Geology

GEOLOGY
1. Describe rocks using the following terms: texture, crystal size and structure, grain size,
layering, phenocrysts, fossils.

2. Describe how a range of igneous, metamorphic and sedimentary rocks are formed.

3. Classify igneous rocks as volcanic or plutonic according to silica levels and grains size.

4. Represent the rock cycle diagrammatically.

5. Complete a structured overview to show the relationship between igneous, metamorphic and
sedimentary rocks.

6. Use rock keys to classify rocks.

7. Construct a key to assist with the classification of rocks.

8. Relate physical properties of rocks such as grain size and layer width to the environment in
which rocks were formed

9. Link the type of rock formed to the environment in which it was formed.

10.Give the relative ages of rocks in a given stratigraphic column.

11.Investigate how geological records such as rock sequences, rock dating, fossils and rock
location, provide evidence for past events such as sinking land, rising land, rising magma,
depositing of sediments and plates subducting/diving.

Friday, 6 November 2009

Term Definition GLOSSARY 1
geology study of the Earth’s structure and its rocks
rock solid, non-living material that forms the earth’s crust
minerals natural substances with a definite composition and structure
elements substances made of identical atoms
compounds substances made of non-identical atoms bonded together
crystals solid substances showing definite geometrical shapes
solidify changing from a molten to as solid state
crystallise formation of crystals from molten rock or solution
amorphous describes solids which do not have a crystalline structure
lustre the degree of shine on the surface of a solid
mass of an object compared to the mass of the same
relative density
volume of water
used to describe an object which will affect a nearby
magnetic
compass needle
crystalline made out of crystals
transparent light passes through clearly
translucent light passes through but not clearly
opaque light does not pass through

crust the solid outer layer of rock that forms the earth’s surface
mantle deep layer of molten rock underneath the crust
molten in a liquid state because of high temperatures
magma hot molten rock from underneath the crust
igneous rock rock formed when magma solidifies
plutonic igneous
rock formed when magma solidifies inside the crust
rock
volcanic igneous
rock formed when magma solidifies on or near the surface
rock
ash fine dust in the cloud produced by a volcanic eruption
lava the molten rock that flows out of a volcano
sediment rock fragments, sand and mud that settles on the sea floor
weathering gradual breaking down and wearing away of exposed rock
sedimentary rock rock formed when sediment hardens on the sea floor
strata layers of sedimentary rock
fossils remains or impressions of ancient organisms
metamorphic rock rock formed under high pressure and temperature
recrystallise to change the type of crystals in a solid
rock cycle transformation of rock into different forms


protoplanet early stage in the formation of a planet
radiometric dating dating rocks by the ratio of daughter to parent atoms
radioactive decay atoms which can break down releasing radioactivity
geological period interval of earth’s history with unique flora and fauna
evolve modification of a species or formation of a new species
species similar organisms capable of breeding with each other
mass extinction a large number of species become extinct at the same time
flora & fauna collection of plant and animal species present
fossil record distribution of fossils in different rock strata
global
average annual temperature over the entire globe
temperature
global warming gradual increase in the average global temperature
meteorite large rock from space which collides with the crust
tectonic plates huge plates that the crust is broken up into
plate boundary junction between neighboring plates
convection current current in liquid caused by heated matter rising
seismic activity earthquakes and tsunami
mountain building crumpling up of the crust when plates collide
rock strata layers of rock with different minerals and fossils

THE EARTH’S
STRUCTURE

LAYERS - labelling & describing

Demo: The Scotch egg model of the earth’s structure Imagine a Scotch egg......
1. (breadcrumbs)
2. (sausagemeat)
3. (egg white)
4. (egg yolk)

Research - The earth’s structure http://www.windows.ucar.edu/tour/link=/earth/Interior_Structure/
interior.html

Diameter = ________ km. The inner core is so ___ that it causes
material in the outer core and ___________to move around.
_____________

____________ thin silicate rock material

___________
mostly solid (semi-liquid/plastic) and
_________ consisting of
________ _________

liquid and consisting of
________ & _________

solid and consisting of ________ &
_________

HOW THICK ARE YOU??

Study the diagram carefully.
It shows the earth’s layers.
The depth in kilometres of the
boundaries between layers is
shown.
1. Put the thickness of the
layers in order from
thickest to thinnest.
2. A calculator may help.

