HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.

HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks.
On the syllabus, one of the goals stated for this course is for you to be able to interpret how a
rock or outcrop (rock exposure) that you observe around Boulder, CO may have formed.
This homework continues to work on that goal by taking you to two localities around Boulder,
Chasm Lake on Longs Peak and Coal Creek Canyon, between Boulder and Golden and asking
you to identify the rocks present, interpret how those rocks have formed.
The rocks presented from these two localities are dated to be between 1.7 billion and 1.8 billion
years old.
Tip! Compile all of your homeworks and notes in order to complete this homework. You will be
referring back to the rock cycle, characteristics of minerals (homework#2), igneous and
sedimentary rocks (homework #3) and the conditions that they form under, in addition to the
metamorphic rocks and the conditions they form under we just discussed.

Pre homework questions (1 pt):
Below are statements that reflect some of what you should be getting out of this assignment.

Having Trouble Meeting Your Deadline?

Get your assignment on HW #4: Revealing Boulder’s Ancient History through Metamorphic Rocks. completed on time. avoid delay and – ORDER NOW

1. Before you complete the assignment, rate how true each of the following statements is for
you using a scale of 1-5, where
.
These answers for the pre-question are graded only for being complete (1 pt all or nothing)
and not what your answers are.
Your rating
(1 through 5)
1. I can identify the common rock forming minerals based on their
physical appearance and provided diagnostic properties
2. I am comfortable identifying if a rock is igneous, sedimentary, or
metamorphic based on appearance and description.
3. I can identify igneous and metamorphic rocks based on mineralogy
and texture
4. Based on the rock type (e.g. sedimentary, igneous, or metamorphic,
and its appearance. I can infer the conditions under how that rock
formed.

Location 1: Coal Creek Canyon, Colorado

Coal Creek Canyon is south of Boulder, near the intersection of Highway 93 and Highway 72.
The rocks that we are going to be reviewing are off of Highway 72 towards the Front Range.
Some of these rocks can also be seen in Golden Gate State Park near Golden.

Rock Sample #1

This crystalline rock has Interlocking,
visible crystals of one type of mineral.
The individual crystals are large and
appear to have grown to become tightly
packed. There does not appear to be any
alignment of the recrystallized minerals,
though faint lines that resemble bidirectional cross bedding can be seen.
The mineral is clear or whitish in color,
hard, and does not react to acid.

5. What is the mineral seen in this sample?

6. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?

7. What is the name of this rock?

8. What was the original rock (e.g. the protolith) of this sample?

9. Based on the picture and the description of rock sample #1, what process did the protolith
experience in order to become the rock it is now?

Increase in heat
Increase in pressure
Increase in heat and pressure
Partial melting
Fractional crystallization

10. Down below are the possible steps through the rocks cycle that created rock sample #1 in
Coal Creek Canyon. Using your knowledge of the rock cycle, place the events in the best order.
(Note: online the order of the choices will change, 1 is the oldest).

The rock is uplifted and brought up to the surface, where it is exposed
Sediments are deposited on a beach where the waves move back and forth.
Eventually the sediment is buried and lithified
Magma body intrudes the rock and assimilates some of the rock into its magma
composition and bakes the rocks at its edges
Older rock is uplifted and exposed at the surface and weathered. The sediment has
traveled a long distance from its original source and has become well rounded and well
sorted.

Rock Sample #2

Near Highway 72, there is a shiny rock that
breaks into plates. Layering is easily seen and
there are three visible minerals that can be
made out.
A. A shiny mineral that is dark in color that
can easily be peeled off into sheets.
B. A second shiny mineral that can also be
peeled off into sheets but is light in color
C. A translucent mineral that is glassy and
fractures.

11. What is mineral A in this sample?

12. What is mineral B in this sample?

13. What is mineral C in this sample?

14. What is the rock type of this sample? Sedimentary, Igneous, or Metamorphic?

15. What is the name of this rock sample?

16. Based on the picture and the description of rock sample #2, what processes did the
protolith experience in order to become the rock it is now? Choose one

o
o
o
o
o

Increase in heat
Increase in pressure
Increase in heat and pressure
Partial melting
Fractional crystallization

Rock Sample #3

Further west on the road, heading deeper into the canyon,
there are rocks with alternating light and dark bands.
The lighter bands consist of mineral A that is clear or
whitish in color, hard, and does not react to acid.
The dark color bands are made of mineral B that is black or
dark green in color, rectangular in shape (long compared to
their width) and is a silicate that cleaves in a nonperpendicular way

17. What is mineral A in this sample?

18. What is mineral B in this sample?

19. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?

