Earth Science Ch. 7

Concepts of "stress" and "strain" are related because _______.

"Stress" causes "strain"

The Peninsular terrane is now part of the crust of North America in Southern Alaska. The dominant rock type in this terrane is intrusive igneous rock that ranges in composition from gabbro to granite and volcanic rock with a similar compositional range. Geologic evidence indicated the Peninsular terrane collided with North America during late Mesozoic time. Which of the following would be the most reasonable tnterpretation for the origins of the Peninsular terrane?

A Mesozoic island arc

What type of basin would be most likely to contain large amounts of sediments derived from a volcanic source?

A forearc basin.

What is the difference between a hanging wall and a footwall?

A hanging wall is the overhanging rock unit of the slant that separates the two slabs, while the footwall is below the slant.

What is the major difference between a subduction zone and a collisional mountain chain?

A subduction zone has active volcanism.

An ______ is thick accumulation of sediments and small tectonic blocks formed of material scraped off subducting oceanic lithosphere at a convergent margin.

Accredtionary-wedge complex.

In what part of a subduction margin might you find rocks deposited on the abyssal plain, far from land?

Accretionary Wedge

You are walking on the beach along the south-coast of Alaska. You see rocks cut by numerous faults that consist of basalt with evidence of eruption in the ocean, deep-water chert, mudstone, and sandstones with abundant volcanic material. What tectonc setting would you assign to these rocks?

Accretionary wedge

Mountain building in the western margin of North America records a history of both ______.

Adean type subduction and terrane accretion

The west coast of California is underlain by rocks that represent ______.

An ancient Forarch and accretionary wedge.

Granitic batholiths typically form over time intervals of ______. These are normally formed below the surface of the earth.

Billions of years

The Himalayas and Tibet are the archetypical example of a ______ mountain belt?

Collisional

In the figure, the stress of block 'X' is ______.

Compressional

The Tibetan plateau is high above sea level because ______.

Crustal thickening over millions of years has produced a thick crust that stands high due to Isostasy

When subjected to a differential stress, a very "brittle" material, like glass, will ______.

Deform by breaking or elastic bending

This area represents what type of mountain system?

Fault block mountains

Burial of rocks increases the confining pressure so that deeply buried rocks are more likely to ______ than shallow rocks.

Fold

he Sierra Nevada Mountains of California, and the Teton Mountains of Wyoming, ranges are examples of ______.

Foult blocks uplifted by late Teriary to Quaternary normal faulting.

Which of the following statements is most likely to be true based on the diagram?

If is the product of extensional forces.

A widely cited theory associates active faults with earthquakes in China and Southeast Asia. This theory suggests ______.

India is plowing into the "soft underbelly" of Asia, pushing East Asia eatward

The diagram below is an example of what plate tectonic setting?

Island Arc

The Rocky Mountains of western North America were produced in an orogeny called the ______.

Laramide orogeny

Folded limestones that are exposed high elevations in the Himalayas were originally deposited as sediments in a ______.

Marine basin between India and Eurasia.

Orogenesis refers to the formation of ______.

Mountains

Subduction occurs when ______ rocks are forced beneath ______ rocks.

Oceanic; continental or oceanic

What is the modern theory for orogenesis (mountain building)?

Plate tectonics theory

Southwestern North America contains a large area called the Basin and Range province. What is the origin of this name?

Ranges are uplifted horst blocks while basins formed as grabens.

In a ______ fault, the hanging wall block moves up with respect to the footwall block.

Reverse

A thrust fault increases the thickness of the crust as it move toward a continental interior in a mountain belt; yet the crust beyond the mountain front stays the same thickness. Isostasy would suggest that the area at the mountain front, where the thrust emerges, should ______ over time.

Subside

In the interior of continents the earth's crust is typically about 40km thick and the elevation is near sea level. Most earth materials expand when heated, lowering their density. During rifting continental margins are heated but cool as sea floor spreading moves offshore from the continent. Thus, basic isostasy suggests that after rifting, a continental margin will ______.

Subside

The type of fold that has the two limbs at the same angle is called a ______.

Symmetrial fold

In the figure, the stress on block 'Y' is ______.

Tensional

Most granitic batholiths represent ______.