Thickest layer
____________
____________
____________

Thinnest layer ____________


HOW THICK ARE YOU??

shown.

Thickest layer
____________
____________
____________


Mantle thickness = 2890 - 80 = 2820 km
ANSWERS Outer core thickness = 5150 - 2890 = 2260 km

HOW THICK ARE YOU??

shown.

Thickest layer
____________
____________
____________


Note
Mantle thickness = 2890 - 80 = 2820 km Some sources of information will
ANSWERS Outer core thickness = 5150 - 2890 = 2260 km give the outer core as being thicker

LAYERS - defining them

Research - Definitions http://mediatheek.thinkquest.nl/~ll125/en/struct.htm

Use the URL above to match the definition with the term with the
composition with the thickness and with the average temperature

Thickness Average
Term Definition Composition
(km) temp (oC)
A. The layer above 1. Iron and Nickel. Extremely hot but (a) 2200 (i) 4500
Inner the core but below the pressure is low enough to allow it
core the crust to exist as a liquid.

B. The earth’s hard 2. Compounds of silicon, iron and (b) 15 (ii) 20
outer shell (which magnesium
Outer floats on the softer to
core part of the mantle)
870

C. The liquid layer 3. Rocks: Basalt and Granite (c) 1250 (iii) 3700
that surrounds and
Mantle spins around the
inner layer

D. The solid, 4. Iron and Nickel. Extremely hot but (d) 2900 (iv) 2600
innermost part of under too much pressure to exist as a
Crust
the earth liquid.


UN-MIXING THE TABLE

Answers Inner core ____ ____ ____ ____
Outer core ____ ____ ____ ____
Mantle ____ ____ ____ ____
Crust ____ ____ ____ _____

Now write the correct definitions for Inner core, Outer core, Mantle and Crust in the
space provided (below):

Definitions

The inner core is ______________________________________________________
____________________________________________________________________
The outer core is ______________________________________________________
____________________________________________________________________
The mantle is ________________________________________________________
____________________________________________________________________
The crust is __________________________________________________________
____________________________________________________________________


Reading about: THE STRUCTURE OF THE EARTH

Geophysics, which studies the physics of the Earth, has led to many significant discoveries about
the Earth and its make-up. Seismologic studies of the Earth have uncovered new information about
the interior of the Earth that has helped to give credence to plate tectonic theory.
Geophysical studies have revealed that the Earth has several distinct layers. Each of these layers
has its own properties. The outermost layer of the Earth is the crust. This comprises the continents
and ocean basins. The crust has a variable thickness, being 35-70 km thick in the continents and
5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates. Silicates are
based on the mineral silica, SiO2 which is a major component of sand.
The next layer is the mantle, which is composed mainly of ferro-magnesium silicates. It is about
2900 km thick, and is separated into the upper and lower mantle. This is where most of the internal
heat of the Earth is located. Large convective cells in the mantle circulate heat and may drive plate
tectonic processes.
The last layer is the core, which is separated into the liquid outer core and the solid inner core. The
outer core is 2300 km thick and the inner core is 1200 km thick. The outer core is composed mainly
of a nickel-iron alloy, while the inner core is almost entirely composed of iron. Earth's magnetic field
is believed to be controlled by the liquid outer core. Iron and Nickel are magnetic materials. It is the
motion of these materials that gives the earth its magnetic poles
The Earth is separated into layers based on mechanical properties in addition to composition. The
topmost layer is the lithosphere, which is comprised of the crust and solid portion of the upper
mantle. The lithosphere is divided into many plates that move in relation to each other due to
tectonic forces. The lithosphere essentially floats atop a semi-liquid layer known as the
asthenosphere. This layer allows the solid lithosphere to move around since the asthenosphere is
much weaker than the lithosphere. ---> Hwk sheet p126 “Understanding Science”

MINERALS


ROCKS ARE MADE OF MINERALS

Granite is a rock
Quartz is a mineral

Questions
1. What is a mineral?

2. What is the relationship between a rock and a mineral?


MINERAL
IDENTIFICATION

DESCRIBING MINERALS
Hardness
Colour
Streak
Lustre
Cleavage
Acid reaction
Density
Crystal shape and size

MINERALS AND CRYSTAL STRUCTURE

Crystals have flat faces and sharp edges. If the rock splits (cleaves)
in certain planes then it will be made up of crystals.

