Chapter 11: Mountains, Basins, and Continents

Regional elevation _________ due to normal faulting, erosion, or cooling.

decreases

The formation of mountains or the time period during which tectonic activity causes deformation and forms mountains is called an __________.

orogeny

A continental margin that is not a plate boundary is a _______ continental margin.

passive

Basins formed by strike-slip faults are called ________ pull-apart basins.

pull-apart

Hot spots have helped define the outlines of the continents by:

shaping the boundaries along which continents separate, due to location of the rift arms

A fault-bounded body of rock that has a different geologic history than adjacent regions is called a _______.

tectonic terrane

What types of terranes have been added to or displaced in California

+Accretionary prism of oceanic material +Mesozoic island arcs +Slices of Paleozoic and Mesozoic oceanic crust and sediment +Displaced granitic rocks

Select all the possible ways in which the elevation of the surface of the Earth is increased.

+Thrust faulting +Adding magma to the crust +Crustal or mantle heating beneath a region

The thickness of the lithosphere is, on average, about _____, and ranges form near _____ at the mid-ocean ridges to more than _____ beneath some ancient continental interiors.

100 km; 0 km; 150 km

The average thickness of continental crust is _______, whereas the average thickness of oceanic crust is _______.

30 to 50 km 7 km

A prism- or wedge-shaped, structurally complex zone of faults, folds, and mostly metamorphosed rocks that forms along the upper parts of a subduction zone where sedimentary material and oceanic crust are scraped off the downgoing slab is called a(n) ______.

Accretionary Prism

Which represent some original tectonic settings of terranes?

Deep-ocean crust. Pieces rifted off another continent. Island arcs. Oceanic islands or plateaus.

Which interpretation of the image (Rainbow'd world map) is correct?

Different parts of the continents are of different ages.

Match the situation with how it may form local mountains. Folding

It warps and uplifts earth's surface as well as the underlying rock layers; uplift of a hard layer can create a local mountain.

Match the feature with the description of how it relates to continental interiors. Crystalline basement

Metamorphic and igneous rocks underlie much of the continent.

Changes in global climate

Sea-level rise can cause significant flooding well into the interior of a continent.

Match the location on the image of ocean-continent convergence with the process for its formation. A - subduction zone

Subduction creates deep oceanic trench, which acts as a deep oceanic basin.

Match the location on the image of ocean-continent convergence with the process for its formation. B - hotspot

Subduction-related mountain belt thickens by the addition of volcanic rock at and below the surface.

Match the location on the image with its appropriate description. B - Tibetan Plateau

The largest, highest, and flattest plateau on Earth; average elevation is 5 km.

For a terrane to become attached to a continent, it typically:

enters a subduction zone, where it is scraped off the subducting plate and added to the continent

A tectonic terrane can be defined as

having rocks, structures, fossils, and other geologic aspects that are unlike those in adjacent regions being bounded by faults

The principal that regional elevations adjust to the types and thicknesses of rocks at depth is known as __________.

isostasy

Uplift caused by the removal of weight on top of the crust, as when an ice sheet melts away or when erosion strips material off the top of a thick crustal root of a mountain, is called ______

isostatic rebound

Basins formed by normal faulting are called ________ basins.

normal-fault

Isostatic rebound is _______________.

the uplift of crust that occurs after an overlying mass has been removed, such as when an ice sheet melts away or when erosion strips material off the top of a thick crustal root of a mountain

Crust that is compressed and shortened by thrust faults is also __________.

thickened, causing uplift and an increase in elevation

Which of the following would explain thick crust?

Crust has been compressed from the sides; may create faults and/or folds. Crust is continental. Crust undergoes deposition of sediment or addition of volcanic rocks.

Match the feature with how it may lead to the timing of terrane accretion. Indicates the terranes were already together when this formed.

Intrusion that cuts across both terranes. Single rock unit overlying the two terranes.

An accretionary prism is ____________.

a wedge-shaped zone of faults, folds, and metamorphosed rocks formed along the upper parts of a subduction zone as material is scraped off.

Match the supercontinent with its description. Rodinia

all the continents were joined; existed from about 1.1 Ga to about 600 Ma.

Match the supercontinent with its description. Pangaea

all the continents were joined; existed from about 250 Ma to about 200 Ma.

Match the orogeny with its cause.

Taconic About 450 Ma, an island arc collided with the North American continental margin. Acadian About 400 Ma, Avalonia collided with and was thrust over eastern North America. Alleghian About 300 Ma, Gondwana overrode the eastern edge of North America.

Match the location on the image with a description of how that area may help determine the age of the basin.

