(1) Sketch a cross-section
of typical ocean crust and label the four basic layer types.
How do we know that this is the structure
of the ocean crust (two main pieces of evidence).
(2) Sketch a cross-section
of a mid-ocean ridge system and explain how it can produce the ocean crust.
We know that the plate consists of
crust and mantle lithosphere. How is the oceanic mantle lithosphere produced?
(3) How does water behave within ocean crust near mid-ocean ridges?
(4) What is the relationship between the depth of the ocean at some point and the age of the sea floor at that point? Why?
(5) What force causes the plates to spread at the mid-ocean ridge.
(6) Why does Bouguer gravity typically show negative anomalies over oceanic or continental rifts?
(7) What is the difference between passive and active continental rifts.
(8) What is the relationship between continent rift and oceanic rifts?
(9) In addition to the volcanoes, why are there mountains and high topography along the edges of continental rifts.
(10) What are normal faults and how do they help to explain tilted crustal blocks that are commonly seen in rifts?
(11) Sketch a map
view of an oceanic transform fault and show why the fault is only active between
the ridge segments.
Using your sketch explain the difference
between oceanic transform faults and oceanic fracture systems.
{Recall the difference between
fractures and faults.}
(12) Why are spreading ridges offset by so many transform faults?
(13) Describe
the plate tectonic situation in New Zealand? Where are the subduction
zones and how does the
Alpine fault fit in?
(14) Has the west coast of California always had a major strike-slip, "transform" fault. If not, how did it get started?
(15) Show with sketches how you can get pressure ridges and sag ponds along a strike-slip fault.
(16) What are confinng and releasing bends? Why aren't maure transform faults straight?
(17) How can offset stream valleys be used to determine the rate of fault movement?
(18) Some mountains
along strike-slip faults (continental transform faults) are interpreted to be
flower structures.
What is a flower structure
and how do they develop?
(19) What are 3
different ways to measure rate of slip along transform faults? Why do different
methods of measuring
slip rate along the San Andreas
fault give different estimates?
1) The largest single component of the lithosphere is the A) oceanic crust. B) continental crust. C) uppermost mantle. D) low velocity zone. E) Moho.
2) Ophiolites consist of A) sediment. B) pillow basalts. C) basalt dikes. D) gabbro. E) all of the above
3) The main topographic feature of a mid-ocean ridge is the A) rounded profile. B) black smoker. C) central graben. D) volcanism. E) regional uplift.
4) Ophiolite sequences are underlain by A) basalt flows. B) peridotite. C) organic sediment. D) sheeted dikes. E) all of the above
5) Sheeted dike complexes are A) vertically oriented intrusions. B) horizontally layered volcanic flows. C) found beneath the gabbro layer in ophiolites. D) extruded onto the ocean floor at mid-ocean ridges. E) mineral deposits near hydrothermal vents in the seafloor.
6) The thickness of the oceanic crust is about __________ km; that of the oceanic lithosphere is about __________ km. A) 50; 50 B) 70; 130 C) 7; 420 D) 10; 70 E) 7; 100
7) The low-velocity zone (LVZ) is A) gabbro in composition. B) about 80% melted. C) the lowermost lithosphere. D) the uppermost mantle. E) all of the above
8) Ocean floor magnetic stripes originate in the A) peridotite. B) pillow basalts. C) sheeted dike complex. D) black smokers. E) sedimentary covers.
9) The major mechanism for dissipation of Earth's internal heat is A) volcanism. B) mantle cooling. C) circulating sea water. D) vent organisms. E) atmospheric radiation.
10) Metal cations leached from the sea floor by hydrothermal activity include A) Ca, Cu, Zn. B) Si, Fe, S. C) Mn, Si, Zn. D) Na, Cu, Ca. E) all of the above
11) Sea floor basalt altered by hydrothermal Ca ¹ Na exchange is called A) harzburgite. B) gabbro. C) pillow basalt. D) andesite. E) spilite.