Iron pyrite Feldspar

Quartz

Most minerals are in crystal form.
The shape of the crystal reflects the
way that the atoms are packed.
Not all minerals have their atoms
packed into crystals


Crystal shape and size

Hexagonal Triclinic Cubic


WEATHERING


INTERACTIVE
EXERCISE
1

What
has caused these
changes?


What
has caused these
changes?

WAVE ACTION


What
has caused these
changes?

WAVE ACTION

STREAM ACTION


What
has caused these
changes?

WAVE ACTION

STREAM ACTION

WAVE ACTION


What
has caused these
changes?

EARTH

MARS


What
has caused these
changes?

EARTH

MARS

BOTH CAUSED BY WIND


What
has caused these
changes?

ICE AND ROCKS,
FALLING UNDER THE
INFLUENCE OF GRAVITY


What
has caused these
changes?

ALTERNATING HEATING
AND COOLING


What
has caused these
changes?

PLANT ROOTS
GROWING INTO THE
ROCK


What
has caused these
changes?

ACID RAIN


What
has caused these
changes?

When marble contains sulphide minerals and undergoes oxidation, the Iron II will produce rust spots, and the sulfur is converted to
sulphuric acid, which can dissolve calcium. During oxidation Iron II is converted to Iron III.

What
has caused these
changes?

CHEMICAL WEATHERING
(CALLED OXIDATION)

When marble contains sulphide minerals and undergoes oxidation, the Iron II will produce rust spots, and the sulfur is converted to
sulphuric acid, which can dissolve calcium. During oxidation Iron II is converted to Iron III.

Frost Wedging (or Freeze - Thaw)

There often needs to be a repetitive cycle of
freezing and thawing (melting)

Glaciers
Weathering takes place in glaciers but not by
the action of frost because the water is not
freezing and thawing so regularly. Instead
_____________________________________

_____________________________________
_____________________________________

This is the Fox Glacier in New Zealand. The sheet of ice is constantly moving down the mountain side,
breaking off rock as it goes and carrying those pieces down the valley.

WEATHERING SUMMARY
Weathering is the process by which rocks are broken down.
Weathering can be Mechanical or chemical.
Mechanical weathering
• Water can dissolve soluble rock or wear away insoluble rock through the action of
waves, streams or rainfall.
• Wind blows pieces of sand over rocks, wearing away softer rock
• Ice and rocks falling under the influence of gravity can wear away the sides of
mountains forming valleys.
• Alternating heating and cooling can break down rocks over time because the rock
contains different materials that expand differently. This forces the materials apart
and causes the rock to be broken down into smaller pieces.
• Frost action can break up rocks because when water freezes in cracks it expands,
forcing the rock to split.
• Plant roots can grow in rocks and as they do so they can break the rock up into
smaller pieces.
Chemical Weathering
• Acid rain reacts with the calcium in rocks causing them to break down.
• Oxidation occurs when the iron sulphide minerals in marble react with oxygen to
form rust.

EROSION AND ITS AGENTS

Erosion is the transportation of rock, soil, and mineral particles. It is this
transportation that causes material to be worn away. Erosion and weathering often
occur together
Sources of erosion:
Gravity
Water (running water, glaciers, and rain)
Wind
Waves

EXAMPLES

________________ ________________


WEATHERING
INTERACTIVE
2

Type of weathering (Mechanical/Chemical/Biological)
A
B
C
D
E
1.Copy this table into
F the back of your
G
H
book.
I 2.Complete it as you
J
K
view the slides
L which follow
M
N
O
P

Type of weathering - Answers
A Mechanical (wind)

B Mechanical (water)

C Mechanical (Freeze - thaw)

D Chemical weathering (acid rain)

E Mechanical (Alternate heating & cooling)

F Mechanical (Gravity causing Glaciers to scour out valley)

G Chemical (acid rain)

H Mechanical (Gravity causing Glaciers to scour out valley)

I Biological weathering

J Mechanical (Alternate heating & cooling)

K Mechanical (Wave action)

L Chemical weathering

M Biological weathering

N Chemical weathering (acid rain)

O Biological weathering

P Biological weathering

Study the pictures (below) and for each picture state the source/s of erosion
responsible for the observed changes. Explain how the changes occurred

Farmland
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________

Desert rocks
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________

Mountain slopes
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Stream _______________________________________________________

