Geology Chpt 4

12. Igneous rocks with a texture that is so fine-grained that the crystals are too small to see is ____. a. aphanitic b. porphyritic c. glassy d. phaneritic e. pyroclastic

A

18. ____________________ are concordant, mushroom-shaped plutons.

Laccoliths

13. Natural glass such as obsidian forms when magma does what? a. cools too rapidly for crystals to form b. cools rapidly and very tiny crystals form c. cools too slowly for crystals to form d. doesn't cool e. none of these

A

15. What is a vesicular felsic rock called? a. pumice b. scoria c. obsidian d. tuff e. volcanic breccia

A

8. Although all compositions are represented, most plutons are ____. a. felsic rocks b. intermediate rocks c. mafic rocks d. felsic and mafic rocks e. none of these

A

1. Most plutons form ____. a. well within plates b. at plate boundaries c. without regard to plate boundaries d. above the land surface e. all of these

B

11. Igneous rocks with a two-stage intrusive-extrusive origin are recognized by a texture which is ____. a. aphanitic b. porphyritic c. glassy d. phaneritic e. pyroclastic

B

6. The most widely accepted explanation for chains of volcanoes in the oceans and lines of volcanoes on land is that they formed at ____. a. divergent plate boundaries b. normal faults c. hot spots d. convergent plate boundaries e. transform faults

C

2. Intrusive igneous (plutonic) rocks ____. a. solidify below the surface of the ground b. solidify above the surface of the ground c. form by crystallization of magmas intruded into surrounding rocks d. solidify below the surface AND form by crystallization of intruded magmas e. solidify above the surface AND form by crystallization of intruded magmas

D

3. A dark colored igneous rock with no visible crystals cooled ____. a. slowly in a magma chamber b. quickly in a magma chamber c. slowly on the Earth's surface d. quickly on the Earth's surface e. none of these

D

4. Where are mantle plumes primarily found? a. divergent plate boundaries b. convergent plate boundaries c. transform plate boundaries d. not at plate boundaries e. none of these

D

7. Most igneous rocks are classified by what? a. texture b. composition c. size d. texture and composition e. size and composition

D

10. Large crystals found in a fine-grained groundmass can indicate what? a. origin from a magma with an early intrusive phase followed by an extrusive phase b. origin from a magma with an early extrusive phase followed by an intrusive phase c. a rock of mixed volcanic-plutonic origin d. intrusive slow cooling e. origin from a magma with an early intrusive phase followed by an extrusive phase; a rock of mixed volcanic-plutonic origin

E

14. Igneous rocks formed by explosive volcanic activity have a texture that is termed what? a. aphanitic b. porphyritic c. glassy d. phaneritic e. pyroclastic

E

5. The process of assimilation ____. a. includes melting and incorporation of inclusions b. includes the inclusion of country rock in an intrusive magma c. can explain some of the felsic mineral enrichment of a mafic magma d. results in the cooling of a magma body e. all of these

E

9. Aphanitic, phaneritic, and porphyritic are textural terms that ____. a. refer to fine-grained, course-grained, and mixed grained crystal sizes, respectively. b. refer to formation by slow cooling, fast cooling, and mixed cooling rates, respectively. c. are indicative of volcanic, plutonic, and mixed plutonic-volcanic origins, respectively. d. are fine-grained, coarse grained, and mixed-grained crystal sizes respectively and are indicative of volcanic, plutonic and mixed plutonic-volcanic origins respectively e. all of these

E

1. Any individual volcano always erupts magmas of the same type.

F

4. Geologists agree that hot-spot volcanism results from a rising mantle plume.

F

7. Granite and rhyolite are extrusive and intrusive igneous rocks of the same composition.

F

8. Pegmatites are rocks of felsic composition that are similar to granite.

F

2. ____________________ is the first ferromagnesian mineral to crystallize from a mafic magma.

Olivine

10. Batholiths are emplaced by forceful injection as magma moves upward through country rock.

T

2. Bowen's Reaction Series explains the order of mineral formation with decreasing temperature.

T

3. Bowen's Reaction Series explains why Si-rich minerals are the last to crystallize from a magma.

T

5. The process of assimilation partly explains why felsic intrusive rocks are much more common than mafic intrusive rocks.

T

6. The process of assimilation includes the incorporation of felsic country rock.

T

9. Laccoliths are sills that inflate, causing the overlying rock to bow upward.

T

19. The largest intrusive bodies are called ____________________ and by definition, they must have at least ______ square kilometers of surface area.

batholiths, 100

8. Igneous rocks having a phaneritic texture have ____________________ grains that ____________________ be seen easily by the naked eye.

coarse, can

4. Partial melting of basalt, together with the processes of assimilation, ____________________settling, and ____________________ mixing are believed to explain the generation of felsic intrusive magmas from ____________________ magmas.

crystal, magma, mafic

20. The Columbia Plateau basalts issued from fissures which are now preserved as ____________________.

dikes

15. Andesite and ____________________ are respectively, ____trusive and ____trusive rocks formed in volcanic chains along ____________________ plate boundaries.

diorite, ex-, in-, convergent

7. Rapid cooling of magma results in a(n) ____________________ grained texture called ____________________.

fine, aphanitic

5. The increase in Earth's temperature with depth is called the ____________________.

geothermal gradient

21. Batholiths and stocks can be important sources of minerals such as ____________________ and ____________________.

gold, copper copper, gold

6. According to Bowen's reaction series, crystal settling should result in the magma being separated in lower layers rich in the early-formed ____________________ minerals, and upper layers enriched in later-formed ____________________ minerals.

mafic, felsic

12. Basalt and gabbro are compositional equivalents, which means that they are made up of the same ____________________ but have different ____________________.

minerals, textures

10. An example of a glassy igneous rock is ____________________.

obsidian

14. The ultramafic rock composed predominantly of ____________________ is known as peridotite and is likely the rock that makes up the part of Earth known as the ____________________.

olivine, upper mantle

9. An igneous rock in which large mineral grains called ____________________ are suspended in a finely crystalline groundmass is called a(n) ____________________.

phenocrysts, porphyry

3. The only minerals in the continuous branch of Bowen's reaction series are the ____________________.

plagioclase feldspars

16. Rhyolite and granite are extrusive and intrusive rocks formed by volcanism and ____________________, which form at or near plate boundaries as the result of ____________________ and/or ____________________ of plates.

plutonism, subduction, collision

17. Concordant tabular sheetlike plutons are called ____________________, whereas discordant tabular plutons are called ____________________.

sills, dikes

13. When magma cools slowly, crystal growth proceeds at a relatively ____________________ speed, and the resultant rock is ____________________ in texture.

slow, phaneritic

11. Trapped gases in cooling lava form cavities called ____________________. Cinder cones may contain large amounts of ____________________ which contains more of these cavities than it does rock.

vesicles, scoria

1. The two main categories of igneous rocks are ____________________ and ____________________.

volcanic/extrusive, plutonic/intrusive plutonic/intrusive, volcanic/extrusive