GEL-101 Ch. 8, 11, & 18
A. Which of the following factors describes the conditions at a zone where contact metamorphism is occurring? B. What is a metamorphic aureole? C. How is quartz sandstone metamorphosed into quartzite during contact metamorphism? D. Which of the following best describes confining pressure and the location in which it occurs?
A. -high temperature -low pressure B. a ring of metamorphic rocks adjacent to an igneous intrusion C. Sand grains are fused together because of high temperatures. D. moderate pressures at shallow depths
Which metamorphic feature is associated with contact metamorphism?
metamorphic aureole
By applying the law of superposition ________ dates can be determined.
relative
The time period of "ancient life" is the ________ era.
Paleozoic
Part A A graben is characterized by ________.
a hanging wall block that has moved down between two normal faults
Which of the following forces applies stress or pressure that is equal in all directions?
confining pressure
Which of the following is the result of brittle deformation?
a reverse fault
Calcite is the main mineral constituent of the sedimentary rock limestone and of the metamorphic rock marble.
True
A horst is ________.
an uplifted block bounded by two normal faults
What term describes the zone of contact metamorphism surrounding an intrusive magma body?
aureole
Which of the following lists the rocks in the order of increasing grain size and increasing grade of metamorphism?
slate, phyllite, schist
ITEM 1-18-B Part B In the images below, which contains a disconformity?
B. SEE IMAGE A, C, D, & E ON CARDS #87-91
Word Analysis. Examine the words and/or phrases for each question below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.
melting
Which rock has the finest grain size?
slate
Which era of geologic history do geologists know the most about?
Cenozoic
*Not a question on the lab* The Types of Folds Compressional stresses will create folds under high temperatures and there are two main types of folds: 1. Anticlines: where the rocks create an upward arch, and 2. Synclines: where the rocks are curved downward into a trough.
*Not a question on the lab*
Which of the following is an example of ductile deformation? Choose all that apply.
-an anticline -a dome -a syncline
________ is an erosional contact between tilted, older strata below and horizontal, younger strata above.
An angular unconformity
Which nonfoliated metamorphic rock is easy to shape into decorative stones?
Marble
________ forms from the metamorphism of limestone or dolostone.
Marble
Faults are fractures in the brittle upper crust where significant displacement has taken place due to rock movement. Dip-slip faults are faults in which the movement is parallel to the dip (or slope) of the fault. When discussing movement along nonvertical faults, the hanging wall occurs above the fault and the footwall occurs below the fault. There are three main types of dip-slip faults: Normal faults are dip-slip faults where the hanging wall block moves down relative to the footwall block, and they occur when the crust is extended, or lengthened. Reverse faults are dip-slip faults where the hanging wall block moves up relative to the footwall block, and they occur during compressive shortening of the crust. Thrust faults are dip-slip faults where the dip of the fault is less than 45∘∘, causing the movement of the hanging wall to be nearly horizontal to the fault surface. Thrust faults are most common in convergent plate margins due to compressive forces and the abundance of folded layers.
NOT A QUESTION
The ordering of events in geological history has long been a difficult task but once simple principles were determined, observation and logic could be used to determine the order of events. With these principles, one cannot calculate the exact number of years ago an event occurred, but instead the sequence of events can be determined. This is referred to as relative dating. The principles are as follows: The principle of superposition: In sedimentary rocks, the rock bed on the bottom must be older than the rock bed on the top. The principle of original horizontality: Sedimentary rocks were originally deposited as flat-lying, horizontal layers. The principle of cross-cutting relationships: Any rock or feature cutting through another rock or feature must be younger than the material through which it cuts. (For example, with faults, the first rock must be there for these secondary features, such as igneous intrustions like dikes or fractures, to cut through.) Inclusions: Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.)
NOT A QUESTION
A good example of a present-day, passive continental margin is the ________.
east coast of North America
A(n) ________ fault has little or no vertical movements of the two blocks.
strike slip
Which natural processes act as metamorphic agents? Choose all that apply.
-differential stress from mountain building -differential stress at a convergent plate boundary -heat from magma intrusion
What kinds of rocks can become metamorphic rocks? Choose all that apply
-metamorphic rocks -igneous rocks -sedimentary rocks
Part A What is the best way to date a sedimentary rock? Choose all that apply.
-relate the sedimentary rocks to datable igneous intrusions -use index fossils
ITEM 1-3-Part B B - A Change in Shape caused by Stress: Terminologies Part complete Complete the following sentences regarding deformations resulting from stress. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. You do not need to use all terms.
1. Large rifts or valleys, which can often have very large normal faults, are created by tensional forces. 2. If a rock undergoes folding and is compressed to form an upward arch, this is a(n) anticline type fold. 3. A trough, or downward fold, called a(n) syncline is formed when a rock is deformed through folding. 4. When a rock is under undue stress and fractures but there is no movement to either side of the fracture, the feature is a called a joint. If, however, there is movement, it is called a fault.
