1. Working Out The Accreted Terrane Jigsaw Puzzle
2. Virtual Field Sites

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I. Working Out The Accreted Terrane Jigsaw Puzzle

Each of the following lists corresponds to a column in the table below. You will use the appropriate numbers and letters in the table to characterize the selected terranes listed in the left column of the table.

Column heading Crust Type(s)
Accreted terranes in the Pacific Northwest tend to consist predominantly of one of the following types of crust:

1. oceanic crust formed far from a continent
2. ophiolite
3. island arc
4. sediments deposited in an oceanic setting near a continent

Column heading Location
Accreted terranes of the Pacific Northwest are located in the following areas:

1. Blue-Wallowa-Seven Devils Mountains
2. In or near the Kootenai Mountains in southeastern British Columbia and north-northwest of Spokane, Washington
3. In the intermontane plateaus of central British Columbia and the Okanogan Highlands in Washington
4. The Methow-Tyaughton valleys
5. The eastern and central North Cascades of Washington and the British Columbia Coast Plutonic Complex, which is in the coastal mountains of mainland British Columbia
6. The western North Cascades and the San Juan Islands of Washington
7. Vancouver Island to southeastern Alaska
8. The southern tip of Vancouver Island through coastal Oregon, including the Olympic Mountains of Washington

Column heading Accretion Period
Accreted terranes of the Pacific Northwest have been added to North America primarily in the following time intervals:

1. The Jurassic Period
2. The middle to late Cretaceous Period
3. The Tertiary Period

Column heading Terrane Group
Accreted terranes of the Pacific Northwest can be separated into the following groups:

125. Terranes accreted during the Jurassic Period besides those in the Intermontane Superterrane
126. Terranes of the Intermontane Superterrane
127. Terranes accreted during the Cretaceous Period besides those in the Insular Superterrane
128. Terranes of the Insular Superterrane
129. Terranes accreted during the Tertiary Period

For each of the following terranes, use the appropriate numbers and letters from the lists above to indicate which type of crust it consists of, where is can be found in the Pacific Northwest, when it accreted, and which group it belongs to. Use the Web as a research tool and share information with other students while doing this part of the lab.

II. Virtual Field Sites

Tour the Rosario Beach Virtual Field Site and answer the following questions.

1. Name and explain* two types of evidence that the rocks at Rosario formed on the ocean floor. (*Explain means make clear how that type of rock points to an oceanic origin).
2. What type of rock that originates in the mantle is not found at Rosario (but does crop out a few miles away)?
3. hat other rock types usually found in an ophiolite are not seen at Rosario, as far as the Virtual Field Site shows?

Tour the San Juan Island Virtual Field Site and answer the following questions.

4. Describe specifically the type of evidence that indicates the Deadman Bay Volcanics originated in the Tethys Sea area. Also, describe where the Tethys Sea was.
5. How are the geologic structures in the shear zone and Lopez Structural Complex relevant to the theory that San Juan Island consists of accreted terranes?
6. What type of rock did the lime produced in the kilns at Lime Kiln Point come from?

Tour the La Push Virtual Field Site and answer the following questions.

7. Name four types of rock in the Hoh Terrane. (Note: Melange is not a rock name.)
8. In which period or periods of geologic time was the Hoh Terrane accreted?
9. What has caused the shoreline in the LaPush area to uplift approximately 50 feet in the last 8000 years?
10. At that rate, how much uplift would occur in one million years?

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