Lesson 6: Continental Rifting
Starting this week the format of our course will change a bit. From now on we'll be looking at a different tectonic setting each week, and exploring how the processes that operate there shape park landscapes. This week, for example, we'll consider rift zones that form at divergent boundaries. Our focus will be on continental rifts because, for obvious reasons, mid-ocean ridges make better marine sanctuaries than national parks!
As you read through chapter 3 on continental rifts it will be helpful to take notes so that you can keep track of major ideas and have ready access to what you've learned when we refer back to these concepts later in the semester. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page. Also, note that our exercise this week is to write an outline of the first article you have chosen.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Outline how the elevations of continental rift systems change as rifting progresses, why this change occurs, and how you could use the elevations of rift valley floors to assess the relative age (early, middle, late) of a rift system.
- Explain why volcanism is associated with continental rifts, how the compositions of lavas change as rifting progresses, and why this change occurs.
- Describe the key features that characterize basin and range topography, including the type of faults that separate crustal blocks in such areas and the basic differences in rock types that underlie basins versus ranges.
- Compare and contrast the Basin and Range/Rio Grande and Keweenawan rift systems in terms of location, age, and current activity.
- Recognize common small-scale features that are associated with basaltic volcanism–such as spatter cones, columnar jointed lava flows, and lava tubes–and describe how each is formed.
- Briefly describe what an ophiolite is, which rock types it contains, and how ophiolites differ from "in-place" oceanic lithosphere.
Reading and Browsing Assignment
- Read Chapter 3, focusing on the topics outlined in the learning objectives above.
- To learn more about ancient rifting in North America, check out the geologic history and process that shaped Voyageurs National Park in Minnesota.
- To learn more about more recent (Cenozoic) rifting in western North America, check out the U.S. Geological Survey and National Park Service's geologic overviews of Death Valley National Park, Great Basin National Park, and Mojave National Preserve.
Exercise 6 (Due by 9:00 AM on Monday, 22-Feb-2010)
This week's exercise is to complete the first of our four writing assignments. To learn about the assignment click on the "Resources" link on the left side of this page, scroll down, and click on "Writing Assignment" near the bottom of the page. This week we'll be completing steps one and two and you'll be turning in the outline of the article you choose from the first set.
Your first task is to choose one of the two articles in Set 1 and to read that article carefully. You'll find that a pdf of one article is linked directly to the page, so just download and read it. Next, write down notes on your key observations and conclusions. Don't hestitate to post a note to the discussion board or contact me by private message if you have questions about an unfamiliar term or idea. Finally, write an outline of the article's major conclusions and supporting evidence by following the format of the "sample outline" that's linked to the Writing Assignment page.
In order to organize your outline imagine that you are telling a friend who hasn't read the article what its three or four key conclusions are and what data or observations were presented to support each of them. You want to do your best to focus on the main points of the article and not on minor details.When you write your outline you do not need to copy the sample outline exactly (e.g., same font and bullets), but be sure to include the complete article citation, your "PIN" (last 5 digits of your Etudes user id), and the course name and date at the top. Write your outline in complete sentences (not single words or phrases) and be sure that it is well organized and coherent so that a reader can follow the main themes of the article.
Before you start writing you should check out the outline grading rubric that is linked to the Writing Assignment page so that you can see what criteria I will use to evaluate your outline. There is no set length for your outline, but if it's longer than about a page or page and a half it won't be as helpful when you go to write your abstract. (Abstracts are very short, so the more you can winnow the article's main themes from its peripheral details when you prepare your outline, the less work you'll have to do later). Also, if you print a copy of the article be sure to save that copy so that you'll have it to refer to in a couple of weeks when you'll be writing the corresponding abstract.
When you have completed your outline go to the Etudes site for our class, go to Exercise 6 in the Etudes "Assignments, Tasks, and Tests" tool and submit your outline as an attached file. Outlines are due by 9:00 AM next Monday (22-Feb-2010.) I'm asking you to send it as an attachment rather than pasting it into a text box because this will preserve your formatting. You should send it as an MS Word document or, if you write it in another program, as a Word-compatible file. If you have any problems just let me know. I will return your outline to you by 1-Mar-2010, and the second part of this assignment, an abstract of the same article, will be due on 8-Mar-2010.
Quiz 6 (Due by 9:00 AM on Monday, 22-Feb-2010)
After you feel you have met the learning outcomes outlined above, please complete Quiz 6 in the Etudes "Assignments, Tasks, and Tests" tool. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around continental rift zones pretty well and are ready to move on to learn about parklands developed along passive margins next week.