ITEM 1-6-B Part B - The Geologic Time Scale and Unconformities Gaps in the rock record are called unconformities. Unconformities are caused by periods of erosion that have occurred between periods of deposition, which have erased a portion of the rock record. There are three types of unconformities: (1) angular unconformities occur when tilted strata are overlain by horizontal strata—Click here to see an angular unconformity; (2) disconformities occur when strata are separated by an erosional surface—Click here to see a disconformity); (3) nonconformities occur when strata overlay igneous or metamorphic rocks that are resistant to erosion—Click here to see a nonconformity. Study the geologic time scale below which subdivides the 4.6-billion-year history of Earth into several units, outlining the time frames of several events of the geologic past. Pay particular attention to the Triassic to Quaternary periods. -Now use the figure below, which has labeled each of the rock strata/layers with their respective geologic time periods, to fill in the gaps in the following sentences. -Match the words in the left column to the appropriate blanks in the sentences on the right.
1. The Triassic and Cretaceous rocks are separated by this type of unconformity: an angular unconformity. 2. The Quaternary and Tertiary rocks are separated by this type of unconformity: a disconformity. 3. The dike dates to the Tertiary period. 4. The tilted rocks must have been most likely tilted during or after the Triassic period. 5. Due to an unconformity, the Jurassic period is missing from the rock layer record. SEE 2ND IMAGE ON CARD 70
A. Which of the following factors describe the metamorphic conditions at a mid-ocean ridge? Choose all that apply. B. Which of the following factors describe the metamorphic conditions in a subduction zone? C. Which of the following is a metamorphic rock? D. Which of the following is a temperature associated with metamorphism?
A. -hot, watery fluids -low temperature -low pressure B. -low temperature -high pressure C. gneiss D. 400 degrees Celsius
A. Which of the following scenarios best describes the deformation that will occur in different parts of the crust? B. Which of the following is an example of how rocks will respond to compressional stress? (Note: there may be more than one correct answer.) Check all that apply. C. Which tectonic stress will result in a lengthening of the crust? D. Which of the following images best describes how a rock in the deep crust would be deformed as a result of shear stress?
A. Brittle deformation is dominant in the shallow crust; ductile deformation is dominant in the deep crust. *Correct Temperatures are lower near to the surface, making the rock "cold" and more likely to shatter. B. -folding -reverse faulting *Correct -Reverse faults occur when the landscape is shortened. -Folding occurs when the landscape is shortened. C. tension *Correct Tensional stress pulls things apart. D. SEE IMAGE *Correct Because the rocks are at depth, the rocks will distort, but not fracture.
Part A Which mountain range marks the boundary between the Indian and Eurasian Plates? Part B What kind of tectonic boundary is currently responsible for creating the Himalayas? Part C What geologic features were created in the Eurasian Plate when India underthrust beneath it? Choose all that apply. Part D As India moves northward, China and Southeast Asia are being relocated to the east and southeast because of "escape tectonics." What feature is allowing them to "escape"? Part E When the Indian Plate collided with Eurasian Plate, why didn't it subduct?
A. Himalayas Correct Because of the interaction between these two plates, the Himalayas are still growing. B. Continent-Continent Convergent Boundary Correct The Indian Plate, which is continental, is currently sliding into the Eurasian Plate, also continental. C.-thrust faults -thicker continental crust Correct Thrust faults result from compression. Compression thickens the crust as materials are squeezed. D. strike-slip faults Correct Both right-lateral and left-lateral strike-slip faults help those parts of Asia move. E. -The Indian Plate is too thick. -The Indian Plate is too buoyant. Correct The Indian Plate is a continental plate and has a low density. Because it is a continental plate, the Indian Plate is too thick to slide beneath another plate easily.
A. Which of the following best describes the difference between differential stress and confining pressure? B. Which of the following describes the orientation of the long axes of rocks and mineral grains in relationship to the stress applied? Choose all that apply. C. See card 7 D. See card 8
A. In differential stress, the stresses on the sides are greater than the force of gravity. Stresses are the same on all sides for confining pressure. B-The long axis of a rock is parallel to the direction of the weakest stress applied. -Mineral grains are oriented parallel to the direction of the weakest stress applied. C. See card 7 D. See card 8
Part A - Deciphering the Geologic History of the Grand Canyon Examine the images of the Grand Canyon below. Notice that most of the canyon consists of layers of sedimentary rocks, but if you were to hike down into the inner gorge you would encounter the Vishnu Schist, a metamorphic rock. Which of the following processes were involved as the Vishnu Schist metamorphosed? Part B - Geological Events in the Grand Canyon What does the Vishnu Schist tell you about the history of the Grand Canyon prior to the formation of the canyon itself? What is the order of events in the Grand Canyon? Place the following events in the order in which they happened. Rank from oldest to most recent events. Part C - Vishnu Schist at the Grand Canyon Which of the following best describes why the Vishnu Schist is visible at Earth's surface? Part D - Metamorphic Rock Where else might you expect to find metamorphic rocks like the Vishnu Schist of the Grand Canyon?
