Oceans And Continents

Front 1

Fold mountains

Back 1

Rockies, Andes, Himalayas, Alps

Compressional stress

Convergent plate boundaries

Shallow and intermediate earthquakes.

They fit together and have the same age and same rock type suggesting they were once one belt.

Front 2

Graben

Back 2

Strip of crust that has slipped down due to two inward dipping normal faults.

Start of the continent splitting to form a new ocean.

Shallow focus earthquakes are common.

Front 3

Cratons

Back 3

Made of Gniess

Very old

Distant from plate boundaries and are aseismic.

Flat due to long period of erosion.

Fit together to provide evidence for continental drift.

Front 4

Continental shelf, slope and abyssal plain

Back 4

Slope=4°, 200-1500/3500Km, sediment are transported down the slope by turbidity currents.

Plain=3-5Km, flat and underlain by oceanic crust, covered in fine grained pelagic sediments composed of the skeletons of microscopic planktonic organisms, aseismic.

Shelf=continental crust, covered in beds of clastic sediment, around 200M deep.

Front 5

Trenches

Back 5

Submarine valleys

11Km deep

150Km wide

100s of Km long

Front 6

Seamounts and guyots

Back 6

Seamounts=submarine basalt volcano, rises up to 1000m off sea floor without reaching sea level.

Guyot=seamount with flat, eroded top.

Front 7

MOR

Back 7

Middle is an axial rift

Submarine eruptions of basalt occur

Occur at divergent plate boundaries

Shallow earthquakes occur

Front 8

Continental drift

Back 8

Super continent=Pangea

North=Laurasia

South=Gandwanaland

Fit of the land=deposition and erosion and sea level change.

Distribution of fossils=Glossopteris, fossils found across different continents, suggests when pangea existed animals could disperse leaving their fossils on different continents.

Rock types=certain rocks form in particular environments and environments are indicative of climate, which is indicative of latitude. Limestone that contains corals also indicate tropical climates, has been found in the UK, this implys it must have drifted north overtime.

Front 9

Glaciation

Back 9

Glaciers scrape sediment off the ground and carries it along. Pebbles and sand freezes into base of glacier- becoming like sandpaper. Protruding rock pieces scratch underlying rock (striations)

Striations=direction of flow. The orientation of striations match across continents. The deposit is called tillites and they also match across continents.

Front 10

Sea floor spreading

Back 10

Provides the mechanism that allows the continents to move.

SONAR=obtains a bathymetric profile, revealed each ocean basin has a prominent MOR.

Gravity anomaly=mesures small variations in the gravitational field strength, if the rock is dense it will have a positive anomaly, at the axial rift there is a positive anomaly.

Heat flow=at the axial rift where basaltic magma is rising there is a positive heat flow.

Front 11

Fumaroles/Black smokers

Back 11

Cold seawater enters cracks in the crust, which are created by tensional stress.

Water becomes super heated by the magma at MOR.

Water dissolves metals from crust leading to hydrothermal fluid.

Hydrothermal fluid rises through cracks and fissures and cools rapidly against cold sea water.

As it cools it precipitates minerals forming the vent.

Front 12

Age of ocean floor

Back 12

Rocks at MOR are youngest

Oldest rocks are furthest away

Age is symmetric about the axis of the ridge.

Front 13

Magnetic anomalies

Back 13

Symmetric about the ridge

Front 14

Thickness of sediment

Back 14

Furthest away have more sediment because it has had more time to accumulate.

Front 15

Origin of earths magnetic field

Back 15

Outer core is hot and molten

It is hotter nearer the boundary with the inner core.

So convection current occur.

A convecting mass of molten iron will generate electricity.

The generation of electricity induces magnetism, which generates more electricity which generates more magnetism and so on.

This is called the self-exciting dynamo.

The outer core is well above the curie point, which is the temp minerals lose their magnatism.

So if the convecting stops then the magnetic field will stop.

Front 16

Palaeomagnetism

Back 16

Basalt contains a minor amount of magnetite.

Basaltic magma is at 1200° and is way above the curie point.

As it cools it starts to crystallize magnetite. Dipoles of all atoms become parallel with each other and the magnetic field lines at the specific location.

At 350-550°c the dipoles lock into position and the basalt becomes a permanent magnet. The alignment is permanent and is called remnant magnetism.

Basalt provides a record of the orientation of the earths magnetic field lines at the time the rock cooled. This record is palaeomagnetism.

Front 17

Polar wandering

Back 17

Earths magnetic poles appear to move around the globe.

Tracking the position of the poles through time has led to a polar wandering curve, which is a line on a map, which joins up the recorded positions.

Rocks of the same age in Europe and North America suggested the north pole was in two places at once.