Mountain Belts and the Continental Crust and Geologic Structures


Rocky Mountain Uplift, “Artificial Garnet Schist”, and Strike Slip Demo videos.
To better understand STRIKE and DIP, please view– Strike and Dip

Note: Answers to “short-answer” questions should be no longer than a few sentences.

Note 2: As per instructions (“How to Turn In Assignments”)– make sure that you copy this assignment into a MICROSOFT WORD DOCUMENT, and place your answers below each question…. save it on your computer, and then UPLOAD the assignment using the “SUBMIT ASSIGNMENT” button!

1) Prof Win Means from Albany tries deforming “artificial rocks” in the laboratory– at much lower temperatures, much lower pressures, and over shorter time spans than are associated with real rock deformation in nature. In certain labs, really hi temperatures and pressures can be achieved, but of course, extremely long time spans can never be duplicated.
Look at the images of both the artificial and real quartzites. Answer the following question (explaining your answer):

Is there substantial space between the grains, or should we say that the grains are “interlocking” (minimal space)?

2) Read the sections on folded rocks. Think about why it is that rocks sometimes break (fault) and sometimes bend (fold).
Two Questions,
First, suggest an interesting geologic place to go see folded rocks. Be specific.
Second, explain what sort of geologic environment would enhance folding versus faulting? (In other words, what does it take to get rocks to bend as opposed to break?)

3) Read about “isostasy”—basically, you will find that mountains (in a way) float on the underlying mantle like icebergs float in the ocean. Most mountain ranges have deep “crustal roots” analogous to the fact that we only see the tips of icebergs!

Some mountain ranges, notably the Sierra Nevada and (to some extent) the Rocky Mountains LACK substantial crustal roots.

Question…WHY IS THIS?

4) First, review the different kinds of faults in the chapter on Geologic Structures (in particular the dip-slip types that include normal, reverse, and thrust).

Second, look at the information and figures on the geologic evolution of the southern Appalachians.

Yes, complicated, but in a general sense, what sort of basic dip-slip fault types would you expect to be associated with

a) The various orogenies (No need to be specific with Taconic, Acadian, Alleghenian– just consider “orogenies” in general!)

b) With the Triassic rifting event.

5) Consider a fault like the San Andreas. It is mostly all about side-to-side motion (no up-down motion), and hence we call it a strike-slip fault.

Review in your textbook about releasing bends and restraining bends, AND also check this out (clip and paste into browser)…

NOW…. Consider the bend in the San Andreas Fault, just north of L.A. Below is a schematic view, looking down, i.e. “map-view”.
(This bend is what we call a “right-step” in a right-lateral fault. This is because no matter which direction you are walking, IF you were to walk along the fault, you’d have to take a bend to the right!…. or, ha ha, perhaps drive down the fault, because nobody walks in LA.)

Think about the sort of stress regime exists near the fault line– specifically in the hachured area (angled black lines), and answer the following question:

Is this a region of squeeze (compression) OR a region of pull-apart (extension)? EXPLAIN YOUR ANSWER

Stress regime image

What type of fault would you expect to generate the unusual occurrence of older rocks sitting atop younger rocks:

A) Strike-Slip, B) normal, C) thrust

7A) What sort of rocks would you expect to find in the center of an eroded anticline (or dome)?
Young rocks or Old rocks? Explain WHY you chose young or old.

7B) Look at a picture of a subduction zone. Lots in your textbook!
What sort of fault is this? (thrust/reverse, or strike-slip, or normal?)

8) At the very end of the video “Rocky Mountain Uplift” (see click link at top of assignment), there is an image that shows the location of the numerous individual Laramide Mountain Ranges (rising around 70-40million years ago, and shown as the tan/grey outlines) AND the purple lines that outline the igneous activity of the Colorado Mineral Belt.

First–Is the igneous activity more or less aligned with the mountains OR does it cut across the mountains?
Second– Do all mountain uplifts involve igneous activity? (i.e., Does mountain uplift require magma rising from beneath?)

9) Click on the link above– “Strike Slip Demo” (at top of assignment)

This is a computer model of geomorphic development during fluvial incision with modification by strike slip faulting.

In plain English, that means…It shows how a landscape should evolve, with streams/rivers cutting into the earth, and then with a fault being introduced.

View the animation and answer the following three Questions–
A) Approximately, at what time-stamp in the video does the fault initiate? (How many minutes/seconds into the video)

B) What sort of strike slip fault is shown (pick one of the following)— right-lateral OR left-lateral

C) The video shows a feature known as “stream capture”. What do you think is meant by that term?

10) Change in shape of a rock is referred to as
A) Strain, B) Stress —–choose A or B.

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