These questions should give you an idea of the kind of thinking I am after, and the way the questions may be structured. Answers to the questions, along with the reasoning, are given at the bottom of this page. I suggest that you try to take this exam without looking at the answers -- then check and see how you've done. When you miss a question, use my explanations to help figure out where you went wrong.
1. Which one of the following minerals does not contain silica tetrahedra?
a. quartz b. feldspar c. olivine d. clay e. calcite
2. Diamond and graphite are both minerals made of pure carbon, yet diamond is clear, very hard, and relatively dense (heavy), while graphite is silvery-black, very soft (pencil lead is graphite), and relatively light. How can you best explain this difference? (Mark statements true or false, then choose answer.) ____diamond is made of one isotope of carbon, while graphite consists of a different carbon isotope ____diamond and graphite have different crystal structures ____diamond forms under very high pressure and temperature, while graphite forms at much lower pressures and temperature ____graphite forms at very high pressure and temperature, while diamond forms at low pressure and temperature ____graphite is simply diamond that has been weathered at the earth's surface.
The correct matching sequence is: a. TFFFF b. FTTFF c. FTFTF d. FFFFT e. FFFFF
3. If a basalt were heated up until it melted thoroughly (no crystals left) and then was cooled very very slowly you would most likely get:
a. gabbro b. andesite porphyry c. granite d. diorite e. obsidian
4. Many granites are thought to originate by
a. partial melting of the upper mantle b. settling out of quartz and feldspar from peridotite c. deep burial, melting, and recycling of continental&endash;type material (especially sedimentary rocks) where two lithospheric plates are colliding d. melting of the tops of downgoing lithospheric slabs (in trenches) together with contamination by continental material as the melt rises through the crust e. metamorphism of andesitic rocks
5. Which mineral below is extremely unlikely to occur in a basaltic rock?
a. plagioclase b. amphibole c. pyroxene d. olivine e. quartz
6. A very angular, poorly sorted sand made of quartz and feldspar probably
a. has been recycled through the sedimentary rock-forming process several times b. was deposited in a nearshore shallow sea environment c. represents strong weathering in the source area and long transport d. may have been transported by wind (as sand dunes) e. none of the above (a-d) are likely to be true.
7. In which environment below would the sediments probably be most poorly sorted?
a. deep lake b. sand dune c. beach d. landslide e. river channel
8, A very dense, very fine-grained metamorphic rock suggests metamorphism primarily as a result of
a. high pressure and high temperature b. high pressure and lower temperature c. low pressure and low temperature d. lower pressure and high temperature e. migration of chemical fluids
9. The best evidence that a rock has a metamorphic origin is:
a. finding mica in the rock b. presence of different-colored layers in the rock c. a foliated texture d. finding garnets in the rock e. finding phenocrysts in the rock
10. Where would you most expect to find large strike-slip faults?
a. mostly in the central areas of continents b. in places where lithospheric plates are sliding by one other c. in areas of crustal extension or stretching such as on mid-oceanic ridges or in uparched continental areas d. in areas of crustal shortening such as fold-mountain belts and subduction zones e. mostly in volcanic arcs
11. If you visited a large island located in a volcanic arc (such as Japan) which of the
following geologic conditions would you expect to find? (Mark true or false, then choose answer)
___very deep earthquakes
___thrust faulting and active andesitic volcanoes
___very thin crust
___normal faulting and active basaltic volcanoes
___mostly very old rocks
The correct matching order is: a. TTTFT b. TTFFF c. FFTTF d. FFFTF e. TFFTT
12. In places where two oceanic-type lithospheric plates are separating we would generally expect
to find (mark statements T or F, then choose answer)
___shield volcanoes
___a volcanic arc
___normal faults
___andesites
___very deep earthquakes
The correct matching order is a. TTTTT b. FTFTF c. TTFTT d. FTTTF e. TFTFF
13. Under the sea-floor spreading theory, the ocean floor:
a. contains the oldest rocks yet found on earth b. is very young at the mid-oceanic ridges and gets older toward the trenches c. is oldest at the mid-oceanic ridges and gets younger near the trenches d. is everywhere the same age e. is everywhere less than 50 million years old
14. An itinerant earthquake prophet warns you that a giant earthquake is going to occur and "the entire West
Coast - back to Salt Lake City - will disappear under the sea like Atlantis." Are you worried? (Is this
possible?)
a. Yes, seismic studies have shown that large areas on continental crust occur on the deep-sea floor b. Yes, because there is an active subduction zone offshore pulling the continent down c. No, because continental material is less dense than oceanic material and both are "floating" on denser viscous mantle d. No, because a vast amount of mantle material would have to move quickly out of the way and the mantle is too viscous to respond that rapidly e. answers (c) and (d) are both correct
15. The diagram below shows the location of three seismograph stations (I, II, III) which recorded the
seismograms at right during a medium-sized earthquake. The different wave arrivals are shown by arrows.