A. Intense pressure due to regional metamorphism. Correct You have correctly identified the origin of the Vishnu Schist. B. OLDEST EVENT: -formation of Vishnu Schist -Deposition of sedimentary layers found above the Vishnu Schist -Carving of the canyon by the Colorado River :MOST RECENT EVENT Correct You have correctly identified the sequence of events in the Grand Canyon. Correct You have correctly identified the sequence of events in the Grand Canyon. C. The Vishnu Schist was exposed when sedimentary layers above it were eroded. Correct You have correctly identified the reason why the Vishnu Schist is found at Earth's surface. D. -Deep beneath Earth's surface, where sedimentary layers have been buried. -In a mountain range. Correct Congratulations, you have successfully completed the exercise. You should have a better understanding of the Vishnu Schist in the Grand Canyon, and the processes that led to its formation.
A. How are metamorphic rocks formed? B. Do metamorphic rocks look like the preexisting rock from which they form? C. What is foliation? D. How will foliation in continental metamorphic rocks formed during subduction be oriented? E. What would you call a granite that has undergone metamorphism and now exhibits foliation?
A. Preexisting rock is altered through heat and pressure. B. sometimes, but not always C. banding in metamorphic rocks that results from the reorientation of minerals D. perpendicular to the direction of plate movement E. gneiss
Part A Which of the following statements about relative and absolute age dating is most accurate? Part B What is the principle of original horizontality? Part C What is the principle of superposition? Part D What is the principle of cross-cutting relationships? Part E Five layers of rock are cut by two faults. Both faults cut through all five layers of rock. Fault A breaks through to the surface, whereas fault B does not. Which of the following statements about faults A and B is most accurate? Part F Which principle of relative age dating is important for determining the relative age of igneous rock that has intruded into overlying rock? Part G A fault (F) breaks three layers of sedimentary rock (S). An igneous intrusion (I1) has broken through the bottommost layer of rock. A second igneous intrusion (I2) has moved up the fault and pooled on top of the uppermost layer of rock. Which event would be considered the youngest?
A. Relative age dating places rocks and events in chronological order but does not provide information about absolute age. B. Sedimentary rocks are close to horizontal when deposited. C. Within a sequence of rock layers formed at Earth's surface, rock layers lower in the sequence are older. D. Geologic features that cut through rocks must form after the rocks that they cut through. E. Fault A is younger than fault B, and both are younger than the five layers of rock. F. the principle of cross-cutting relationships G. The intrusion of I1 or I2 is the youngest event. Without more information, we cannot know which igneous rock is youngest.
ITEM 1-15-A & B Part A Which of the following statements best describes the orientation of rock layers for a structural dome or structural basin? Part B If strike and dips symbols were placed on a map of a basin, which way would the dips point? C. SEE CARD 46 D. SEE CARD 47
A. Rock layers wrap around a single point. Correct Domes and basins are round and will fold in all directions around a central point. B. Dips point down toward the center. Correct Basins are similar in shape to a bowl, where the lowest point is in the center. C. SEE CARD 46 D. SEE CARD 47
ITEM 1-13-A Part A - Geologic History of the Split Mountain Anticline Below is an image showing part of the Split Mountain Anticline of Dinosaur National Monument, Utah. It is quite large, so we are looking at only a small portion of the anticline's southern flank. In this photo, you can see sedimentary rocks that have been exposed by weathering and erosion. Yellow lines show curved light-colored sandstone beds that are exposed in canyons cut into the anticline. Orange lines point out red- to orange-colored dipping sedimentary beds that have been eroded from the upper part of the anticline. Concentrate on the series of events that led to the formation and exposure of this anticline. Rank the following events in order from OLDEST to YOUNGEST in age.
A. SEE IMAGE *Correct Sediments were deposited in horizontal layers, and then buried and lithified to form sedimentary rocks. When these rocks were subjected to compressional forces, they deformed in a ductile manner by bending into an anticline. With time, the folded layers became exposed from processes of weathering and erosion. B. SEE CARD 40 C. SEE CARD 41
ITEM 1-18-A Part A Which image is an example of an angular unconformity? SEE IMAGE FOR ANSWER SELECTIONS.
A. SEE IMAGE B-E ON CARDS #88-91
ITEM 1-10-A Part A - Relative dating The following diagram depicts a map area and the underlying geology. Rock layers are approximately parallel to the ground surface. The rock types of the layers are labeled. Dikes (lineations) and faults (tubular features) cut through the rock layers vertically. Use the relative dating principles described in the introduction to reconstruct the geologic history of the area depicted in the diagram. Drag and drop the correct descriptions for the order of events conveyed in the accompanying diagram. Drag the appropriate labels to their respective targets. Note that not all labels will be used.