SORTING OUT THE ROCK CYCLE

Reading: Y11 Pathfinder

Choose from the labels (right) to complete the flow chart. • Melting

• Deposition of
sediment

• Burial &
compaction

• Erosion &
transport

• Weathering of
rocks at
surface

• Crystallisation
of magma

• Deformation &
metamorphism

SORTING OUT THE ROCK CYCLE
Cut & paste the picture (below) into your book. Choose
from the labels (right) to complete the flow chart.
• Melting

• Deposition of
sediment

• Burial &
compaction

• Erosion &
transport

• Weathering of
rocks at
surface

• Crystallisation
of magma

• Deformation &
metamorphism

TYPES OF
ROCK

The Taupo volcanic zone includes volcanoes in the
central North Island, Rotorua and the Bay of
Reading about volcanoes Plenty. These volcanoes lie along the edge of the
Pacific and Indo-Australian plates. Because the
oceanic crust of the Pacific plate is sliding under
the Indo-Australian plate, volcanic activity is seen
on the continental crust of the Indo-Australian
plate parallel to the plate boundary.
There are different volcano types in the Taupo
volcanic zone. This is because the different volcano
types are created from magma from different
depths along the subduction zone. The thickness of
magma (how easily it flows) depends on its depth
and temperature.
Basalt volcanoes are formed from the eruption of
thin, runny magma which comes from deep
along the subduction zone where the temperature
is high. This magma also has a low silica
content.

Taupo
Volcanic
Zone


Silica thickens the magma and since the silica content is low the magma that forms basalt volcanoes is thin
and runny. The magma that escapes from the crust to form a Basalt volcano is basic (the opposite to being
acidic) and the eruptions that form the slopes of the volcano are mild.

At the other extreme, if the magma comes from a shallow region of the subduction zone, where the
temperature is much lower, Rhyolite volcanoes are formed. This magma which is at a lower temperature
also has a high silica content and is therefore thicker and reluctant to flow easily. The magma is acidic.
This results in steep sided volcanoes like Mount Tauhara and Mount Maunganui. These mountains were formed
by violent eruptions. Lake Taupo was originally a rhyolite dome volcano. Pressure under the mountain rapidly
dropped after a violent explosion which caused the crust to collapse. This formed a caldera. The explosion was
so violent that the ash turned the sky red over Rome and China. The crater that remained filled with water to
form a large lake.

Andesite volcanoes are formed from magma which has a thickness, silica content and acidity which is
somewhere between the basic magma of basalt volcanoes and the acidic magma of rhyolite volcanoes.


Notes to copy ROCK TYPES - FORMATION OF
Igneous rocks
When a volcano erupts, the magma reaches the surface as lava. Lava cools to form
rocks called igneous rocks. Igneous rocks contain crystals which are the result of the
cooling process. There are two types of igneous rocks. Igneous volcanic (extrusive)
rocks form when lava cools rapidly on or near the surface. Igneous plutonic (intrusive)
rocks form when lava cools slowly under the ground. When lava cools quickly, the
crystals are small (as they are in basalt). Slow cooling results in larger crystals to
produce rocks like granite.

Obsidian is an exception. It cools rapidly but without crystal growth. Air can also be
trapped in the lava as it cools rapidly (to form rocks like pumice or scoria).

acidity of Examples of rocks that
Volcano type Shape Silica content
lava form
Rhyolite & Pumice
Rhyolite
(volcanic)
dome
Granite (plutonic)

Andesite (volcanic)
Andesite cone
Diorite (plutonic)

Basalt & scoria (volcanic)
Basalt
Gabbro (plutonic)


Igneous rocks
When a volcano erupts, the magma reaches the surface as lava. Lava cools to form
rocks called igneous rocks. Igneous rocks contain crystals which are the result of the
cooling process. There are two types of igneous rocks. Igneous volcanic (extrusive)
rocks form when lava cools rapidly on or near the surface. Igneous plutonic (intrusive)
rocks form when lava cools slowly under the ground. When lava cools quickly, the
crystals are small (as they are in basalt). Slow cooling results in larger crystals to
produce rocks like granite.

