Geol HW 2

*Mount St. Helens and the other Cascade volcanoes are ________. Select one: a. young, active volcanoes built on a continental margin above a sinking slab of oceanic lithosphere b. a row of young, active, volcanoes built as western North America moved over a hot spot deep in the mantle c. old, deeply eroded volcanoes built before the Pacific Ocean existed d. old, deeply eroded, basaltic volcanoes built when western North America was over the present-day site of the Hawaiian hot spot

A

*Which of the following statements apply to the asthenosphere, but not the lithosphere? Select one: a. zone in the upper mantle that deforms by plastic flowage b. cool, rigid layer of crust and upper mantle that forms the tectonic plates c. deforms mainly by brittle fracturing and faulting d. partial melting of rising granitic plumes produces huge volumes of basaltic magma

A

All of the following contribute evidence supporting the theory of plate tectonics except for ________. Select one: a. changes in the Moon's orbit due to shifting plates b. ocean floor drilling c. hot spots d. measurements of plate motions

A

Which of the following best describes an aphanitic texture? Select one: a. The rock is crystalline; mineral grains are too small to be visible without a magnifying lens or microscope. b. The mineral grains have glassy textures. c. The rock consists of broken, volcanic-rock and mineral fragments. d. The rock is crystalline; mineral grains are of distinctly different sizes.

A

Which of the following igneous rocks has a pyroclastic texture? Select one: a. rhyolitic tuff b. porphyritic basalt c. intrusive granite d. andesitic lava

A

New oceanic crust and lithosphere are formed at ________. Select one: a. convergent boundaries by submarine eruptions and intrusions of basaltic magma b. divergent boundaries by submarine eruptions and intrusions of basaltic magma c. divergent boundaries by submarine eruptions and intrusions of rhyolitic magma d. convergent boundaries by submarine eruptions and intrusions of rhyolitic magma

B

The sizes, shapes, and arrangements of mineral grains in an igneous rock is known as ________. Select one: a. silica content b. texture c. mineral content d. Bowen's reaction series

B

Where would you drill to recover samples of the oldest basalts of the oceanic crust, which are Jurassic in age? Select one: a. crest of the East Pacific, mid-ocean ridge b. oceanic side of the Aleutian trench , along the southern coastline of Alaska c. just offshore from the Hawaiian Islands d. Mid-Atlantic Ridge under Iceland

B

Which of the following minerals crystallize early in Bowen's reaction series? Select one: a. muscovite b. olivine c. quartz d. biotite

B

Which of the following paleoclimatic evidence supports the idea of the late Paleozoic super continent in the Southern Hemisphere? Select one: a. lithified loess (wind-blown) deposits in the deserts of Chile, Australia, and Africa b. tillites (rocks formed by glaciers) in South Africa and South America c. thick sediments in the Amazon and Congo deltas of South America and Africa d. cold water fossils in the deep-water sediments of the South Atlantic abyssal plain

B

Why is so much basaltic magma erupted along mid-ocean ridges? Select one: a. Basaltic mantle under the ridge is hot enough to completely melt if seawater is added. b. Lowered pressures decrease the temperatures at which a rising plume of mantle peridotite can partially melt and form basaltic magma. c. The subducting, oceanic slab sinks so deep that eventually it melts, producing massive quantities of basalt magma. d. The mantle beneath the ridges is enriched in thorium, uranium, and potassium, causing strong heating due to energy from radioactive decay.

B

________ most effectively outline the edges of the lithospheric plates. Select one: a. The locations of deep mantle hot spots b. Lines of earthquake epicenters c. Lines of active stratovolcanoes d. Margins of the continental shelves

B

________ was never proposed as evidence supporting the existence of Pangaea. Select one: a. Geometrical fit between South America and Africa b. Islands along the Mid-Atlantic Ridge with rocks dating back from 542 million to 2500 million years ago c. Late Paleozoic glacial features d. The Glossopteris flora

B

Cooler, older, oceanic lithosphere sink into the mantle at ________. Select one: a. transform fault zones along divergent plate boundaries b. sites of long-lived, hot spot volcanism in the ocean basins c. subduction zones along convergent plate boundaries d. rift zones along mid-ocean ridges

C

Deep ocean trenches are surficial evidence for ________. Select one: a. rifting beneath a continental plate and the beginning of continental drift b. rising of hot asthenosphere from deep in the mantle c. sinking of oceanic lithosphere into the mantle at a subduction zone d. transform faulting between an oceanic plate and a continental plate

C

In the early part of the 20th century, ________ argued forcefully for continental drift. Select one: a. Karl Wagner b. Peter Rommel c. Alfred Wegener d. Bill Kohl

C

Linear, magnetic patterns associated with mid-ocean ridges are configured as ________. Select one: a. concentric circles about a rising plume of hot, mantle rocks and magma b. reversed magnetizations along the rift valleys and normal magnetizations along the ridge c. normal and reversed magnetized strips roughly parallel to the ridge d. normal and reversed magnetized strips roughly perpendicular to the ridge axis

C

New oceanic crust and lithosphere are formed at ________. Select one: a. divergent boundaries by submarine eruptions and intrusions of rhyolitic magma b. convergent boundaries by submarine eruptions and intrusions of rhyolitic magma c. divergent boundaries by submarine eruptions and intrusions of basaltic magma d. convergent boundaries by submarine eruptions and intrusions of basaltic magma