A. SEE IMAGE Correct Relative dating is useful when exact numerical dates are not needed to determine the age of rocks in an area. The conglomerate layer was deposited after Fault A and the limestone layer is older than the sandstone layer. Fault A is younger than sandstone, but older than the conglomerate. Dike A is younger than the sandstone, conglomerate, limestone, and shale. Dike B is younger than the batholith and fault B, but older than Dike A.
ITEM 1-3-PART A Geologists use the term stress to describe forces that are applied to an area of rock. When stress is applied unequally in different directions, it is termed differential stress. There are three types of differential stress: Compressional stress: Forces push a body of rock inward, resulting in compression of the body. Tensional stress: Forces pull a body of rock outward, resulting in elongation of the body. Shear stress: Opposing forces push different ends of a body of rock in opposite directions, resulting in displacement of one end of the body with respect to the other. Rocks first respond to stress by deforming elastically, but if their elastic limit is surpassed, then they will deform by ductile flow (ductile deformation) or they fracture (brittle deformation). Elastic deformation: The rock will return to nearly its original size and shape when the stress is removed. Ductile deformation: This is a type of solid state flow that produces a change in the size and shape of a rock body without fracturing. It occurs at depths where temperatures and confining pressures are high. Brittle deformation: This involves the fracturing of rock and is associated with rocks near the surface. These deformations can result in the formation of several different geologic structures, such as: Folds: Ductile deformations where a bent rock layer or series of layers that were originally horizontal are subsequently deformed. Faults: Brittle deformations (fractures) in a rock mass along which movement has occurred. Joints: Brittle deformations (fractures) in a rock along which there has been no movement. There are three categories of faults—compressional, tensional, and translational—matching up perfectly to the types of stresses that cause them. Compression usually results in the shortening of rock bodies, which may cause a rock mass to thrust over another. Tension results in the lengthening of a rock mass. For example, a slab of rock could pull apart from another and slide downward with respect to the other slab, which will result in a normal fault. Finally, shear stress usually causes rock bodies to laterally slide past each other. A. Determine whether each geologic feature is being caused by tensional, compressional, or shear stresses by analyzing the directions of the forces being applied. Drag the appropriate items to their respective bins. Each item may be used only once. B. See card 28
A. See image B. See card 28
ITEM 1-14-C Part C Which fold orientation is visible in Figure 2?
C. overturned Correct Note how the limbs are dipping in the same direction, but at different angles
Part A Which of the following orogenies helped to create the Appalachian Mountains? Part B Which event marked the creation of the supercontinent Pangaea? Part C Which of the Appalachian Mountain Belt Provinces are visible in the circled area of Figure 1? Part D Which of the following geographic provinces is the newest addition to the North American continent?
A. Taconic, Acadian, and Alleghanian Correct The Appalachians were built in three pulses over the course of nearly 200 million years. B. The Iapetus Ocean closed during the Alleghanian Orogeny. Correct The Alleghanian Orogeny was the last of three orogenies that created the Appalachians when Pangaea formed. C. Valley and Ridge SEE IMAGE Correct The Valley and Ridge Province is famous for its sinuous ridges and valleys, particularly in Pennsylvania. D. Coastal Plain Correct The Coastal Plain consists of a blanket of sediments that have been deposited since the opening of the Atlantic.
A. What role does hot ion-rich water play in the process of metamorphism? B. By what process did the gabbro turn into amphibolite? C. What is a mantle plume? D. What kind of metamorphic texture results in the segregation of light and dark mineral bands? E. Why are garnets used in sandpaper?
A. Water migrates into host rock carrying ions to stable minerals in order to facilitate growth of new metamorphic minerals. B. The gabbro was heated to 500 °C and buried a few miles below the Earth's surface. C. hot mantle rock rising from deep within the Earth D. gneissic texture E. Garnets have a value of 8 or 9 on the Mohs Hardness Scale, making them very abrasive.
ITEM 1-20-A, B, C, & D Part A A terrane is __________. Part B Which tectonic boundary is associated with the addition of terranes to a continent? Part C What is the name of the process by which terranes are added to continents? Part D Using the map in Figure 1, determine which of the named terranes accreted earliest to North America. Part E SEE CARD 54
A. a mass of rock that formed elsewhere and was added to a continent Correct Terranes are added to continents where subduction zones develop. B. convergent boundary Correct Terranes are added to a continent through subduction. C. accretion Correct Accretion occurs as a result of a subducting plate. D. Yukon-Tanana SEE IMAGE Correct The Yukon-Tanana Terrane was accreted sometime during the Paleozoic Era. E. SEE CARD 51
Part A Which of the following includes all common types of radioactive decay? Part B Which of the following statements regarding radioactive decay is true? Part C If one half-life has lapsed, what is the radioactive parent to stable daughter isotope ratio? Part D Radioactive decay in mineral shows that two half-lives have elapsed, giving an age of approximately 1.4 billion years. Using the table in the video as a reference, what is the correct radioactive parent and stable daughter isotope pair?