A A unit younger than a basin may overlap the edge of the basin and its faults, showing that the basin had stopped forming by the time the unit with developed. B Units deposited during formation of a basin may be very thick and may contain coarse sediments that record steep slopes along the flanks of the basin. C Units older than a basin typically have the same thickness across the area and were then tilted and faulted when the basin formed. D Rate of deposition of different units may be calculated by looking at their times of deposition and thicknesses; the time when sediment started to accumulate most rapidly shows when the basic began forming.

Match the different parts of North America with the appropriate description.

A The region contains the oldest dated rocks (4.0 billion years old) in North America. B The area contains many terranes accreted during the Paleozoic, Mesozoic, and Cenozoic. C Late Precambrian and Paleozoic terranes accreted during the formation of the Appalachian Mountains. D The Grenville Province terrane was accreted 1.1 billion years ago. E Rocks on the Canadian Shield are 3.0 to 1.7 billion years old.

Match the location of the image with the best approximation of lithospheric thickness at that location.

A nearly 0 km B 70 km C 100 km D 140 km

Match the tectonic setting with the description of how that setting forms regional mountain belts.

A (subduction zone) Crust is thickened by subduction zone magma, crustal shortening, and heating and replacement of lithosphere by athenosphere. B (other one) Crustal thickness increases as one continent is shoved over another. C (arrows pushing up a mountain) Asthenosphere moves upward into the lithosphere and causes uplift; may occur near hot spots or plate boundaries.

Match the region on the image with the description of events for that area.

A (subduction zone) Extension occurs in front of the arc, causing the crust to thin by normal faulting; forms a forearc basin. B (on island) Extension occurs behind the arc, where the crust is hot and weak; thins the crust by normal faulting. C (in water behind island) Extension behind the arc may be great enough to form a back-arc basin with a small-scale version of a mid-ocean ridge.

Match the location on the image with its appropriate description. A - Tarim Basin

A large desert to the north of the Tibetan Plateau; this desert is 3,000m lower than the plateau and is partially filled by sediment from the adjacent highlands.

Match the situation with how it may form local mountains. Thrust faulting

A local mountain is created if overthrust block is uplifted faster than it is eroded or it is composed of erosion-resistant rocks.

Which locations on the image (showing a continental collision) would be more likely to support the formatino of a basin? (Choose all that apply)

A: A foreland basin can form in front of the collision zone as one plate is forced under the other. D: Crust that gets too thick or hot may begin to spread under its own weight, forming normal faults and the development of associated basins. E: Behind a collision zone, a basin can be formed as weight of the thrust sheets in adjacent crust pushes the region down.

Match the image with the description of events depicted, leading to the formation of the Appalachian and Ouachita Mountains in North America (N.A.).

A: Initial Rifting occurs along eastern N.A.: starts within Rodinia. B: Seafloor spreading creates new ocean basain; eastern coast of N.A. becomes passive margin. C: Convergent margin forms; creates an island arc that later collides with N.A. D: Avalonia collides with N.A. during the Acadian orogeny; foreland basin created for the Catskill Delta E: Alleghenian orogeny: Gondwana collides with N.A.: Appalacians form along eastern N.A., while Ouachitas form along sourthern N.A.

What types of terranes that have been added to or displaced in California?

Accretionary prism of oceanic material. Displaced granitic rocks. Slices of Paleozoic and Mesozoic oceanic crust and sediment. Mesozoic island arcs.

Match the approach to timing the uplift of a region with its description and how it relates to the investigation of the Himalaya. Clasts in adjacent sedimentary basins

Age of uplift may be determined when pieces of rock from a mountain were added to the sedimentary sequence; sediment from the Himalaya first appeared around 45 million years ago.

Which features accompany the development of mountains and basins in continental collisions?

An underthrust, as one continental plate is shoved beneath another. Faulted, folded, and cleaved rocks in high mountain belts. Sedimentary basins in front of the thrust sheets. Thrust and normal faults in the overriding plate.

Match the supercontinent with its description. Gondwana

Antarctica, Australia, South America, and Africa were joined together in the southern hemisphere; existed from nearly 600 Ma to about 150 Ma.

Basins may form _______.

As a result of normal faulting. Along plate margins. On both oceanic and continental plates.

Match the approach to timing the uplift of a region with its description and how it relates to the investigation of the Himalaya. Isotopic dating methods

As deep rocks are uplifted, they cool and lock in daughter products from radioactive decay; in the Himalaya, some of the show ages as young as several million years.

Show how deeply formed rocks are exposed in eroded mountain belts, starting with early mountain building on top.

