1. A Simple Plate Tectonics Model
2. Mapping Plate Tectonics
3. The Rock Cycle
4. Virtual Field Site Questions
5. Checklist For Your Lab 4 Diagrams

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For parts II and III, Mapping Plate Tectonics and The Rock Cycle, you will make drawings. You can draw them digitally or draw them on real paper by hand. 

Submit your diagrams in digital form to the Lab 4 PT (plate tectonic map) assignment and the Lab 4 Rk Cycl (advanced rock cycle) assignments in the online classroom.

I. Plate Tectonics Model

In this section of the lab you will use a triangular paper cutout to represent a tectonic plate and the way it interacts with the plates along its boundaries. You will draw a plate tectonic map based on the model that shows all three types of plate boundaries. You will also use the triangle and plate tectonic map as a simplified model of the Plate Tectonics of the Pacific Northwest.

Use a ruler or straight edge to draw a triangle on a blank piece of paper. Make the triangle approximately 6 inches long on each side. Label the triangle A, the paper surrounding the triangle B, and number the sides of the triangle, as in the diagram below. Carefully cut the triangle out, leaving it and the paper it is cut out of with clean, straight edges. Do not cut through the paper around the triangle to get to the triangle. Leave the paper around the triangle intact.

The triangle, A (see diagram below), represents a moving plate. It is surrounded by one or more other plates, labeled B. To run the plate tectonic model, start with the triangular plate, Plate A, in place inside its triangular hole. Reach beneath the right side of Plate B to grasp the bottom right corner of the paper triangle. Slowly pull the triangle straight to the right, beneath the edge of Plate B at boundary 2.

Use the correct plate tectonic terminology in answering the following 6 questions. Answer each of the 6 questions with a single word.

1. What are the two plates doing at boundary 1?
2. What kind of plate boundary is boundary 1?
3. What are the two plates doing at boundary 2?
4. What kind of plate boundary is boundary 2?
5. What are the two plates doing at boundary 3?
6. What kind of plate boundary is boundary 3?

II. Mapping Plate Tectonics

Refer to the triangular plate tectonic model that you cut out and ran in Part I of this lab assignment.

Refer to the plate tectonic boundary map symbols in the Table of Plate Tectonic Boundaries.

Draw a plate tectonic map of the triangular plate and its surrounding plate(s).

Follow these instructions:

Be sure to use a ruler or straightedge to draw the plate boundaries as straight lines.

Important: In your plate tectonic map, use the proper map symbol for each type of plate boundary. The map symbol for each type of plate boundary is not something that goes on the map near the plate boundary or separate from the plate boundary itself. Wherever it is used on the map, the symbol for each type of plate boundary becomes the complete plate boundary itself.

A divergent plate boundary is drawn as a pair of parallel lines. At the ends of the divergent plate boundary, the lines must be closed off. In other words, where a divergent plate boundary ends by intersecting (running into) another plate boundary, each of the two parallel lines must continue to, and end in contact with, the line of the other plate boundary. 

A convergent plate boundary is drawn as a line with triangles (also called "teeth") on it. The triangles go on the upper plate, the one that is being thrust on top of the other plate.

A transform plate boundary is a line along which the correct types of arrows are correctly positioned.

Just one pair of arrows is usually needed to denote a transform plate boundary. (Unless a transform plate boundary is extremely long and curvy and hard to follow, in which case a pair of arrows can be placed every so often along the transform plate boundary line.)

The pair of arrows must be aligned parallel to each other and exactly across from each other on either side of the line.

The arrows do not have full arrowheads, they each have half or one side of an arrowhead, complementing the half on the other arrow.

Each arrow must point in the direction that the plate it's on is moving relative to the plate on the other side of the transform.

Also on your map, at the location of the Cascade volcanic arc, draw a line of inverted v shapes (like /\ only not so steep) to represent the chain of composite cones.

The chain of volcanoes in a volcanic arc is produced by the subducting plate when it reaches over 50 miles deep in the mantle, below the upper plate. There the subducting plate releases fluid, mostly water, into the mantle above it, which causes magma to form, rise, and erupt. Most of the magma is intermediate magma, which makes andesite, which piles up into composite cones like Mount Rainier and Mount Shasta and the other tall volcanoes of the Cascades volcanic arc.

Therefore, a volcanic arc is parallel to the convergent plate boundary, it extends the full length of the convergent plate boundary, and it does not go beyond the ends of the convergent plate boundary.

When a person draws a volcanic arc that does not run the full length of the convergent plate boundary, or runs beyond it at the end, or is not parallel to the convergent plate boundary, you can tell they do not understand how the subduction works to form the volcanic arc.

The triangular plate in your paper cut-out plate tectonic model, and the plates that border it along each of the three sides of the triangle, can be thought of as a simplified representation of the Juan de Fuca Plate and its surroundings.