A. alpha particle emission, beta particle emission, electron capture B. More daughter products accumulate over time. C. 50:50 D. U235, Pb207 EXAMPLE OF HALF LIFE EQUATION IN IMAGE:
ITEM 1-14-A&B A. Which type of fold has rocks folding up in the middle? B. Which of the following terms best describes the orientation of the fold in Figure 1? C. SEE CARD 43 D. SEE CARD 44
A. anticline *Correct Anticlines are also known as upfolds. B. symmetrical SEE IMAGE *Correct The limbs both dip downward at the same angle, but in different directions. C. SEE CARD 43 D. SEE CARD 44
A. Which type of force causes folding? B. What is an anticline? C. What is a syncline? D. Imagine an anticline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface? E. Imagine a syncline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface? F. What produces plunging folds? G. What does the term plunging fold mean? H. Imagine a fold has been eroded to a flat surface. In general, how would you know whether this fold is plunging?
A. compressional force B. a fold shaped like an upside-down U C. a fold shaped like a right-side-up U D. Rocks would be youngest on the edges and oldest in the middle. E. Rocks would be oldest on the edges and youngest in the middle. F. a combination of folding and tilting G. a fold that is tilted down into Earth H. Nonplunging folds look like straight lines at the surface, and plunging folds look like wavy lines.
Part A Following the deposition of a sequence of sedimentary rocks, which event is the first to occur to produce an angular unconformity? Part B A(n) __________ exhibits sedimentary layers that are parallel to each other above and below an erosive surface. Part C Which of the following is an accurate description of a nonconformity? Part D The sedimentary layers above an erosive surface are __________ relative to all rocks present below the surface. Part E Which of the following is a common feature that all unconformities exhibit?
A. deformation B. disconformity C. younger sedimentary strata overlie uplifted and weathered igneous or metamorphic rocks D. younger E. erosive surface
How did the North American Cordillera form?
A. from the collision of several island arcs with the west coast of North America
Part A A sandstone contains inclusions of metamorphic rock. An igneous dike cuts both the sandstone and inclusions. List the rocks from youngest to oldest. Part B If a sequence of sedimentary units is cut by a fault, what does the principle of cross-cutting relationships tell a geologist? Part C Which of the following describes the principle of original horizontality? Part D An undeformed sequence of sedimentary rocks is exposed in a large river canyon. Which two principles would be demonstrated by the rocks? Part E An igneous dike cuts through limestone, but not through the overlying sandstone. Which of the following statements is most accurate?
A. igneous dike, sandstone, metamorphic rock B. All of the sedimentary units must have been deposited and lithified before being cut by the fault. C. Folded sedimentary layers were originally laid down flat and later deformed. D. principles of superposition and lateral continuity E. First, the limestone was laid down, then intruded by the igneous dike, and lastly the sandstone was deposited.
Part A What is the hinge line of a fold? Part B What is the orientation of a fold's hinge line with respect to the orientation of plunge? Part C How will the orientation of a plunging anticline's limbs change in the direction the fold is plunging? Part D What kind of fold is circled in Figure 1?
A. line of maximum inflection that layers wrap around Correct The hinge line is the location of greatest flexure in the rock layers. B. Hinge line is in the direction of plunge. Correct The direction of plunge is determined by the direction the hinge line descends into the Earth. C. They will close to a point. Correct Plunging anticlines close to a point, making an arrow in the direction of plunge D. nonplunging syncline *SEE IMAGE Correct Nonplunging synclines will have limbs that point down toward the center of the fold and will produce a pattern of broad stripes at the surface.
Part A Which fault will see the hanging wall move down relative to the footwall? Part B What kind of fault is visible in Figure 1? SEE IMAGE Part C What kind of force would create the fault in Figure 1? SEE IMAGE Part D __________ faults combine elements of strike-slip and dip-slip motions.
A. normal fault Correct Normal faults are created by tension, which will pull the landscape apart. B. reverse fault Correct Reverse faults are created when the hanging wall moves up relative to the footwall. C. compression Correct Compressional force creates reverse and thrust faults D. Oblique-slip Correct Oblique-slip movements will pull blocks apart as well slide them past each other.
Part A A _____ is formed when magma intrudes between existing sedimentary layers. Part B If a limestone, a shale, and a sandstone are deposited in that order without interruption, which of the following is true? Part C What scenario requires a geologist to use the principle of cross-cutting relationships? Part D Which of the following is associated with an erosive surface? Part E An igneous dike cuts across existing sedimentary layers and erupts at the surface, creating a layer of basalt. The basalt, as well as all the layers below, are then cut by a fault. Which statement is true?