12) All ocean ridges have the same topographic profile when depth is plotted against A) change in slope. B) rock age. C) spreading rate. D) rock type. E) ocean temperature. 1
3) Geologic structures responsible for rotated sedimentary blocks in rift valleys are A) listric faults. B) shoulder uplift. C) rift-boundary faults. D) grid faults. E) all of the above
14) Along continental rift axes, the crust lies directly upon A) ancient sediments. B) ophiolite. C) peridotite. D) gabbro. E) asthenosphere.
15) The best example of an active Cenozoic rift would be the A) Rio Grande. B) East African. C) Baikal. D) Rhinegraben. E) Death Valley.
16) An example of a diverging plate boundary is A) the Mid-Atlantic Ridge. B) the San Andreas fault. C) the Zagros Mountains (Iran). D) the Appalachian Mountains. E) the Himalaya Mountains.
17) Passive continental margins originate as A) continental shelves. B) oceanic lithosphere. C) continental rift shoulders. D) trenches. E) orogens.
18) Passive continental margins typically have these evidences of deformation. A) volcanoes B) earthquakes C) normal-faulted basins D) strike-slip faults E) all of the above
19) Continental margins subside and submerge due to A) mafic dike intrusion. B) sediment loading. C) loss of heat. D) sea level changes. E) all of the above
20) The major clue to the existence of an ancient buried aulacogen would be A) topography. B) volcanism. C) Bouguer gravity anomalies. D) high heat flow. E) all of the above
21) Passive continental rifts can be controlled by A) remote subduction. B) mantle upwelling. C) hot spot activity. D) thickened asthenosphere. E) transform faults.
22) The conjunction of the Red Sea, Gulf of Aden, and East African Rift is a (an) __________ triple junction A) RTR B) TRT C) RRR D) RFF E) RRF
23) The shape of a continental rift graben is controlled by A) extension. B) intrusion. C) volcanism. D) erosion. E) all of the above
24) Iceland is A) a volcanic arc on a subduction zone. B) not tectonically active. C) part of the mid-oceanic ridge. D) a transform fault scarp. E) a displaced terrane.
25) Mid-oceanic ridges stand high above the surrounding sea floors because they A) are made of rhyolite. B) are hotter than surrounding rocks. C) have higher density than surrounding rocks in the seafloor. D) are underlain by a mass of lower density sediment. E) are underlain by low-density granite.
26) Oceanic crust A) becomes progressively younger away from the mid-ocean ridges. B) becomes progressively older away from the mid-ocean ridges. C) is the same age virtually everywhere. D) is always less dense than continental crust. E) is composed of andesite.
27) The last stage in development of an aulacogen is A) intrusion. B) doming. C) growth of mantle plume. D) rifting. E) subsidence.
28) Failed rifts are thus named because A) they never really created fractures in the crust. B) they formed in oceanic crust instead of continental crust. C) they never developed into ocean basins. D) they are actually transform faults. E) they result in tectonic uplift only.
29) Which area is now undergoing continental rifting? A) Iran B) Iceland C) east Africa D) south Florida E) Greenland
30) Transform margins are characterized by A) high seismic activity. B) shallow hypocenters. C) lack of magmatic activity. D) shear stress. E) all of the above
31) Which of the following is NOT true of transform boundaries? A) horizontal offset B) substantial offset C) vertical dip D) deep hypocenters E) extend to the Moho
32) Which surface feature would NOT be observed along the San Andreas Fault? A) shutter ridges B) offset stream channels C) springs D) sag ponds E) chain of cinder cones
33) An example of a transform plate boundary within North America is A) Aleutians. B) San Andreas fault. C) Baja California. D) Appalachians. E) Hawaii.
34) A releasing bend in a strike-slip fault zone may generate A) migmatites. B) subsidence. C) increased erosion. D) intense compression. E) rapid uplift.
35) Pull-apart basins on transform boundaries may produce A) folding. B) volcanic activity. C) secondary thrusts. D) normal faults. E) all of the above
36) Extensional duplexes form A) fault-bounded basins. B) uplift. C) subduction. D) in a transpressive setting. E) all of the above
37) Fracture zones are A) igneous contact zones. B) topographic scars. C) relative plate motion indicators. D) aseismic. E) all of the above
38) Plates that contain a continent move more rapidly than do strictly oceanic plates.
