geology chapter 11
Place the events in order of geologic occurrence in the western United States. (Place the first/oldest event at the top.)
- 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 caused 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
During continental extension, ______.
- local mountain ranges and sedimentary basins may be formed through faulting - if nonrotating fault blocks are formed, only small amounts of extension may occur - greater amounts of extension may occur if rotating faults and blocks are formed
What features accompany the development of mountains and basins in continental collisions?
-Faulted, folded, and cleaved rocks in high mountain belts -Sedimentary basins in front of the thrust sheets -An underthrust, as one continental plate is shoved beneath another -Thrust and normal faults in the overriding plate
Rank, in order, the evolution of a continental hot spot. Put the first step on top.
-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
How may geologists determine the timing of terrane accretion?
-Studying sediment that may be derived from one terrane and deposited on another -Looking to see if the two terranes contain the same fossils -Investigating any rock units that overlie both terranes -Dating any intrusions that invade two terranes
Which of the following describe the most recent time in which all the continents were joined?
280 Ma Pangaea
The average thickness of continental crust is ______, whereas the average thickness of oceanic crust is ______.
30 to 50 km 7 km
Which areas on the map are high in elevation due to some type of tectonic collisions (continental collisions and/or subduction zones)?
A (NW US) B C E
Which locations on the image (showing a continental collision) would be more likely to support the formation of a basin?
A D E
Match the location on the image with its appropriate description
A- A large desert to the north of the Tibetan Plateau; this dessert is 3,000 m lower than the plateau and is partially filled by sediment from the adjacent highlands B- The largest, highest, and flattest plateau on Earth; average elevation is 5 km C- The world's highest mountain range, with many peaks more than 8 kn above sea level D- The world's highest mountain, rising 8,850 m above sea level
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 was 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.
Match the tectonic setting with the description of how that setting forms regional mountain belts.
A- Crust is thickened by subduction zone magma, crustal shortening, and heating and replacement of lithosphere by asthenosphere. B- Crustal thickness increases as one continent is shoved over another. C- Asthenosphere moves upward into the lithosphere and causes uplift; may occur near hot spots or plate boundaries.
Match the location on the image with the description of events for that area.
A- Extension occurs in front of the arc, causing the crust to thin by normal faulting; forms a forearc basin. B- Extension occurs behind the arc, where the crust is hot and weak; thins the crust by normal faulting. C- 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 image with the description of its place in the evolution of a continental hot spot.
A- Mantle material rises, the crust heats up, and a broad, domal uplift forms on the surface, which stretches the crust. B- Three rifts, bordered by normal faults, are well developed; the formed basins contain lakes; volcanism has begun. C- Complete rifting of the continent along two arms of the rift; new margin created and seafloor spreading started; failed rift becomes less active. D- Mid-ocean ridge moved farther out to sea; continental margin subsides and is covered by marine sediment on the new continental shelf; failed rift has rivers and a delta.
Match the letters to the correct images showing different types of continental accommodation of crustal extension.
A- Normal faults dip in opposite directions, cutting the crust into wedge-shaped blocks. B- Fault movements form basins on the dropped blocks and mountains from the upthrown blocks. C- Normal faults dip in the same direction, cutting the crust into book-shaped blocks. D- Only small amounts of extension occur with nonrotating fault blocks. E- Blocks and faults rotate, causing down-corners to become basins and up-corners to become mountains or ridges. F- Greater amounts of extension may occur with rotating faults and blocks.
Identify different geologic parts of North America (by surface rocks) by matching the areas to their descriptions.
A- The Coastal Plain made of sediment deposited in the Late Mesozoic and Cenozoic B- The Avalon Terrane from a continental collision in the Paleozoic C- The continental platform made of Paleozoic and Mesozoic rocks D- Terranes added since the Paleozoic; largest are island arcs
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 Terrances 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
Select all the possible ways in which elevation of the surface of Earth is increased.
Crustal or mantle heating beneath a region Adding magma to the crust Thrust faulting
Which of the following control the regional elevation of the land?
Density of materials in the crust Temperature of the crust and mantle Thickness of the crust
Which interpretation of the image is correct?
Different parts of the continents are of different ages.
What is true of regional elevations across North America?
Elevations tend to be higher toward the west and decrease toward the east.
Which of the following are ways in which local mountains are generally created?
