1. Orogenies and Rocks
2. Orogenies and Plate Tectonics
3. Virtual Field Sites

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I. Orogenies and Rocks

Refer to your collection of Pacific Northwest Geology rocks for the following questions.

Note that if you don't have the course rock kit, just use the photographs and properties of the rocks you have been shown in the PNW Geology online classroom, and your results from Lab 3A.

1. Orogenies are subjected to volcanism, especially in the form of chains of composite cone volcanoes. Name the specific type of rock in your rock kit that comes from this type of volcanism.
   
2. In terms of the rock cycle, how did the type of rock you named in the previous question form? (Was it consolidated from a layer of volcanic ash that fell from the sky? Did it accumulate as a layer of sediment in a tropical ocean? Or...how?)
   
3. Orogenies are subjected to intrusions up to the size of batholiths. Name the specific type of rock in your rock kit that comes from this type of igneous intrusion.
   
4. Describe how the type of rock you named in the previous question formed.
   
5. Orogenies are subjected to regional metamorphism. One result of high-temperature regional metamorphism is the formation of metamorphosed intrusive rock. Such rock may look like a granite or granodiorite in which the minerals were stretched out into layers or lineations. Name the specific type of rock in your rock kit that comes from this type of metamorphism.
   
6. In a subduction zone, at the leading edge of a zone of orogeny, oceanic crust may become rapidly buried, metamorphosed, and then rapidly uplifted into the continental crust. In the subduction zone pressure rises rapidly while temperature increases slowly, resulting in "high-pressure, low-temperature metamorphism." If basaltic oceanic crust metamorphoses in such conditions, it may grow blue and green amphiboles among its metamorphic minerals. Name the specific type of rock in your rock kit that comes from this type of metamorphism.
   
7. As a large mountain range undergoes uplift and erosion, it may eventually shed feldspar, mica, quartz, and other minerals common in the granitic and gneissic rock that are the core of the mountains. These rocks that form deep in the crust beneath the mountains become exposed at earth's surface after erosion has cut deeply into the range. The grains of feldspar, mica, quartz, and other minerals may accumulate into a common type of sedimentary rock. Name the specific type of rock in your rock kit that forms from lithification of such sediment.

II. Orogenies and Plate Tectonics

To research your answers to this section, you will need to do some research on the Web. Go to a search Web site such as http://www.google.com and in the window type such terms as "orogeny Sevier fold thrust" or "orogeny Rocky Mountains block Eocene" and have the search engine conduct a search. It will find and list for you a selection of Web pages, mainly Web sites for geology classes. Pick and choose carefully among the Web pages. Anybody can put anything on the Web, so try to pick credible Web sites to refer to (such as those put up by geology professors at major universities, or US Geological Survey, NASA, or other US Government Web sites). Glean some information from your search to give you ideas for answering the following questions.

To receive credit for answers taken from other sources, you must cite your source(s). For Web sites used to answer this assignment, you can just copy the URL of the main Web site (or Web sites) and include it in your answer.

8. The Sevier Orogeny occurred during the Cretaceous Period (possibly starting in the Jurassic, and in some places continuing into the Tertiary Period). It involved folding and thrust faulting of large regions of the upper crust, including parts of Idaho, Wyoming, Montana, and western Alberta. Describe specifically how the Sevier Orogeny may be linked to tectonic plate interactions along the edge of the continent. Include a description of what was happening along the western edge of the North American plate at that time, which plates were involved, and how those plates were interacting.
9. The Laramide Orogeny occurred during the Cretaceous Period, and continued into the mid-Tertiary Period in some locations. It involved reverse faulting and uplift of deeply rooted blocks of the continental crust. The Laramide Orogeny created mountain ranges in many of the Rocky Mountain states, especially Wyoming and Montana. Describe specifically how the Laramide Orogeny may be linked to tectonic plate interactions along the edge of, and beneath, the continent. Include evidence of what was happening along the edge of the North American plate at that time, which plates were involved, and how those plates were interacting. Also, be sure that this answer includes a description of how this would have affected deeper parts of the continental crust than did the Sevier Orogeny.

III. Virtual Field Sites

Explore the North Cascades Virtual Field Site and answer the following questions.

10. What two orogenies do the North Cascades illustrate?

For each of the following geologic processes that occur during an orogeny, name a specific rock formation with a capitalized name (for example, the Skagit Gneiss) or else name a specific geologic structure (for example, the Jack Mountain Thrust).

For each answer, name a specific rock formation or geologic structure, in the North Cascades, which is seen or explained in the North Cascades Core Virtual Field Site.

For example, "thrust fault" is not a specfic fault found in the North Cascades. "Jack Mountain thrust," on the other hand, is, indeed, a specific thrust fault found in the North Cascades.

11. faulting (reverse, thrust, or strike-slip)
12. folding (of sedimentary strata)
13. volcanism
14. igneous intrusions, including batholiths
15. metamorphism
16. deposition of sediments in basins between or beyond the mountain ranges

Re-explore the Sun River Virtual Field Site and answer the following questions.

17. What orogeny are the geologic structures of Sun River part of?
18. Why is it a stretch to link the Sun River structures to processes at plate boundaries?

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