As the mountain belt forms, uplift is faster than erosion and the mountain grows. Weathering and erosion begin to wear down the mountain as uplift slows. As erosion continues, less weight holds down the crustal root, and isostatic rebound causes uplift. Continuing erosion and isostasy cause rocks deep in the crust to be uplifted and exposed at the surface.

Match the tectonic setting with its connection to the formation of basins. Strike-slip faults

Basins may develop if one block drops down relative to another in this mostly horizontal movement fault, or pull-apart basins may develop where motion along nearby faults causes the crust to pull apart.

Match the feature with the description of how it relates to continental interiors. Continental platform

Broad region surrounding the central area is characterized by nearly horizontal sedimentary rocks that were deposited on top of the basement.

The image shows what portions of Africa and South America may have looked like 110 million years ago, after the continents started to rift apart. Based on the developing continental outlines and the failed rift, identify the most likely location of the continental hot spot responsible for the rifting.

C

Tectonic activity along continental margins

Causes broad uplifts and basins within the continent in response to loading of sediments along the margin and the emplacement of thrust sheets.

Match the feature with the description of how it relates to continental interiors. Continental shield

Central region consists primarily of Precambrian metamorphic and igneous rocks.

The geologic history of a continental interior can be affected by:

Changes in global climate and the rise and fall of sea level Movement of the plate upon which it rides (change in latitude) tectonic activity along the edges of a continent

Which are true regarding the thickness of continental versus oceanic crust?

Continental crust is thicker than oceanic crust. Oceanic crust averages 7km in thickness. Continental crust averages 30 to 50 km in thickness.

True/False: Crustal extension cannot occur near subduction zones

False

Which are ways in which local mountains are generally created?

Folding Volcanism Differential erosion Thrust and normal faulting

Match the basin type with its description

Forearc basin: A sedimentary basin that lies between the volcanic arc and the trench in a convergent plate boundary Foreland basin: A basin that forms when crust is warped by the weight of thrust sheets, especially when formed between a mountain belt and continental interior Pull-apart basin: A basin that forms as the result of movement within a zone of strike-slip faulting Normal-fault basin: A low area that has been downdropped b one or more normal faults

Match the tectonic setting with its connection to the formation of basins. Regional subsidence

Huge basins form where a broad region drops in elevation; may be due to regional cooling or density changes.

Match the US basin with its process of formation. Cascade forearc basin

Sits between a volcanic arc and an offshore trench; receives abundant sediment from major rivers that drain into the sea.

Using the rule of thumb for elevations and the information provided by the image, what may be said of the actual differences in elevation and crust thickness between Phoenix and Flagstaff (elevation Phoenix: 300m, Flagstaff: 2,100m)?

The differences are what we would predict. Rule of thumb: increase of 6km crust thickness = increase in 1km elevation

Numerous terranes exists in Alaska. One of these is the Wrangellia terrane. Why is the Wrangellia terrane considered to be part of the same terrane as that scattered in pieces from western Idaho northward to Alaska?

The terranes have similar ages and sequences of rocks.

Match the location on the image with its appropriate description. C - Himalaya

The world's highest mountain range, with many peaks more than 8 km above sea level.

Match the location on the image with its appropriate description. D - Mt. Everest

The world's highest mountain, rising 8,850 m above sea level.

The process of adding a terrane to another landmass is called __________.

accretion

Two well-known regions of currently active continental hot spots are ____________.

the Afar region in East Africa, and Yellowstone National Park in North America.

Subduction is not always accompanied by compression and thrust faulting in the overriding plate. this is especially true when ________.

the overriding plate is either not moving toward the subjected slab relative to the asthenosphere or it is moving away

Folding can make a local mountain by _______.

warping and uplifting Earth's surface and underlying rock layers

Match the situation with how it may form local mountains. Differential erosion

A rock not easily weathered resists erosion and also may protect softer rocks beneath it from erosion; the area is left higher than the surroundings and may form an erosional remnant, ridge, or a mesa.

Match the feature with the description of how it relates to continental interiors. Unconformity

Boundary between flat-lying platform sedimentary rocks and underlying crystalline rocks separates rocks with very different ages and geologic histories.

During the Paleozoic, the Catskill Delta existed in what is now the eastern United States.

Composed of sediment eroded from the Appalachian Mountains. Contained within an ancient foreland basin. Sediment coarser and thicker to the east.

Which situations would result in a relatively higher regional elevation?

Dense lithosphere replaced by less dense asthenosphere. A region with thin lithosphere (such as the mid-ocean ridge)

Which control the regional elevation of the land?