A. sill B. The limestone is the oldest and the succession is conformable. C. A dike truncates layers in a sedimentary succession. D. a stream running across an irregular surface E. The fault is the youngest because it cuts through all the sedimentary layers and basalt.
Part A Which of the following scenarios could result in the development of a compressional mountain belt? Part B Which geologic features would be present in compressional mountain belts? (Note: There may be more than one answer.) Part C Which of the following rocks are characteristic of compressional mountain building? Part D Using the map provided in Figure 1, in which province would the Rocky Mountains of the United States be located?
A. two landmasses collide Correct When two landmasses collide, such as at a convergent boundary, the edges will fold and buckle to create mountains. B. folds intrusive igneous rocks thrust faults Correct Partial melting creates magma, which is emplaced near the plate boundary. Rocks that are compressed become "wrinkled." Thrust faults result from compressional force. C. schist Correct Metamorphic schist forms in high-pressure environments such as subduction zones. D. young mountain belts SEE IMAGE Correct The uplift of the Rocky Mountains occurred approximately sixty million years ago.
Part A Batholiths, such as those that make up the Sierra Nevada Mountains of California, form at great depth in the crust. How could they have been exposed at the surface? Part B _____ is the principle that explains why materials uplift to a certain elevation. Part C Using what you know about isostasy, how would the crust behave if a large glacier were removed? Part D If the Rocky Mountains were eroded, what would happen to the roots of the mountains?
A. uplift and erosion Correct The batholiths would have been uplifted as the continent rose and exposed through erosion. B. Isostasy C. The crust would move up in elevation. Correct The crust will bounce back after glaciation just like it would if large mountains would erode. D. The roots would rebound upward. Correct The crust will uplift as weight is removed, which will also make the roots move upward.
ITEM 1-13-PART B Part B - Folds of Calico Ghost Town The parking lot of Calico Ghost Town in southern California is a great place to study folds due to excellent exposure and easy access. The series of questions below focuses on types of folds and their components. The photo below shows a fold train, composed of two folds, and their features outlined by orange and red lines. Drag the appropriate labels to their respective targets. Not all labels will be used. A. SEE CARD 39 C. SEE CARD 41
B. SEE IMAGE *Correct The photo shows a fold train consisting of an anticline on the left and a syncline on the right. The orange lines delineate a limb shared by both the anticline and adjacent syncline. The red line represents the axial plane, which divides the syncline symmetrically. A. SEE CARD 39 C. SEE CARD 41
ITEM 1-10-B Part B - Interpreting inclusions Part complete Fragments of rock can be separated from its parent layer, and be relocated into another layer. Inclusions are rock fragments that are relocated into another layer. Interpreting inclusions are another relative dating technique. The principle of inclusions is described below. Rock fragments included within another rock must be older than the rock in which they are included. For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves. However, in contrast, if magma intrudes into surrounding host rock, the latter is older, as are any inclusions of the host rock found in the intrusion. The following illustration depicts an area and its underlying geology. Three points in time are depicted. Time A: An igneous rock exists underground. Time B: The ground surface is eroded, which exposes the igneous rock. Time C: Layers of sedimentary rock are formed atop of the igneous rock. Using the principle of inclusions, rank the labeled areas from oldest to youngest. Rank from oldest to youngest.
B. SEE IMAGE OLDEST C A B D YOUNGEST Correct C is the oldest area, followed by A and B. D is the youngest area.
ITEM 1-10-C Part C - Principles of relative dating Part complete The sentences below describe different techniques involved in relative dating. Complete the sentences using the following phrases. First, you can refresh your memory by revisiting the principles of relative dating: Principle of superposition: When comparing two sedimentary rock layers, the bottom layer must be older than the layer above it. The logic is a lower layer must already exist for another layer to be deposited on it. Principle of original horizontality: Sedimentary rocks were originally deposited as flat-lying, horizontal layers. If a layer is tilted, it must have moved. Principle of cross-cutting relationships: Any rock or feature, cutting through another rock or feature, must be younger than the material through which it cuts. Match the words in the left column to the appropriate blanks in the sentences on the right.
C. 1. Applying the principle of original horizontality indicates that layers were repositioned from a flat-lying orientation. 2. Magma intrudes into layers of sedimentary rock and displaces them. We can deduce that the intruded magma that crystallizes is younger than the surrounding sedimentary layers by applying the principle of crosscutting relationships. 3. While visiting the Grand Canyon, you are amazed by the depth of layers of sedimentary rock before you - the principle of superposition is evident here where progressively younger layers have formed over time and are stacked upon each other. 4. A fault cuts through layers of limestone, sandstone, and conglomerate. The surrounding layers must be older than the fault. 5. A mass of granite has inclusions of surrounding sandstone. The sandstone and surrounding layers show evidence of uplift over time. The granite must be younger than the sand deposits. Correct Applying the principle of original horizontally shows that layers have been disturbed during deposition from their original source area. Magma intrudes into layers of sedimentary rock and displaces them. We can deduce that the intruded magma that crystallizes is younger than the surrounding sedimentary layers by applying the principle of crosscutting relationships. While visiting the Grand Canyon, you are amazed by the depth of layers of sedimentary rock before you. The principle of superposition is evident here where layers have deposited over time and are stacked upon each other. A dike cuts through layers of limestone, sandstone, and conglomerate, and a fault passes through these layers as well. The surrounding layers must be older than the dike and the fault. A mass of granite has inclusions of surrounding sandstone. The sandstone and surrounding layers show evidence of uplift over time. The granite must be younger than the sand deposits.