39) The uppermost mantle makes up 50 ¹ 75% of the lithosphere.
40) Almost all oceanic rifts begin as continental rifts.
41) The continental lithosphere appears to be more resistant to rifting that the oceanic lithosphere.
42) Continental rifting and collisions began about 200 million years ago.
43) Topographic similarity between oceanic and continental rifts indicates that similar processes are operating each.
44) Oceanic rifts separate about 10 times faster than continental rifts.
45) The marine sediments of a passive continental margin are always older than igneous rocks in adjacent oceanic crust..
46) Passive margin rift basins have poor preservation potential for sediments..
47) Central grabens are characteristic of fast-spreading ridges.
48) Ophiolite sequences are only known from deep-sea drilling records.
49) Decompressing mantle peridotite melts to release liquid basalt.
50) Oceanic ridge sediments are thickest in the central graben.
51) In the low velocity zone under a mid-ocean ridge, the geotherm crosses the mantle solidus.
52) Spreading ridge animal communities depend upon chemosynthesis, not photosynthesis.
53) Circulating sea water adds sodium chloride to ocean floor basalts.
54) Slow-spreading ridges have steep, abrupt sides.
55) Sea floor topographic irregularities are isostatically compensated.
56) The East Pacific Rise is spreading about ten times as the Mid Atlantic Ridge.
57) The direction of sea floor spreading is fixed by the original orientation of the continental rift.
58) Changes in rift direction and length cause magnetic stripe patterns to converge.
59) Mid-ocean rifts are the surface expression of upwelling mantle convection.
60) Ridge crests average 3 km higher than older, cooled ocean floor.
61) Ridge push arises primarily from the ridge's higher elevation.
62) Continental rift graben fault scarps maintain dips of about 60e.
63) Continental rift bounding faults provide avenues for magma to rise to the surface.
64) Continental rift volcanism is almost exclusively basaltic.
65) Passive rifts will show smaller Bouguer gravity anomalies than active ones.
66) Rift volcanism occurs both along fissures and at central volcanoes.
67) Africa is being pulled apart by surrounding subduction zones.
68) The asthenosphere appears to be more mobile under continents than under oceans.
69) The most prominent characteristic of transform margins is the lack of magmatic activity..
70) Transform boundary seismic activity generally tapers off beyond the offset ridges or trenches.
71) No lithosphere is created or destroyed along transform plate margins.
72) Transform margins commonly comprise several parallel fault traces.
73) Different offset features which terminate at a transform boundary may show different amounts of offset.
74) The north and south ends of the San Andreas fault act pretty much independently.
75) Aseismic creep results in an accumulation of elastic stress.
76) Continental transform boundaries form topographic highs because they are resistant to erosion.
77) Transform faults on land form natural pathways for the transmission of groundwater.
78) Both thrust faults and extensional basins may be caused by strike-slip faulting.
79) Slippage along transform faults on spreading ridges is frequently oblique.
80) A bend to the left on a right-lateral fault would cause transtension.
81) Transform faults and fracture zones are the same thing.
82) Transpression along a strike-slip fault may generate thrust faults and folds.
83) Flower structure results from oblique transform fault offset.
84) Regional transpression may result from oblique plate interaction.
85) Releasing bends along a strike-slip fault provide sediment for confining-bend basins.
86) A right-lateral strike-slip fault on land with a right angle jog to the right would form a pull-apart basin.
87) Compressional duplex faults form in a transtensional environment.
88) The potential for preservation of sediments in an extensional duplex is smaller than in a compressional duplex setting.
89) Large scale fault zones usually manifest as a set of short, en echelon fractures.
90) In the Salton Trough, sedimentation lags behind subsidence.
91) Fracture zones trace relative plate motions on either side of a spreading ridge.
92) Fracture zones tend to be subtle bathymetric features which require high resolution sonar for study.
93) The opening of the Gulf of California and the origin of the San Andreas Fault coincide in time.