Calavera Hills Virtual Fieldtrip

Please read instructions and preview the virtual lab before beginning.  Clip and complete this web-lab text in Microsoft Word (or other word processor) and submit inside your for online course, or print and hand it in for in-person classes.  Do not highlight or underline answers as they will not be preserved in the online format.

Part 1

1 Relative dating concepts (look in your book, or here relative dating)

Briefly define the following with respect to relative age-dating techniques. You will NOT be able to complete the lab without understanding these concepts!!

a.    Superposition

b.    Law of inclusions

c. Cross-cutting relationships

2 Igneous rocks

a.    How do you tell an intrusive (plutonic) igneous rock from an extrusive (volcanic) igneous rock in terms of grain size?

b.    In terms of color, how do you tell a felsic, intermediate or mafic extrusive igneous rock apart?

3 Igneous Rock Classifications Review

a.    Felsic intrusive: Granite/Tonalite

b.    Felsic extrusive: Rhyolite

c.    Intermediate intrusive: Diorite

d.    Intermediate extrusive: Andesite

e.    Mafic intrusive: Gabbro

f.     Mafic extrusive: Basalt

Part 2

On this fieldtrip we have seen 3 different rock units.  Given the details seen at each stop how would you answer the following questions.

1. Stop #1 Green Valley Tonalite

How would you describe the composition and texture of this rock?

2a Stop #2 Volcanic Dome

How would you describe the composition (color) and texture of this rock?

2b Stop #2 Relative Dating- Crosscutting Relationships

b. Using the Principle of Crosscutting Relationships, what are the relative ages of the Santiago Formation and Volcanic Dome? Why?

3. Stop #3 Relative Dating- Principle of Superposition

Using the Principle of Superposition, what are the relative ages of the Green Valley Tonalite and Volcanic Dome? Why?

4. Stop #4 Relative Dating- Principle of Inclusions

Using the Principle of Inclusions, which rock unit (Green Valley Tonalite or Volcanic Dome) using relative timing? Why?

5. What are the relative ages of the rocks (oldest vs. youngest rock units) for the Santiago Fm, Green Valley Tonalite, and Volcanic Dome at Calavera Hills?

6. How do we come up with the age of Miocene (about 20 MYO) for the volcanic plug? If you refer to relative dating please be specific. Make sure you read all of the background information. Hint: what technique gets you closest in age to Miocene?

7. Is there any part of this Web-lab you would improve?  Did you find any specific parts hard to follow or understand?

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