ITEM 1-13-PART C Part C - A Limb of the Uinta Anticline The photo below shows dipping sedimentary beds exposed along a limb of the Uinta Anticline in northeast Utah. The axial plane of the fold is located to the left of this exposure, and not shown in this photo. The red layers in the center of the photo are predominantly sandstones, whereas the lighter-colored rocks that make up the ridge to the right are carbonates. You can see that most of these layers are dipping to the right. Imagine you are out in the field and have to sketch and label the view below. Based on observations from the previous photo, which of the following sketches is the most accurate? A. SEE CARD 39 B. SEE CARD 40
C. SEE IMAGE Correct Sketch #5 correctly outlines the orientation of the dipping beds, as well as the rock types that were discussed in the text. The older units are the red sandstones exposed in the middle part of the photo, while the younger are the carbonates located to the right. A. SEE CARD 39 B. SEE CARD 40
ITEM 1-6 C. Part C - Labeling stresses in relation to a metamorphic rock The figure below shows a metaconglomerate. Place the thick arrows in the direction of maximum stress and the thin arrows in the direction of minimum stress. If stress from all directions is equal, place all thin arrows. Drag the appropriate labels to their respective targets. Labels may be used only once.
C. See image
ITEM 1-18-C Part C What does the term unconformity mean?
C. a missing rock layer in a sequence that represents a period of erosion or nondeposition
ITEM 1-15-C Part C Based on the ages of the rock layers in the cross-section, what kind of fold is in Figure 1? (Note: In map view, this feature would have a bull's-eye pattern.)
C. basin Correct Basins have the youngest rocks in the center and the oldest on the outside.
Part A - Types of dip-slip faults Sort the following features and descriptions according to the two dip-slip faults shown. Drag the appropriate items to their respective bins.
Correct You have considered the different types of dip-slip faults. Reverse and thrust faults are caused by compressional forces, whereas normal faults are caused by extensional forces. This knowledge is important to understanding how mountain belts are formed and how folds are created.
ITEM 1-18-D Part D What characteristic most directly DISTINGUISHES an angular unconformity from a nonconformity?
D. Angular unconformities separate rock layers along nonparallel surfaces.
ITEM 1-6 D. Part D - Labeling stresses in relation to a metamorphic rock Part complete The figure below shows a metaconglomerate. Place the thick arrows in the direction of maximum stress and the thin arrows in the direction of minimum stress. If stress from all directions is equal, place all thin arrows. Drag the appropriate labels to their respective targets. Labels may be used only once
D. See image
ITEM 1-15-D Part D What kind of structure is present in Figure 2?
D. dome Correct Domes are round structures that arch upward.
ITEM 1-14-D Part D Which kind of fold is visible in Figure 3?
D. syncline Correct Synclines are smile-shaped folds also called downfolds
ITEM 1-20-E Part E The map in Figure 2 is a cross-section of the North American continent 600 million years ago and after the break-up of Pangaea approximately 200 million years ago. Which material(s) had been accreted to North America as terranes?
E. Iapetus Ocean Island Arc and sediments, the Avalon Terrane, and a remnant of Africa SEE IMAGE Correct All of these landmasses stuck to North America and increased its size.
ITEM 1-18-E Part E Which list best describes the events that would lead to the layering of sedimentary rocks in this diagram?
E. deposition, erosion, deposition, erosion, deposition
________ is a strong, parallel alignment of coarse mica flakes and/or of different mineral bands in a metamorphic rock.
Foliation
Geologists have divided the whole of history into units of increasing magnitude. This is called the geologic time scale. The entire time scale was originally based on relative dating, since radiometric dating was not available at the time. Absolute dating techniques determine a numerical age of strata given in number of years. Relative dating techniques, on the other hand, determine the age of a stratum relative to other strata (i.e., if it is younger or older), without providing any numerical data. Geologists have been able to determine the relative ages of rocks and any fossils they contain to reconstruct a history that reveals the evolution of Earth's continents and living organisms using four principles of stratigraphy: Principle of Superposition: Younger strata are deposited on top of older strata. Principle of Original Horizontality: Strata are deposited horizontally. Tilted strata had been tilted by some geologic event after the time of deposition. Principle of Lateral Continuity: Layers of sediment initially extend laterally in all directions. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous. Principle of Cross-Cutting Relationships: Magma intrudes and crystallizes (forming features such as faults and dikes). These features are younger than the strata they cut through because the strata they cut through must have been there before the intrusion of magma.