20. Based on the picture and the description of rock sample #3, what processes did the protolith
experience in order to become the rock it is now? Choose one
o
o
o
o
o

Increase in heat
Increase in pressure
Increase in heat and pressure
Partial melting
Fractional crystallization

21. What is the name of this rock?

22. Considering both Rock Sample #2 and Rock Sample #3 from Clear Creek Canyon, what
type of metamorphism occurred here 1.7 billion years ago (contact or regional)? And what
geologic processes could have created those metamorphic events? Answer in one to two
sentences.

Location 2: Chasm Lake

Location 2 is Chasm Lake in Rocky Mountain National Park, close to Longs Peak. It is possible
to hike up to this location

Rock Sample #4

This rock is exposed on east facing side of
Long Peak, known as the "Diamond". It has
interlocking, randomly oriented, visible
crystals of three mineral types
Mineral A: Black, shiny, and breaks into
sheets
Mineral B: Pink in color, opaque, with a
rectangular crystal shape
Mineral C: Translucent and very hard. Does
not have any cleavage planes.
23. What is Mineral A?

24. What is Mineral B?

25. What is Mineral C?

26. What is the rock type of this sample? Sedimentary, Igneous, and Metamorphic?

27. What is the name of this rock?

28. Based on the picture and description of rock sample #4, what processes did the protolith
experience in order to become the rock it is now? Choose one
o
o
o
o
o
o

Increase in pressure
Increase in heat and pressure
Slow crystallization deep in the continental crust
Rapid crystallization deep in the continental crust
Slow that rapid crystallization in the continental crust
Weathering, deposition, and then lithification

Rock Sample #5

Interlocking, aligned minerals, give a layered appearance
to the rock and a nice shine. Three different types of
minerals are easily visible.
Mineral A: Red in color and a well formed 12 sided crystal
shape. Has a glassy luster to it.
Mineral B: Black, shiny and breaks into sheets.
Mineral C: Silver, shiny, and breaks into sheets.

29. What is mineral A?

30. What is mineral B?

31. What is mineral C?

32. What is the rock type of this sample? Sedimentary, Igneous or Metamorphic?

33. What is the name of this rock?

34.Based on the picture and description of rock sample #5, what processes did the protolith
experience in order to become the rock it is now? Choose one
o
o
o
o
o
o

Increase in pressure
Increase in heat and pressure
Slow crystallization deep in the continental crust
Rapid crystallization deep in the continental crust
Slow that rapid crystallization in the continental crust
Weathering, deposition, and then lithification

35. In some areas around Chasm Lake, you can see where Rock Sample #4 intrudes or cuts
into Rock Sample #5. Using this information along with you knowledge of the rock cycle and
how rocks form, place the following possible events in order to explain what happened to the
rocks of Chasm Lake. (note: the order of the choices will vary online, 1 is the oldest)
A mountain building event occurred, placed the rocks of Ancient Colorado under
tremendous amounts of pressure and in some cases burying them deeper
The magma body does not erupt at the surface. Instead stays at depth and the magma
slowly crystallizes
A magma body intrudes the preexisting rock and through assimilation become more
felsic.
Another unknown geologic event occur that uplifts rocks sample #4 and rock sample
#5 to the surface.
Minerals in the older rocks were unstable at the new temperature and pressure
conditions. Neocrystallization occurs creating new minerals over long periods of time.
An unknown rock, older than 1.8 billion years was part of an ancient continental crust.

36. Reviewing your answers for the five rock samples seen at these two location, what is the
possible geologic event that occurred in Colorado 1.7 -1.8 billion years ago? Justify your
answer by explaining how that event could create the rocks seen here.

Pre homework questions (1 pt):
Below are statements that reflect some of what you should be getting out of this assignment.

Before you complete the assignment, rate how true each of the following statements is for
you using a scale of 1-5, where
.
These answers for the pre-question are graded only for being complete (1 pt all or nothing)
and not what your answers are.
Your rating
(1 through 5)
37. I can identify the common rock forming minerals based on their physical
appearance and provided diagnostic properties
38. I am comfortable identifying if a rock is igneous, sedimentary, or
metamorphic based on appearance and description.
39. I can identify igneous and metamorphic rocks based on mineralogy
and texture
40. Based on the rock type (e.g. sedimentary, igneous, or metamorphic,
and its appearance. I can infer the conditions under how that rock
formed.

41. In the space down below, write a sentence on what skills or knowledge you are feeling
more confident on now after completing this exercise OR what questions you may still have
after completing this exercise.

Order Solution Now

Similar Posts