C

On the average, lithospheric plates are ________ thick. Select one: a. l km b. 10 km c. l00 km d. 1000 km

C

The former, late Paleozoic super continent is known as ________. Select one: a. Pandomonia b. Pancakea c. Pangaea d. Panatopia

C

________ is the dominant feldspar in basalt. Select one: a. Microcline b. Orthoclase c. Plagioclase d. Pyroxene

C

________ was a flora that was widely distributed throughout the once contiguous, late Paleozoic, Southern Hemisphere landmass. Select one: a. Granopteris b. Monastarious c. Glossopteris d. Mesosaurus

C

*The term for the pattern developed by cooling Igneous intrusions as they shrink and crack such as in a sill or dike is called

Columnar jointing

*What type of plate boundary is the Andes Mountains

Convergent Ocean-Continent

A ________ texture would be most unlikely to occur in an extrusive igneous rock. Select one: a. pyroclastic b. glassy c. aphanitic d. phaneritic

D

A transform plate boundary is characterized by ________. Select one: a. stratovolcanoes on the edge of a plate and shield volcanoes on the adjacent plate b. two, converging, oceanic plates meeting head-on and piling up into a mid-ocean ridge c. a divergent boundary where the continental plate changes to an oceanic plate d. a deep, vertical fault along which two plates slide past one another in opposite directions

D

A typical rate of seafloor spreading in the Atlantic Ocean is ________. Select one: a. 2 feet per year b. 0.1 inches per year c. 20 feet per year d. 2 centimeters per year

D

All of the following are factors that affect the generation of magma except for ________. Select one: a. volatiles b. pressure c. heat d. crystal size

D

Changing the composition of magma by incorporating surrounding host rock is known as ________. Select one: a. magma mixing b. partial melting c. differentiation d. assimilation

D

Deep-focus earthquakes are associated with ________ plate boundaries. Select one: a. lateral b. divergent c. transform d. convergent (subducting)

D

Deep-oceanic trenches are most abundant around the rim of the ________ ocean basin. Select one: a. Atlantic b. Indian c. Arctic d. Pacific

D

The Aleutian Islands occur at a ________. Select one: a. transform boundary where North America has moved towards Alaska b. convergent, continental margin with uplifted fault blocks, much like those of the Basin and Range Province c. divergent boundary where shield volcanoes are forming d. convergent boundary on a volcanic arc above a northward-subducting Pacific plate

D

The ________ is (are) a logical evolutionary analog of the African Rift Valleys ten million years from now. Select one: a. Ural Mountains b. San Andreas fault c. Peru-Chile trench d. Red Sea

D

The temperature below which magnetic material can retain a permanent magnetization is called the ________. Select one: a. Darcy temperature b. Vine temperature c. Bullard point d. Curie point

D

Which igneous rock or magma has the lowest silica (SiO2) content? Select one: a. granite b. basalt c. andesite d. peridotite

D

Which of the following energy sources is thought to drive the lateral motions of Earth's lithospheric plates? Select one: a. electrical and magnetic fields localized in the inner core b. swirling movements of the molten iron particles in the outer core c. gravitational attractive forces of the Sun and Moon d. export of heat from deep in the mantle to the top of the asthenosphere

D

________ has the same mineral composition as andesite. Select one: a. Basalt b. Granite c. Gabbro d. Diorite

D

*The Red Sea is an example of which type of boundary

Divergent

T/F A porphyritic texture includes two different sizes of mineral grains, the phenocrysts and the vesicles.

False

T/F As the South Atlantic basin widens by seafloor spreading, Africa and South America are moving closer together.

False

T/F Iceland is a good example of an island arc, formed from an oceanic-oceanic plate collision.

False

T/F Pegmatites are smaller volume, intrusive bodies with glassy textures.

False

The last minerals to crystallize on Bowen's Reaction Series result in igneous rocks with a ________ composition.

Felsic

*A very long-lived magma source located deep in the mantle is called a ________.

Hot Spot

*Lava erupting on the sea floor may form rounded balls of rock that we refer to as

Pillow Lava

*Which two minerals define a felsic composition?

Quartz and Potassium Felspar

T/F Basalt is the aphanitic or fine-grained equivalent of gabbro.

True

T/F During various times in the geologic past, the polarity of Earth's magnetic field has been reversed.

True

T/F In general, rocks of the continental crust are less dense than rocks of the oceanic crust.

True

T/F In general, seafloor sediments gradually thicken away from a mid-ocean ridge.

True

T/F Olivine is an important mineral in peridotites and other ultramafic rocks.

True

T/F The Himalayan Mountains are the tectonic product of a collision between India and Eurasia that began about 40 million years ago and still continues.

True

*A ________ is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly liquid.

Vesicle

* A sandstone with the sand grains embedded in a clay-rich matrix is a ______

graywacke

*The continental drift hypothesis was rejected primarily because Alfred Wegener could not ________.

identify a mechanism capable of moving continents

*The composition of the Mantle is thought to be most similar to

peridotite

*A (an) ________ texture represents a single, long period of cooling and crystallization.

phaneritic