Label the following on your plate tectonic map:

* Juan de Fuca Plate
* North American Plate
* Pacific Plate (labeled left of and below the triangular plate)
* Juan de Fuca Ridge
* Cascadia Subduction Zone
* Mendocino Transform

Note that there is no need, and should not be written on your plate tectonic map, the plate labels A and B, nor the plate boundary labels 1, 2, and 3, from the tectonic plate model. Those are used to ask questions about the plate model in the Lab 4 Answer Form. Do not write those letters and numbers on your plate tectonic map.

III. The Rock Cycle

Draw a more detailed version of the rock cycle. Call it the advanced rock cycle.

In the advanced rock cycle, there is no box for igneous rock. There is no box for sediment. There is no box for sedimentary rock. There is no box for metamorphic rock.

Instead, there are boxes for plutonic rock and volcanic rock (see the igneous rocks table).

There is a box for clastic sediment. There is a box for chemical sediment. (See the sedimentary rocks table, particularly the part about what sediment is before it gets turned into rock. This includes reading the first two paragraphs below the table.)

There is a box for regional metamorphic rock. There is a box for contact metamorphic rock. (See the metamorphic rocks table).

Draw labeled arrows showing how geological materials are transformed from one box to another in the rock cycle.

For example, draw an arrow going from magma to plutonic igneous rock labeled "slow cooling and crystallization within the earth," or "cools and solidifies slowly, underground," or something like that, so long as the label is sufficiently complete, succinct, and accurate. Label all the arrows.

Think of the advanced rock cycle as having two categories of sediment and six categories of rock.

In addition to the two categories of sediment and the six categories of rock, the advanced rock cycle also must have magma. Just magma, one word, one box, like in the basic rock cycle.

Magma and the two types of sediment are not types of rock, but they are just as essential to the rock cycle as the rocks are.

All igneous rock originates from magma, molten rock inside the Earth.

The two types of sediment exist under our feet, in our gardens (there is no soil without clastic sediment in it), in our roads and concrete, in rivers and deserts, in lakes, bays, and oceans, and everywhere else on Earth's surface. Clastic sediment is obvious: sand, gravel, boulders, silt, dust.

Chemical sediment is crystals of salt, or layers of calcium carbonate minerals, or layers of gypsum, or any other sort of chemical sediment: sediment that was deposited out of solution in water (or air) through a process called precipitation. Chemical sediments are only obvious in some places, such as salt pans in the desert, where playa floors are covered by layers of encrusted salt. Another form of chemical sediment is coral reefs. Inside of many coral reefs are lagoons with their bottoms covered by seashells and other remains of dead marine organisms, which is also chemical sediment.

(An even more advanced rock cycle would separate these out into another category called biogeochemical sediment, because it was living organisms that precipitated the minerals out of solution to build their hard parts such as shells out of, but we are going to hold back from that level of advancement on the rock cycle and leave it lumped together as just chemical sediment of any type, whether abiological or biological in origin.)

You cannot get chemical sedimentary rock unless you start out with chemical sediment that was deposited on Earth's surface, just as you cannot get clastic sedimentary rock unless you start out with clastic sediment deposited on Earth's surface.

Add up those six types of rock, two types of sediment, and magma, and, in the simplest version of an advanced rock cycle, you get nine categories, nine boxes:

1. plutonic igneous rock
2. volcanic igneous rock
3. clastic sediment
4. chemical sediment
5. clastic sedimentary rock
6. chemical sedimentary rock
7. regional metamorphic rock
8. contact metamorphic rock
9. magma

To describe how a rock, type of sediment, or magma was transformed from its preceding category in the advanced rock cycle, choose one of the following processes:

• cools and crystallizes slowly underground
• erupts and solidifies rapidly on the surface
• weathers, erodes into solid bits and pieces, is deposited
• weathers, dissolves, precipitates
• is lithified by burial, compaction, and cementation
• recrystallizes due to heat and directed pressure from deep burial and tectonic forces
• recrystallizes due to heat from a nearby body of magma
• melts due to more heat, lower pressure, or added water

These transformative processes serve as the labels for the arrows that join the categories together in the advanced rock cycle.

Draw labeled arrows showing how geological materials are transformed from one box to another in the advanced rock cycle.

For example, draw an arrow going from magma to plutonic igneous rock labeled "slow cooling and crystallization within the earth," or "cools and solidifies slowly, underground," or something like that, so long as the label is sufficiently complete, succinct, and accurate. Label all the arrows.

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To think our way through the advanced rock cycle, here is a written version.

Magma solidifies into either volcanic rock or plutonic rock. 

Every possible type or category of rock in the world, when we see examples of them at the Earth's surface, is undergoing physical and chemical breakdown to turn into clastic and chemical sediment. 

The clastic sediment and the chemical sediment are deposited (usually after some erosion, transport, and deposition of the sediment) in layers on the Earth's surface. 

