Lab # 5 - EARTH CYCLES

Introduction

This lab looks at the plate tectonic cycle and the carbon cycle. Two spare copies of the diagrams are provided at the end of this handout for your "neat copies".

Use your lecture handouts, lab 1 notes, and the lecture notes on the WWW to help you answer the questions. Additional information is provided here.
 
 

 Plate tectonics, crustal composition Plate tectonics is the hypothesis that the earthís surface is subdivided into rigid lithospheric plates that move relative to each other. Oceanic crust is created by upwelling mantle material, brought to the surface as basalt along mid-ocean ridges (or isolated hotspots, such as under Hawaii and Yellowstone). The mid-ocean ridges are examples of divergent (moving-apart) plate boundaries (e.g. Iceland, which sits on the Mid-Atlantic Ridge). Due to itís origin within the undifferentiated mantle, oceanic crust is composed largely of Fe-, Mg- and Ca-silicates, and as such has quite a high density (3 g/cm2). Continental crust has a lower density (2.7 g/cm2), and is made up mostly of aluminosilicates. When 2 oceanic plates collide they form a volcanic island arc (e.g. Japan); one of the plates is subducted under the other. When an oceanic and continental plate collide, the oceanic plate is subducted beneath the continent (because of the density differences), and a volcanic arc is formed on the edge of the continent (e.g. the Andes). When 2 continents collide (e.g. the Himalayas) an orogenic mountain belt is formed, and the lithosphere is dramatically thickened underneath this region (the continents both have low densities and hence neither is subducted). No volcanism occurs here because molten magma solidifies before it reaches the surface. These collision zones are called convergent plate margins.
 
  Chemical components of common sedimentary rocks Rock type Main components

Limestone CaCO3, MgCO3

Sandstone SiO2

Coal C,H,O

Black shale SiO2, C

Chert SiO2

The elements most important to earth cycles are C, O, Si and Ca.

 I. PLATE TECTONIC CYCLE
 
  A. On the diagram: 1. Label the following features: Continental crust, oceanic crust, subduction zone, mid-oceanic ridge, sediments, volcanic arc. (Each may occur in more than one place.)

2. Indicate where the following occur: Metamorphism, volcanism, crustal melting. (Each may occur in more than one place.)

3. (a) Where is heat generated?

(b) Where does this heat manifest itself at the surface?

 B. Rock samples - for each one: 4. Indicate where (in words or on the diagram) it is to be found.

5. What processes of the Plate Tectonic cycle is it formed by?

 C. Other questions: 6. How thick is the oceanic crust? the continental crust (range)? average crustal thickness? the oceanic lithosphere? the continental lithosphere?

7. What layers (& parts of layers) of the earth make up the lithosphere? What elements make up the lithosphere?
 
 
 
 







II. CARBON CYCLE
 
 

We are now going to consider the carbon cycle, using the plate-tectonic framework.

A. On the diagram:

1. Indicate the directions of transport of carbon (use arrows).

2. For each arrow,

(a) Name and describe the process in words.

(b) What chemical reactions occur?

3. Where are the carbon sources?

4. Where are the carbon sinks?

 B. Rock samples - for each one: 5. Indicate where (on the diagram) it is to be found.

6. What (if any) element does it act as a sink for?

7. State its role (if any) in the carbon cycle.
 
 
 
 
 
 
 







1. Plate tectonic cycle
 
 












2. Carbon cycle