Lab 3 – The Klamath Mountains and the San Juan Islands Intro: The Klamath Mounta
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Question
Lab 3 – The Klamath Mountains and the San Juan Islands
Intro: The Klamath Mountains in Oregon and the San Juan Islands in Washington have a remarkably similar structure and geologic history. While the San Juan Islands are technically part of the Cascade province, and the Klamaths are in a province of their own, both follow a model where younger slabs were slid in below the older ones. This configuration yields a counter-intuitive situation where the older rocks are on top of the pile instead of the bottom. You should also take note of the fact that all of the rock slabs in both areas are bounded by thrust faults. One author has likened this to a deck of cards which has been shuffled.
Task: Examine closely the diagrams on page 82 (structure of the San Juan Islands) and page 117 (structure of the Klamath Mountains). Also, examine the two pictures below which show the Klamath terranes in cross section and on a map view. Use your textbook as well as these additional web resources to gather information.
* Go to Oregon's DOGAMI (Oregon Department of Geology and Mineral Industries) website: http://www.oregongeology.org/sub/default.htm
Scroll to the bottom right hand side and click on Learn more about Oregon's geology.
Then click on Geologic Sightseeing. An interactive map of Oregon will come up. Click on the Klamath Mts. region.
If having problems with the site above, see the end of the document for workaround instructions*
http://myweb.facstaff.wwu.edu/bernieh/reprints/brown-gsa-cord-07-san-juans.pdf
Questions:
Which of the two areas has the oldest rock?
Which of the two areas has the youngest rock?
Does the placement of the slabs suggest that they were placed by a tectonic process? Which one?
Because in both cases, the slabs dip toward the East, it is then safe to say that they are related to the same plate movements North and South? Which ancient plate is likely responsible for the placement of the slabs?
What are the ophiolite structures in each of the areas? What are their names? What kind of economic products do they yield?
What are the limestone formations in each of the two areas? Do we have limestone or coral reefs developing off the Pacific Northwest shoreline today? What does this suggest about the climate zones of original source of the rocks that make up both areas?
Application:
In your own words, compare and contrast the two. Briefly summarize the similarities and differences of both areas with regard to their structure, age and origin.
Explanation / Answer
Klamath mountain has the oldest Rock of proterozoic age
San juan Island has the oldest Rock of middle to upper Paleozoic age sedimentary rocks,
Klamath mountain has the youngest rock of
Paleo pacific lithospheric plate under North American plate hence slab produced.
In Klamath mountain there are different types of ophiolites are present as.,
1) Josephine ophiolite
2) Trinity ultramafic - mafic complexes
3) Rettlesnake creek terrain
Limestone in Klamath mountain is of Permian age which is identified by presence of tethyan fauna.
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