Obsidian is an exception. It cools rapidly but without crystal growth. Air can also be
trapped in the lava as it cools rapidly (to form rocks like pumice or scoria).

acidity of Examples of rocks that
Volcano type Shape Silica content
lava form
Rhyolite & Pumice
Rhyolite
acidic High (volcanic)
dome
Granite (plutonic)

Andesite (volcanic)
Andesite cone intermediate moderate
Diorite (plutonic)

Basalt & scoria (volcanic)
Basalt basic low
Gabbro (plutonic)


ROCKS FROM RHYOLITE VOLCANOES

Rhyolite

Pumice

Granite


ROCKS FROM ANDESITE VOLCANOES

Andesite

Diorite

http://images.google.com/imgres?imgurl=http://geology.com/rocks/pictures/andesite.jpg&imgrefurl=http://geology.com/rocks/igneous-
rocks.shtml&usg=__sMutH3Cxn_0d-
JmbYqEBZ1VRir4=&h=420&w=560&sz=46&hl=en&start=3&um=1&tbnid=7zd20fQWorrOSM:&tbnh=100&tbnw=133&prev=/images%3Fq%3Dandesite%26hl
%3Den%26client%3Dsafari%26rls%3Den%26sa%3DN%26um%3D1

ROCKS FROM BASALT VOLCANOES

Basalt

Scoria
Gabbro

http://images.google.com/imgres?imgurl=http://geology.com/rocks/pictures/andesite.jpg&imgrefurl=http://geology.com/rocks/igneous-
rocks.shtml&usg=__sMutH3Cxn_0d-
JmbYqEBZ1VRir4=&h=420&w=560&sz=46&hl=en&start=3&um=1&tbnid=7zd20fQWorrOSM:&tbnh=100&tbnw=133&prev=/images%3Fq%3Dandesite%26hl
%3Den%26client%3Dsafari%26rls%3Den%26sa%3DN%26um%3D1


Sedimentary rocks

Over time igneous rocks are eroded and the particles (sediments) collect in
rivers and oceans. This material is buried and compacted to form
sedimentary rocks (such as sandstone and mudstone). Sedimentary rocks
can be recognised from the existence of particles such as sand, mud and
pebbles. Sedimentary rocks allow scientists to learn about the environment
that existed when the layers were formed. Fossils are evidence of living things
trapped in the sediments before they became rocks. Scientists can also learn
about climate change from these layers.

Metamorphic rocks

Sedimentary rock that finds itself in deeper, hotter regions of the crust can
change into metamorphic rocks. Metamorphic rocks are formed from
sedimentary rocks that have been subjected to heat and pressure. This occurs
in places where tectonic plates are coming together.

When metamorphic rocks melt they become part of the magma. This leaves
volcanoes as lava which cools to form igneous rocks and the cycle continues.


SEDIMENTARY
ROCK


SEDIMENTARY ROCK FORMATION AND STREAM FLOW RATE

• Sedimentary rocks often have thick layers.

• The layers in the rock reflect the type of sediment.

• A rapidly flowing stream swelled by winter rains can carry large amounts of
coarse sediment with a lot of rotting leaves.

• The same river in summer flows slowly and only carries a small amount of fine
sediment.

• The changing nature of the sediment results in variations of the rock that is
formed - the amount of sediment affects the depth of the layer.

• The size of the grains it contains affects the texture.

• The amount of organic material can change the colour.

Note that:
A layer will not always be the result of the deposition of sediment in a single
season.


ROCK
INTERACTIVE


A
Igneous/Metamorphic/Sedimentary ??


B


C

Schist

D

Granite


E


F


G


H


I

Obsidian


J


K


L


M


ROCK TYPE (Igneous/Metamorphic/Sedimentary)
A Metamorphic

B Igneous

C Metamorphic

D Igneous

E Sedimentary

F Sedimentary

G Metamorphic

H Metamorphic

I Igneous

J Sedimentary

K Igneous

L Metamorphic

M Sedimentary


DESCRIBING
ROCKS


Rhyolite Pumice Granite Obsidian

ROCK
TYPES
IN NCEA
Andesite Diorite Marble Gneiss

Basalt Scoria Gabbro Schist Slate

Conglomerate Sandstone Mudstone Siltstone Limestone Coal

Colour - includes how dark or light the rock is. This is often a result of the silica
content of the rock. Silica, because of its whitish appearance lightens the colour of a
rock depending on the amount of silica present.