The exhumed roots of a subduction related magmatic arc

Ocean spreading centers are highlands on the ocean floor, sometimes referred to as submarine mountains. Oceanic crust worldwide is about the same thickness so isostasy would suggest the ocean floor should be as flat as Kansas. Which of the following statements best describes the origin of these submarine mountains?

The mantle beneath the ridges remains hot for millions of years producing an elevated region along the ridge axis because hot rocks are lower density than cold rocks.

The Appalachian Mountains may have once been as lofty as the Himalayan-Tibetan Mountain belt is today. Why are they not this high now?

They formed long ago, and erosion has beveled them to their present low elevation.

Based on you knowledge on isostasy, would you expect thicker or thinner crust beneath the Caribbean Islands than the continental region of Venezuela to the south?

Thinner - because the area is mostly above sea level.

Mountain building uplifts rocks against the force of gravity raising their potential energy, which requires work by the earth system. Based on the relative motion of fault blocks, what type of fault would you expect to require more energy than the others?

Thrust

Which way does syncline go?

U shape

The ______ is characterized by terrane accretion that have been active throughout most of Mesozoic and Cenozoic time.

Western margin of north America

In the figure, which of the deformations appears most similar to what might be expected along a divergent plate boundary?

Y

In the figure, which of the deformations appears most similar to what might be expected along a transform plate boundary?

Z

A transform fault is ______.

a strike-slip fault that forms the boundary between tectonic plates

In a monocline, the upper and lower limbs of the fold ______.

are horizontal

Large circular downwarped structures are called ______.

basins

The Appalachians were formed by three phases or ______ orogeny.

collisional

Terrane accretion generally occurs along a ______ boundary between a continental plate and a ______ plate.

convergent; continental

Changes in the shape of a rock body in response to a differential stress is called ______.

deformation

The higher the temperature, the more likely it is that a rock will deform in a ______ manner.

ductile

The material in the figure exhibited ______ behavior when the folding occurred.

ductile

Folds are an example of ______.

ductile deformation

Most active faults pose a risk to society because they can potentially produce ______.

earthquakes

A good example of a present-day, passive continental margin is the ______.

east coast of North America

The area labeled C shows an active fault bounding the range. Which best describes the motion on the fault?

east side up

When the differential stress exceeds the strength of the material, the material will begin to undergo ______.

elastic strain

Monoclines, anticlines, synclines, and domes are all examples of ______.

foliation

Fractures in rock with no offset (where there has been not motion) are called ______.

joints

Studies of the chemistry of rocks from arc volcanoes indicate the main source of the magma is ______.

melting of the asthenosphere above the subducting oceanic plate by fluids acting as a flux to enhance melting.

In the interior of continents the earth's crust is typically about 40km thick and the elevation is near sea level. In an area where the crust in 20km thick, isostasy would suggest the elevation in the area would be ______ unless the density changes from one area to the other.

near sea level

A ______ fault forms when the hanging wall moves down relative to the footwall.

normal

Grabens are formed by what type of faulting?

normal

When the hinge line of a fold is not horizontal the fold is said to ______.

plunge

In the figure, the stress of block 'Z' is ______.

shear

The term "cordillera" comes from a word meaning ______.

spine

A ______ fault has little or no vertical movements of the two blocks.

strike-slip

The San Andreas Fault in California and the Alpine Fault in New Zealand are examples of ______.

strike-slip faults

Island arcs and Andean type mountains are both examples of mountains formed by ______.

subduction

The boundary between two terranes or two continents that have collided is called a ______.

suture

Any accreted crustal fragment that has a geologic history distinct from that of the adjoining fragments is termed a ______.

terrane

Island arc systems now on the Tibet plateau record subduction prior to the collision of India with Eurasia. Geologists would map these pre-collisional arc rocks as ______.

terranes

In thrust faulting, ______.

the crust is shortened and thickened

Most geologists think that the elevation of mountains above sea level is limited by earth's gravity because ______.

thickening of the crust in mountain belts produces a weak deep crust that spreads by gravity collapse, limiting the elevation.

Exhumed basins contain ______ rocks in the center of the structure and domes contain ______ rocks in the center.

younger; older