The chemical sediment gets buried, compacted, and cemented into solid chemical sedimentary rock, the clastic sediment gets buried, compacted, and cemented into solid clastic sedimentary rock. 

If a clastic sedimentary rock, or a chemical sedimentary rock, or a volcanic rock, or a plutonic rock, is subjected to the added pressure and heat of deeper burial, or added tectonic stress, or added heat, or a combination, and it recrystallize into new minerals that are stable in the new conditions, then the rock has been transformed into metamorphic rock. It has been metamorphosed. 

If the metamorphic rock got that way only because of heat from a nearby intrusion of magma, it is a contact metamorphic rock. (Which, by the way, is not subject to increased pressure or stress as it gets heated by the nearby magma.)  

If the metamorphic rock got that way because of increased pressure that results from getting buried and pushed deeper in the crust (the deeper in the Earth a rock goes, the more pressure there is on it due to the weight of all the rocks on top of it), and by tectonic stress (pressure pushing on it unequally, as opposed to the equal-all-around pressure on it from the weight of all the rock above it), and by the heat that comes from being deeper in the Earth (the deeper one goes in the Earth, the hotter it gets), then the rock has undergone regional metamorphism. Regional metamorphism affects large volumes of rock, whole regions of them, so most metamorphic rocks are regional metamorphic rock. 

Most peoples' eyes will glaze over before they finish the previous paragraph. Poor metamorphic rocks, they are so poorly understood. Suffice it to say, when it comes to turning a pre-existing rock into a regional metamorphic rock, it will usually be subjected to increased pressure, stress, and heat, and that is what causes it to grow a new set of minerals and become a regional metamorphic rock.  

With even more heat, a metamorphic rock may melt, producing magma.  

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Refer to the numbers of the rocks in your Pacific Northwest Rocks kit. Write the number of each sample (numbers 1 through 9) in its appropriate box in the advanced rock cycle. For example, the number for basalt would go in the volcanic igneous rock box in your rock cycle diagram.

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IV. Virtual Field Site Questions

Tour the Tatoosh Range Virtual Field Site and answer the following questions.

7. What is the age sequence of the following three rocks (from oldest to youngest]): Tatoosh Pluton granodiorite, Mt. Rainier andesite, Stevens Ridge Formation dacite? Write the sequence from oldest (first) to youngest (last).

State which category each of the following three rock types are and state how each was transformed from its preceding category.

Rock Type	Category	Preceding Category	Transformed by*
Stevens Ridge dacite	8.	9.	10.
Tatoosh Pluton granodiorite	11.	12.	13.
Mt. Rainier andesite	14.	15.	16.

Note: To describe how a rock was transformed from its preceding category, see the list above of the transformative processes in the advanced rock cycle.

Note that these transformative processes serve as the labels for the arrows that join the categories together in the advanced rock cycle.

Tour the Hurricane Ridge Virtual Field Site and answer the following questions.

17. What type of plate tectonic boundary has caused rocks from the ocean floor to become mountains on the edge of the continent?

Think of the rock cycle as having six rock categories: plutonic igneous, volcanic igneous, chemical sedimentary, clastic sedimentary, regional metamorphic, and contact metamorphic, along with the categories magma and sediment. State which category each of the following three rock types are and state how each was transformed from its preceding category.

Rock Type	Category	Preceding Category	Transformed by**
Hurricane Ridge pillow basalt	18.	19.	20.
Hurricane Ridge sandstone	21.	22.	23.
Hurricane Ridge pencil slate	24.	25.	26.

**Note: To describe how a rock was transformed from its preceding category, choose one of the following processes:

• cools and crystallizes slowly underground
• erupts and solidifies rapidly on the surface
• weathers, erodes into solid bits and pieces, is deposited
• weathers, dissolves, precipitates
• is lithified by burial, compaction, and cementation
• recrystallizes due to heat and pressure from deep burial and tectonic forces
• recrystallizes due to heat from a nearby body of magma

Checklist for Lab 4 Diagrams:

1. You are sending in a MAP of the triangular plate model, NOT the cut-out plate model itself.
2. The plate boundaries on your map are symbols. In other words, the symbols for plate boundaries on the map are not off to the side of the plate boundaries; the symbols ARE the plate boundaries.
3. You show the Cascade volcanic arc as extending only where subduction is occurring, parallel to the convergent plate boundary and not past the ends of the convergent plate boundary.
4. Your rock cycle is an advanced, detailed rock cycle with nine categories (including both types of sediment), NOT the simple rock cycle you can find on the Web with five categories. Your advanced rock cycle labels ALL processes, including:
   • how each of the two sub-categories of igneous rock form
   • how each of the two types of sediment form
     (both types of sediment turn into sedimentary rock the same way,
     so only one process is needed to get to the two types of sedimentary rock)
   • how the two types of metamorphic rock form.

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