Volcanic rocks are classified by their silica content:

Low silica content High silica magma


Colour - includes how dark or light the rock is. This is often a result of the silica
content of the rock. Silica, because of its whitish appearance lightens the colour of a
rock depending on the amount of silica present.

Volcanic rocks are classified by their silica content:

Low silica content High silica magma

Basalt Andesite Rhyolite

Scoria Pumice

Dark rock Light rock

Basic lava Intermediate lava Acidic lava


texture - the feel, appearance or consistency of a surface

(a) Consistency

Obsidian is smooth

(b) Consistency

granular poikilitic sperulitic


Gravel Sized: Conglomerate Sand Sized: Sandstone

Mud Sized:
Mudstone

Siltstone Shale (formed by
mud & clay
pressed together


Grain shape

Conglomerate - rounded grains Breccia - angular grains

Grain size

Gravel 2mm

Sand 1/16 mm

Mud/Silt 1/256 mm

Grain size
Rapidly flowing water transports the largest grains. Heavy particles settle to
the sea floor before smaller particles. Particles are deposited in layers called
strata. The oldest particles are in the lower layers. Evidence of life (fossils) can also
be found in the layers.

Crystal size
Large crystals in rocks are formed when lava cools slowly under the ground.
Small crystals in rocks are formed when lava cools rapidly above the ground.

Practical CRYSTAL SIZE

Aim
Equipment
to demonstrate the effect of rapid formation
Potassium dichromate (solid) and slow formation on crystal size.
Sodium chloride (solid)
Method
water
1. Dissolve a spatula full of sodium chloride in 0.5
microscope slides
mL of water in a test tube. Repeat for
potassium dichromate.
2. Put a couple of drops of each solution on two microscope slides so that you
have 2 slides each with 2 drops of sodium chloride solution and 2 slides, each
with 2 drops of potassium dichromate.
3. Heat 2 slides quickly (over a meths burner) and leave 2 slides overnight to
allow crystals to form slowly.
4. Once formation is complete, compare the slow forming crystals with the fast
forming ones.

Slow formation Rapid formation Slow formation Rapid formation
1 2 3 4


USING A ROCK KEY [p148 “Understanding Science”]

Conglomerate Marble Sandstone Limestone

Slate


PLATE
TECTONICS

MOVING
PLATES


MOVING PLATES ARE CAUSED BY CONVECTION CURRENTS


TRENCHES


VOLCANOES


TRENCHES ARE A RESULT OF SUBDUCTION

Oceanic CRUST A trench Continental CRUST

Subduction zone


RIDGES


RIDGES ARE A RESULT OF MID-OCEANIC SPREADING

Oceanic Crust Oceanic Crust


CONSTRUCTION and DESCTRUCTION


Notes RIDGES and TRENCHES OCCUR TOGETHER

Trench
Ridge Ridge
Continental Plate

Oceanic Plate Oceanic Plate

SPREADING
-->Plate
construction

SUBDUCTION
--> Plate destruction

Magma rises --> cools and expands when it contacts the
ocean --> pushing of the oceanic plates apart --> Ridge
formation as the magma piles up on the edge of each plate

Study the diagrams carefully and use them to write a few sentences which explain how
mid-ocean ridges and trenches are formed:

CONTINENTS RIPPED APART --> THE CREATION OF SEA FLOOR
.. a consequence of the same sea floor
spreading that causes mid-ocean ridges


THE BIRTH OF A SHIELD VOLCANO
.. a consequence of the same sea floor
spreading that causes mid-ocean ridges


PLATE COLLISION WITHOUT SUBDUCTION --> faulting (crack
formation) and folding (mountain formation)


NEW ZEALAND’S SITUATION

2

4

3

(Southern Alps)

1 Mid-oceanic


FOUR TYPES OF PLATE COLLISION
1 Mid-oceanic Magma wells up between two plates that are
Ridge spreading (because of subduction occurring at the
other end of each plate, pulling the plates apart).
The magma piles up on the plate edges. When it
makes contact with the ocean, it cools and solidifies
to create ridges.

2 Subduction Continental CRUST
Subduction occurs when the heavier oceanic crust
Oceanic
zone CRUST
A trench
sinks under the continental crust. Friction between
the two plates and a sinking into a hotter region of
the mantle causes the oceanic plate to melt. Molten
magma seeps through cracks in the continental
Subduction
zone crust to form volcanoes and the friction causes
earthquakes. The colliding plates can also cause
mountain formation. New Zealand lies on subduction
zones.