To help you compare them, I have put an arbitrary time scale below the seismograms.
Four faults (A,B,C,D) are shown on the map. Based on the information contained in the seismograms,
along which fault did the earthquake occur? (For any particular fault, consider the epicenter to be
where I've put the asterisk.)
a. occurred on fault A b. occurred on fault B c. occurred on fault C d. occurred on fault D e. there is no way to decide from the information given; we need to know the magnitude in order to determine location
16. The two seismograms below were recorded at different stations during an earthquake. The stations happened to be
close enough to the epicenter to undergo noticeable shaking. Which of the following statements are true?
(mark True or False as you go, then choose answer.) The arrows indicate the wave arrivals.
____A was further from the epicenter than B ____the earthquake magnitude was greater at B than at A ____the earthquake intensity was greater at B than at A ____station A is probably located on bedrock, B is on natural or artificial fill
The proper matching order is a. TTFF b. FFTT c. FTFT d. TFTF e. FTTF
Answers (with reasoning):
1. e (all the others are silicates -- you just have to remember this)
2. b (diamond and graphite must have different crystal structures, since they have
the same composition, but different physical properties. Since diamond is dense,
it suggests that it was formed under high pressure.)
3. a (this requires that you understand igneous rock composition, classification, and the
effects of cooling rate on rock texture. Basalt and gabbro have the same mineral
composition; gabbro is coarse grained, thus it is the result of very slow cooling.)
4. c (granites are high silica -- and so are the average materials of continents;
all the other environments and processes would produce low or intermediate silica rocks)
5. e (quartz is a high-silica mineral, incompatible with the low-silica composition of a basalt)
6. e (very angular = didn't get transported very far or rolled against other grains very much;
thus can't have been transported a long distance, and can't have been deposited in
shallow nearshore environment where waves would keep rolling it against other grains.
Same is true for sand dunes.
poorly sorted = deposited quickly, or by an agent incapable of separating grain sizes;
thus unlikely to have been transported very far, can't have been deposited nearshore or
in dunes where waves or wind would winnow out the fines; also, repeated cycling through
sed rock forming process would tend to round & sort grains a lot.)
7 d (landslide just dumps stuff in a heap -- incapable of effective sorting)
8. b (fine grained suggests lower temperature -- higher temperature makes ions more mobile,
favors larger grains; very dense suggests high pressure -- minerals squeezed, get more
compact crystal structures on recrystallization)
9. c (foliated texture -- formed by parallel orientation of platy minerals due to recrystallization
under pressure -- is characteristic of many metamorphic rocks, Mica can be found in igneous and
sed rx, not just metamorphics. Garnets can be found in sed rocks -- incorporated from breakdown
of meta rocks. Phenocrysts are found in porphyritic igneous rocks. Sed rock can show differen
colored layers too.)
10. b (strike-slip motion occurs along transform boundaries -- places where plates are sliding past
one another, edge-to-edge)
11. b (deep earthquakes occur on the lower parts of downgoing slabs; an andesitic volcanic arc is
created above the downgoing slab as it melts. Thrust faults occur as the downgoing slab is
compressed against the other plate. Crust is moderately to very thick -- one plate is beneath
another. Crust is relatively young -- all that active volcanism.)
12. e (plates being pulled apart are in tension -- thus would expect normal faults; new basaltic
magma rises up from partial melting of upper mantle -- can form shield volcanoes. Oceanic
crust is thin to begin with -- new crust is probably even thinner.)
13. b (new ocean floor is formed at the ridges as the plates are pulled apart; old crust is destroyed
as it is subducted at the oceanic trenches.
14. e (to make the whole west coast sink below the ocean in an earthquake would require the rapid moving
out of the way of a vast amount of viscous mantle material -- which is physically impossible. Also
continental crust is of lower density, making it hard to submerge large areas of it in the mantle.)
15. a (the key to this is realizing that the space -- that is, the time interval -- between the P and S
arrivals indicates how far away the epicenter is. The P and S arrivals are closest together at
station I, and farthest apart at station III. So you are looking for the fault that is closest
to I and farthest from III, and an intermediate distance from II. Only fault A meets these criteria.)
16. b (the distance between the P and S arrivals is the same for both seismograms, so the two stations are
the same distance from the epicenter; since the stations are recording the same earthquake, the
magnitude is the same at both stations; the amplitude (height) of the seismograms indicates the amount
ground motion & shaking, so station B experiences the greater intensity, probably because it's on
some sort of fill, while station A, which doesn't shake near as much, is on bedrock)