Folding Volcanism Differential erosion Thrust and normal faulting
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 feature with how it may lead to the timing of terrane accretion. Intrusion that cuts across both terranes Sediment from one terrane deposited over the other Different fossils in two terranes of the same age
Intrusion that cuts across both terranes- Indicates the terranes were already together when this formed Sediment from one terrane deposited over the other- Indicates the two terranes were close enough to one another for the feature on one terrane to have been derived from the other terrane Different fossils in two terranes of the same age- Indicates terranes probably originated in different settings and locations and were not close when this feature formed
Match the geologic time to the overall geologic event that affect the western United States. Late Precambrian Paleozoic Late Mesozoic Late Mesozoic and Early Cenozoic Middle and Late Mesozoic
Late Precambrian- Rifting of Rodinia Paleozoic- Collisions Late Mesozoic- Subduction on convergent margin Late Mesozoic and Early Cenozoic- Laramide Orogeny Middle and Late Mesozoic- Extension
Match the U.S. basin with its process of formation. Michigan and Illinois Basins Gulf Coast Cascade forearc basin Paleozoic passive margin
Michigan and Illinois Basin- Probably due to Paleozoic collisional tectonics in the Appalachians Gulf Coast- Thick sequences of sedimentary rocks contained here, most likely related to Mesozoic rifting and the subsequent subsidence of the continental margin Cascade forearc basin- Sits between a volcanic arc and an offshore trench; receives abundant sediment from major rivers that drain into the sea Paleozoic passive margin- Created by rifting of the western edge of North America; locally accumulated more than 10 km of sediment
Order the positions of the continents through time, starting with 600 million years ago on the bottom of the list and the most recent event on the 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; Appalacia and Ouchita 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 situation with how it may form local mountains.
Thrust faulting- A local mountain is created if an overthrust block is uplifted faster than it is eroded or it is composed of erosion-resistant rocks. Normal faulting- One block slips down, forming a basin; the other remains high or is moved upward and can form a local mountain. 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. 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.
Choose all the possible causes of higher elevations.
Warmer rocks are in the subsurface. Region has thick crust. Less dense materials are present in the crust.
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
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.
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
Regional elevation _____________ due to normal faulting, erosion, or cooling.
changes
Crustal extension may occur due to various processes, including some of those associated with ________ and __________.
convergence subduction
A mountain or hill that remains when adjacent areas have eroded to lower elevations is a(n) _____.
erosional remnant
Isostasy ______.
explains that higher mountains have thicker crustal roots, analogous to floating icebergs was discovered by observations of surveying equipment that showed a smaller gravitational attraction by the Himalaya than expected
Tectonic terrane _____.
is bounded by faults has rocks, structures, fossils, and other geologic aspects that are unlike those in adjacent regions
The principle 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
A local mountain created by volcanism ______.
may be high in elevation but is not accompanied by a regional increase in crustal thickness
Compression rather than extension is occurring in the overlying plate because the overlying plate is ______ relative to the asthenosphere.
moving toward the subduction zone
The formation of mountains or the time period during which tectonic activity causes deformation and forms mountains is called a(n) ______.
orogeny
A continental margin that is not a plate boundary is a(n) ____ continental margin.
passive
Mountain ranges that are hundreds to thousands of kilometers long are ______, whereas other mountains that are too small to be accompanied by regional increases in crustal thickness are ______.
regional; local
These flat-lying sedimentary rocks, common in continental interiors, have ______.
remained distant from plate boundaries not been deformed
The rate of deposition of different units in a basin may be calculated by looking at their times of deposition and thicknesses; the time when sediment ______ shows when the basin began forming.
started to accumulate most rapidly
Both forearc and back-arc basins can form in areas near _________ _______.
subduction zones.
A fault-bounded body of rock that has a different geologic history than adjacent regions is called a ______.
tectonic terrane
Two well-known regions of currently active continental hot spots are ______.
the Afar region in East Africa, and Yellowstone National Park in North America
The Himalaya is
the highest mountains in the world and contains Earth's highest peak
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 subducted slab relative to the asthenosphere or it is moving away
Flat-lying sedimentary rocks are common in continental interiors because ______.
they were deposited and have remained away from plate boundaries
Crust that is compressed and shortened by thrust faults is also ______.
thickened, causing uplift and an increase in elevation
Folding can make a local mountain by ______.
warping and uplifting Earth's surface and underlying rock layers