This is caused by plates colliding directly with
3 Faulting & folding
without subduction each other. There is no subduction. Neither is
there sliding of the plates and causing a
buckling of the crust. Mountain formation occurs
(as in the Southern alps).

4 Faulting This occurs when plates simply slide past each other.
This can lead to earthquakes. The Alpine fault in New
Zealand is an example of such a fault.


PLATE
TECTONIC
THEORY

Notes PLATE TECTONIC THEORY

• 1915 - Alfred Wegener proposed the theory of "continental drift." He suggested that
the continents plowed through crust of ocean basins, which would explain why many
coastlines fit together like a puzzle. He was unable, however to explain why.

• Evidence for some sort of plate/continent movement: Fossils of similar species have
been found on continents that are now separated by great geographic distance.

• Wegener laid the groundwork for the development of modern plate tectonics.

• The plate tectonic theory suggest that the plates float and move on the magma of
the mantle in response to convection currents in the mantle.

http://scign.jpl.nasa.gov/learn/plate2.htm

http://www.tki.org.nz/r/science/science_is/activities/isact_plate_tectonics_02_e.php

THE THEORY OF PLATE TECTONICS


QUESTIONS

1. Describe three New Zealand geological features associated with plate movement.
(i) Southern alps (folding & faulting without subduction) (ii) Alpine fault (faulting)
(iii) Taupo volcanic zone (over a subduction zone)
2. Explain how volcano formation results from plate movement.
Subduction (resulting from a heavier plate pushing and sinking when in contact with a lighter
continental plate) causes the continental crust to weaken. Molten magma under pressure rises
up through the cracks/fissures
3. Discuss the terms “plate destruction” and “plate construction”.
Plate destruction occurs during subduction. The subducting plate sinks into the hotter region
of the mantle and melts. Plate construction occurs where two oceanic plates are moving
apart. Magma that rises to the surface and cools creates new ocean floor
4. Explain why some metamorphic rocks are found high on some New Zealand
mountains.
Metamorphic rocks deep in the crust can be uplifted when folding occurs (in say the
Southern Alps)

5. Explain, in terms of plate movement, the location of the Taupo volcanic zone.
The Taupo volcanic zone is located over a subduction zone. Subduction zones are
areas where the earth’s crust is weakened as a result of a heavier oceanic plate
pushing against a lighter continental plate.


HIDDEN
SECRETS
IN ROCKS

Notes EVIDENCE IN ROCKS

Age of the rock
In any undisturbed strata the oldest rocks are at the bottom and the
youngest are at the top (the law of super imposition)
Carbon dating can be used to determine the age of a rock. This
technique measures the amount of Carbon 14 remaining in a fossil and
because that rate at which this isotope decays is known, the age of the
rock can be calculated.
Unconformities can occur when there is uplifting. An uncomformity is a
time break in sediment deposition. An upper layer/s in the strata
become exposed and erode away to be replaced later by a new layer.
The eroded layer represents a missing geological record.
Life that existed in the past
Fossils are evidence of the existence of life. Fossils in rocks can be
imprints of a once living thing of the remains of a living thing. Fossils
are found in sedimentary rocks which form part of a strata of layers.
They can tell us about the creatures that inhabited the region at a
particular time in the Earth’s history.
Evidence relating to subduction
Metamorphic rocks are formed at plate boundaries where there is
subduction and can tell us how long subduction has been occurring.

The direction of current in a stream
The orientation of shells in sedimentary rock can show us the direction
that water flows in a stream.
The depth of the water
Ripple marks on the rock tell us that the rock was formed in shallow
water.
The speed of the water flow
Large grains are deposited by fast moving water and so where rocks
have large grains the water would have been flowing fast. Slow flowing
water carries finer grains and so rocks with fine grains are found in
places where the water flows slowly.
The length of a stream
Long streams cause particles to become quite rounded so rocks with
rounded particles indicate the location of a long stream.
The salinity of the water at the time
Rocks which contain cubic crystals (salt) indicate the presence of
seawater at the time of formation.

ESA Guide: p302: Activities 23B & 23C


REGIONAL METAMORPHISM

Regional metamorphism covers large areas of continental crust typically associated
with mountain ranges, particularly subduction zones or the roots of previously eroded
mountains.


Geology

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