MONTEREY PENINSULA COLLEGE
GEOLOGY 2
LAB 4: Structural Geology, Maps, & Cross-Sections
Sedimentary & Metamorphic Rocks
Goal: To be able to interpret a geologic map, determine the general attitude of a planar rock unit from its
outcrop pattern, describe the geometry of folds, and faults, and draw a simple cross-section.
Examine the rock specimens at the front desk.
chert
shale
siltstone
lithic sandstone
quartz sandstone
conglomerate
limestone
slate
phyllite
schist
gneiss
marble
quartzite
serpentinite
1.
What does “fissile” mean?
2.
3.
How are fissility and foliation different?
4.
Which rocks are crystalline?
5.
Which rocks are granular?
6.
Sketch interlocking crystals (crystalline)
7.
Sketch cemented grains (granular)
8.
What test do you use to distinguish between limestone and marble?
9.
Identify the unknown rocks numbered 1 through 8 (on the desks).
1.
5.
2.
6.
3.
7.
4.
8.
What does “foliated” mean?
Remember: Take Notes! You can use your mineral & rock ID notes & this lab, but not your book, on quizzes and
tests…
10. How do you distinguish between quartz and feldspar grains in sandstone?
11. Quartzite is a metamorphosed version of what rock (i.e. what is the protolith of quartzite)?
Review the concept of strike and dip (Figure 1).
strike
a horizontal line;
a compass bearing relative to north
(a water drop on an inclined surface will run in the down-dip direction)
(dip is the angle from horizontal down to the surface you’re measuring)
12. How does a strike-slip fault differ from a dip-slip fault?
13. What type of fault is the San Andreas Fault; strike-slip or dip-slip?
dip (perpendicular to strike)
MONTEREY PENINSULA COLLEGE
GEOLOGY 2
14. Label the strike (and direction), dip (and
angle), and fold axis symbols on the map to
the right (North is to the top of the page).
When looking at a map of a syncline, where
are the oldest rocks…in the hinge area of
the fold, or outwards towards the limbs?
Label the following features on the sketch of the fold to the right:
15. hinge
16. limb
17. axial plane
Review the “Rule of V’s” (Figure 2; attached).
Inclined planes “V” up-dip as they cross ridges.
Vertical planes are not deflected (do not “V”) by valleys or ridges.
The outcrop pattern of horizontal planes will parallel topographic contour lines, and will “V” upstream as they cross valleys.
Planes that dip downstream—and have a steeper dip than the stream—“V” downstream.
Planes that dip downstream—and dip the same as the stream—appear to parallel the stream.
Planes that dip downstream—and have a gentler dip than the stream—“V” upstream.
Planes that dip upstream, “V” upstream.
Review fault geometry (Figure 3, below).
footwall
fault plane
hangingwall
(in this figure, the hangingwall block has moved in the
down-dip direction relative to the footwall block)
18. Fractures in bedrock across which movement has taken place are called…
(a) joints, (b) faults, (c) cracks, or (d) crevasses?
19. On a normal fault, the hangingwall block has moved_____relative to the footwall block…
(a) up, (b) down, or (c) horizontally?
20. Is a subduction zone similar to a very large (1) normal fault or (2) thrust fault?
Use the Figure on page 71 of the lab book to answer questions 21-23.
21. What is the name of the type of contact that exists between the Vishnu Schist & the Tapeats Formation?
22. What is the name of the type of contact that exists between the Grand Canyon Series & the Tapeats Formation?
23. What is the name of the type of contact that exists between the Bright Angel Shale & the Tapeats Formation?
MONTEREY PENINSULA COLLEGE
GEOLOGY 2
Review the handout of topographic map symbols. You will need to use them to interpret the map on Page 179.
Review outcrop patterns on pages 164-173 in the lab book. They will help you to interpret the map on Page 179.
Refer to the map on Page 179 to answer questions 24 through 26.
24. How do the outcrop patterns show you that most of the Paleozoic strata (i.e. layered rock units) in the area are
horizontal?
25. What is the word (meaning “tree-like”) describes the drainage pattern you see in the Grand Canyon?
26. What rock units form cliffs?
Which form slopes?
Answer the following questions from the video program titled Sedimentary Rocks: The Key to Past Environments:
27. Who conducted the first geologic study of the Grand Canyon?
28. What does “clastic” mean?
29. Name 2 places where chemical sedimentary rocks form.
30. Name 3 types of sedimentary structures.
Answer the following questions from the video program titled Metamorphic Rocks:
31. Will an unmetamorphosed sandstone and its metamorphosed version have the same radiometric age?
32. What does “protolith” mean?
33. How does a “snowball” garnet form?
There are 2 main types of metamorphism.
34. a. _________________ metamorphism (mostly driven by temperature) is when cold rocks are intruded by hot rocks.
b. _________________ metamorphism (driven by both temperature and pressure) occurs at convergent plate margins.
35. Blueschist rocks form at very unique temperature and pressure conditions. What are these temperatures and
pressures?
Answer the following questions from the video program titled The Earth’s Structures:
36. If you were planning to build your own home, what valuable information could you gain from reading a geologic map?
37. Name the four basic types of folds, in order of increasing stress.
38. What do petroleum geologists learn from reflection seismographs?
Define (or sketch) the following:
structural geology:
strike:
dip:
attitude:
plunge:
trend:
anticline
fold axis
syncline
lineated
hinge
foliated
plunging fold
normal fault
recumbent fold
thrust fault
axial surface
reverse fault
overturned fold
strike-slip fault