B. diorite C. basalt D. rhyolite E. ultramafics

D

How is a sill different from a dike? A. The sill is tabular in shape. B. Dikes are intrusive structures. C. Dikes are fine-grained and sills are coarse-grained. D. Sills are parallel to the layering in the country rock. E. A sill is shaped like a mattress, while a dike is shaped like a pillow.

D

On its slow journey through the crust, mafic magma evolves into intermediate magma by differentiation and assimilation of ______. A. mantle rocks B. basalt C. gabbro D. silicic rocks

D

The crust beneath the world's oceans is mafic ________. A. iron B. asthenosphere C. granite and rhyolite D. basalt and gabbro E. Answers iron, asthenosphere, and granite and rhyolite are all correct.

D

What is the sequence of crystallization along the discontinuous branch of Bowen's reaction series? A. sodium-rich to calcium-rich plagioclase B. quartz, potassium feldspar, biotite C. silicic, felsic, mafic, intermediate D. olivine, pyroxene, amphibole, biotite E. framework, double chain, single chain, sheet, isolated

D

12. _____ rocks have coarse crystals in a fine-grained matrix. A. Ultramafic B. Granite C. Sill D. Pegmatite E. Porphyritic

E

4. Under ideal conditions rock can melt and yield a granite composition at temperatures as low as ___. A. 100 Celsius B. 225 Celsius C. 333 Celsius D. 450 Celsius E. 650 Celsius

E