Density of materials in the crust. Temperature of the crust and mantle. Thickness of the crust.

Match the approach to timing the uplift of a region with its description and how it relates to the investigation of the Himalaya. Finding rocks at higher elevations that were deposited at low elevation

Determine general amount of uplift; the top of Mount Everest contain limestone that was deposited below sea level and later uplifted to over 8,800 m.

Match the feature with how it may lead to the timing of terrane accretion. Indicates terranes probably originated in different settings and locations and were not close when this feature formed.

Different fossils in two terranes of the same age.

Which may affect crustal thickness?

Erosion. Deposition or burial by volcanic rocks. Type of crust (continental or oceanic). Deformation (such as compression or stretching).

The Ural Mountains in Russia are a mountain range in the middle of a continent because

Europe collided with Siberia 200-300 mya, forming a range in the center of the new continent as the landmasses joined.

How can folding form a topographic high?

Folding can cause warping and uplift. A folded, hard layer can be uplifted and more resistant to erosion than surrounding rocks.

Match the tectonic setting with its connection to the formation of basins. Continental rift

Normal faults create downdropped blocks that accumulate sediment; may evolve into a passive margin.

Match the image showing different types of continental accommodation of crustal extension with the best descriptions of events. A - wedge-shaped non-rotated blocks.

Normal faults dip in opposite directions, cutting the crust into wedge-shaped blocks. Fault movement form basins on the dropped blocks and mountains from the upthrown blocks. Only small amounts of extension occur with nonrotating fault blocks.

Match the supercontinent with its description. Laurasia

North America, Europe, and Asia were joined in the Northern Hemisphere; existed from 250 Ma to about 150 Ma.

Order the positions of the continents through time, starting with 600 million years ago on bottom to the most recent event on top.

Present-day configuration of the continents and oceans found. North America separated from Africa and South America; Atlantic Ocean forms; Laurasia and Gondwana are the supercontinents. Pangaea formed; Appalachian and Ouachita Mountains created. Europe and North America joined; Avalonia collided with North America. Continents dispersed; Gondwana was formed in the Southern hemisphere. All major continents were joined as Rodinia.

Match the US basin with its process of formation. Michigan and Illinois Basins

Probably due to Paleozoic collisional tectonics in the Appalachians.

Rank, in order, the evolution of a continental hot spot.

Rising mantle material first encounters the base of the lithosphere. Domal uplift forms at the surface, stretching the crust. Rift arms are formed by faulting, and eruptions of lava begin. Complete rifting of the continent occurs along two arms of the rift, while the third arm becomes inactive. Seafloor spreading continues and a passive continental margin is created as the mid-ocean ridge moves farther out to sea.

Match the feature with how it may lead to the timing of terrane accretion. Indicates the two terranes were close enough to one another for the feature on one terrane to have been derived from the other terrane.

Sediment from one terrane deposited over the other.

Which are tectonic settings in which regional mountain belts form?

Subduction zones Continental collisions Mantle upwellings

Match the regional/global with its influence on the geologic history of a continental interior.

Tetonic activity along continental margins: It causes broad uplifts and basins within the continent in reponse to loading of sediments along the margin and the emplacement of thrust sheets. Changes in global climate: Sea-level rise can cause significant flooding well into the Interior of a continent. Rise of mountains along a coast: Weather patterns can change, causing a change in climate; as an example, rain-shadow deserts may form. (Consider US west coast mountain ranges) Movement of the tectonic plate on which the continent rides: Latitude can be changed over time, causing drastic changes in climate of the area.

Match the US basin with its process of formation. Gulf Coast

Thick sequences of sedimentary rocks contained here, most likely related to Mesozoic rifting and the subsequent subsidence of the continental margin.

Below are listed reasons why regions have either higher or lower elevations. Choose the causes of higher elevation.

Warmer rocks are in the subsurface. Region has thick crust. Less dense materials are present in the crust.

Rise of mountains along a coast

Weather patterns can change, causing a change in climate; as an example, rain-shadow deserts may form.

Match the location on the image of ocean-continent convergence with the process for its formation. D - past mountains

Weight of the thrust sheets causes the continent to flex downward and forms a foreland basin.

A mountain or hill that remains when adjacent areas have eroded due to lower elevations is an ____________.

erosional remnant

Low areas that lie between a trench and the volcanic arc are ________ basins.

forearc

Low areas that form between a mountain belt and the continental interior are ________ basins.

foreland

Match the location on the image of ocean-continent convergence with the process for its formation. C - interior mountains

Convergence causes horizontal compression and creates a fold and thrust belt behind the main mountain belt.

