Igneous Fieldtrip Web-Lab

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.

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Part 1: Review

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 igneous rock from an extrusive igneous rock?

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

c.    What is the different in composition between a dacite and an andesite?

d.    What is the different in composition between a tonalite and a diorite?

a.    How does a volcanic neck form?

3 Igneous Rock Classifications

For each of the following, name the igneous rock type

a.    Felsic intrusive: Granite (example)

b.    Felsic extrusive:

c.    Intermediate intrusive:

d.    Intermediate extrusive:

e.    Mafic intrusive: Gabbro (example)

f.     Mafic extrusive:

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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

a.    How would the rocks appear different if they were aphanitic or extrusive in origin?

b.    How would the primary MINEROLOGY be different if these rocks were more felsic?

c.    How would the primary MINEROLOGY be different if these rocks were more mafic?

2. Stop #2 Dacite Volcanic Plug

a.    How would the rocks appear different if they were phaneritic or intrusive in origin?

b.    How would the COLOR of these rocks be different if they were more felsic?

c.    How would the COLOR of these rocks be different if they were more mafic?

Cont Stop #2 Relative Dating

a. Using the Principle of Crosscutting Relationships, which rock unit (Santiago Formation or Volcanic Plug/Dacite) is youngest? Why?

3. Stop #3 Which rock unit is older at Stop #3 using just the Principle of Superposition. Look under relative dating in your text or follow the links on the website.

4. Stop #4 Which rock unit is older at Stop #4 using just the Law of Inclusions. Look under relative dating in your text or follow the links on the website.

5. What are the relative ages of the rocks (oldest vs. youngest rock units) using (Santiago Fm, Green Valley Tonalite, Volcanic Plug/Dacite) 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?