NOT A QUESTION
ITEM 1-10 Geologists study the natural history of an area by investigating outcrops, which are rock formations exposed aboveground. Determining the age of outcrop layers is an important step in interpreting the area's geologic history. Methods to date the layers fall into two categories: Absolute dating methods, such as radiometric dating, provide the age of layers with values such as number of years. However, suitable material to date is not always present. Relative dating determine the sequence of events relative to each other. For example, the age of a fault can be determined to be younger or older than certain layers, although the age in years of the fault or layers will not be determined. Relative dating is applied to outcrops by using the following principles: Principle of superposition: When comparing two sedimentary rock layers, the bottom layer must be older than the layer above it. The logic is a lower layer must already exist for another layer to be deposited on it. Principle of original horizontality: Sedimentary rocks were originally deposited as flat-lying, horizontal layers. If a layer is tilted, it must have moved. Principle of cross-cutting relationships: Any rock or feature, cutting through another rock or feature, must be younger than the material through which it cuts. The list below provides examples where rock must be present prior to the secondary features (e.g., fault) to cut through: Faults: a planar break in rock layers that caused relative mass movement Dikes: igneous intrusions that cut vertically through rock layers Sills: igneous intrusions that are parallel to rock layers Throughout this exercise, you will explore how these principles are applied to explore the history of several geologic landscapes.
NOT A QUESTION
Which of the following metamorphic rocks are foliated? Choose all that apply.
Phyllite Gneiss
Which of the following best describes the conditions of contact metamorphism?
Pressures are fairly low, the rock is in the upper part of the crust, and heat is supplied from a nearby magma body.
Which of the following metamorphic rocks are nonfoliated? Choose all that apply.
Quartz anthracite
ITEM 1-8-A Part A - Basic Principles for Relative Geologic Dating Below is a geologic structure that illustrates the various principles of relative dating. You will identify the basic principles used in relative geologic dating by dragging labels to their corresponding targets in the image below. Drag the appropriate labels to their respective targets.
SEE IMAGE Correct As you can see from above, we can determine a sequence of events using the logic of these principles when observing sedimentary rock.
ITEM 1-8-B Part B - Ordering of Geologic Events The principles of relative dating can be used to understand the order of geologic events. A geologic event can be anything: the deposition of horizontal layers of sedimentary rock, the faulting or folding of rock layers, the tilting of rock layers, the erosion (or wearing away) of rock, the intrusion of volcanic rock within existing rock layers, and so on. Refer to these relative dating principles: Inclusions: Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.) The Principle of Cross-cutting Relationships: Any rock or feature cutting through another rock or feature must be younger than the material through which it cuts. (For example, with faults, the first rock must be there for these secondary features, such as igneous intrustions like dikes or fractures, to cut through.) Tilting or deformation could occur to an otherwise horizontally layered sedimentary rock. Most layers of sediment are deposited in a nearly horizontal position. Thus, when we see rock layers that are folded or tilted, we can assume that they must have been moved into that position by crustal disturbances after their deposition. In such an instance, the tilted structure will be younger than the orginal horizontal layers. Order the four images below along the timeline based on the sequence of geologic events. Rank from oldest to youngest.
SEE IMAGE Correct You can apply the logic of the principles of relative dating to successfully sequence the order of geologic events in a scene. These principles allow you to tell the geologic story of a landscape.
ITEM 1-6-A Part A - Principles of Stratigraphy The figure below shows a series of rock layers and a volcanic dike. Rock A is the oldest rock in the sequence. Use the principles of stratigraphy to rank items A-F. Rank the strata from oldest to youngest.
SEE IMAGE OLDEST A D C B F E YOUNGEST Correct Notice that the tilted strata are immediately overlain by horizontal strata. This can only occur if erosion has partially removed the tilted strata so they all terminate at the same depth.
In a reverse fault, the hanging wall block moves up relative to the footwall block.
True
A thrust fault is best described as ________.
a low-angle, reverse fault
Where do Andean-type mountain belts typically form?
along a subduction zone
Which type of plate boundary is most associated with Earth's major mountain chains?
convergent plate boundaries
Which process can decrease the height of a mountain?
gravitational collapse
Which type of metamorphism is found at a divergent plate boundary?
hydrothermal metamorphism
Part A What fundamental concept states that in a horizontal sequence of conformable sedimentary strata, each higher bed is younger than the bed below it?
law of superposition
Word Analysis. Examine the words and/or phrases for each question below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.
marble
An unconformity is a buried ________.
surface of erosion separating younger strata above from older strata below
Tensional forces normally cause which one of the following?
normal faults
Which geological principle states that even if most sedimentary rock layers are presently folded, they were deformed after deposition?
principle of original horizontality