Match the US basin with its process of formation. Paleozoic passive margin

Created by rifting of the western edge of North America; locally accumulated more than 10km of sediment.

Match the tectonic setting with its connection to the formation of basins. Reverse and thrust faults

Foreland basin occurs when crust is depressed by the weight of thrust sheets; forearc basins may arise form in accretionary prisms.

Volcanism creates mountains that are _______.

Formed of piled volcanic material, such as scoria, ash, lava, flows, debris flows, and mudslides. Sometimes local and not accompanied by regional increases in crustal thickness. Varied in size from small cinder cones to large shield and composite volcanoes.

Match the approach to timing the uplift of a region with its description and how it relates to the investigation of the Himalaya. GPS observations

Give direct measurements of uplift; parts of the Himalaya are rising a few centimeters per year.

Continental interiors tend to ____________.

Have a central region called a continental shield and a surrounding region called a continental platform. Be tectonically stable and far from plate boundaries. Contain sedimentary rocks that have important records of past environments and events.

Match the tectonic setting with its connection to the formation of basins. Passive margin

Largest type of basin; underlain by thin, previously rifted crust; receives sediment from the continent.

Movement of the tectonic plate on which the continent rides.

Latitude can be changed over time, causing drastic changes in climate of the area.

The Michigan Basin is pictured in the images. What may be said of this basin?

Layers are thicker in the center of the basin, indicating the basin was subsiding during deposition. Rock layers form a bull's-eye pattern with the youngest rocks in the center, indicating the presence of the basin. It may have formed during an episode of continental rifting.

What is true of the difference between regional mountain ranges and local mountains?

Local mountains are small features and do not involve regionally thickened crust. Regional mountain ranges are typically very long and involve regionally thickened crust.

Match the image showing different types of continental accommodation of crustal extension with the best descriptions of events. A - rectangular rotated blocks.

Normal faults dip in the same direction, cutting the crust into book-shaped blocks. Blocks and faults rotate, causing down-corners to become basins and up-corners to become mountains or ridges. Greater amounts of extension may occur with rotating faults and blocks.

Match the possible tectonic origin with the terrane description.

Oceanic crust Pillow basalt, deep-sea sediment. Island arcs Andesitic volcanic rocks and volcanic derived sedimentary rocks. Piece rifted off another continent Thick granitic crust and continental sediment and rocks.

Match the situation with how it may form local mountains. Normal faulting

One block slips down, forming a basin; the other remains high or is moved upward and can form a local mountain.

Which may be said about the geologic history of east and southeast North America?

Rifting once again occurred around 200 Ma and created the Atlantic Ocean; North America underwent a cycle of rifting, collisions, and rifting. Convergence and collisions occurred between about 500 Ma to 220 Ma, causing the Taconic, Acadian, and Allgehnian orogenies. Rifting occurred to separate North America from Rodinia around 600 Ma.

Place the events in order of geologic occurrence in the western US.

Rifting thinned the crust along the western edge of North America; west became a passive margin with a broad shelf. Island arcs formed offshore and began to collide with the edge of the continent; Ancestral Rockies formed due to collisions in the east. Subduction along the western edge cause volcanism; inland, the continent flexed down, causing widespread flooding. Subduction began to occur at a lower angle and caused the Laramide Orogeny. Part of the convergent margin became transform (the San Andreas fault); Basin and Range Province and Rio Grande Rift formed.

Rank the following features in order of encounter, from the West Coast on top to the East Coast of North America.

Sierra Nevada Moderately high elevation. Basin and Range Largely due to very thin lithosphere. Colorado Rockies compression and shortening of the North American Plate. Great Plains Elevation decreases toward the east, as lithosphere gets cooler and thicker. Appalachian Mountains Ancient collision of North America and Africa; elevation lessened by erosion.

Match the mountain or plateau location with its tectonic setting.

Western Canada Convergent margin collisions; thickened crust. Andes Above a subduction zone; magmatic additions and crustal thickening. Alps Collisions between Europe and smaller continental blocks from the south. East African Rift Magmatic heating of the crust, thinning of the lithosphere, mantle upwelling. Tibetan Plateau and Himalaya Continental collision of India and Asia. Great Divide Range in eastern Australia No plate boundary currently there; geologists investigating the cause of the uplift.

Isostasy ______ (check all that apply)

was discovered by observations of surveying equipment that showed a smaller gravitational attraction by the the Himalaya than expected explains that higher mountains have thicker crustal roots, analogous to floating icebergs