The Theory of Plate Tectonics

Scientific precedent: Continental Drift

Alfred Wegener:1915. “The Origen of Continents and Oceans”

Paleolithic evidence

Geological evidence

Paleoclimatic evidence

Continental jigsaw puzzle

•What’s wrong with Continental

Drift?

•How long did we wait for a new

theory?

•How did it come?

During the second half of the 20th century:

• Seismometers network.• Submerged relief of the oceans.•Age of the rocks of the ocean floor.•Paleomagnetism of the ocean floor.•Distribution of earthquakes and volcanos.

Global Tectonics

Main concepts

• The lithosphere is divided into great

blocks.

• Lithosperic plates are dynamic.

• The ocean floor is continually generated

and destroyed.

Main tectonic plates

Types of plate boundaries

• Divergent or constructive boundaries.

• Convergent or destructive boundaries.

• Transform or passive boundaries.

Divergent boundaries

What geological phenomena are likely to occur here?What do you see here? Come on, make the effort!

Would the study of the rock age help?

•Molten material rises up and solidifies on the surface, pushing the 2 plates in opposite directions.

•New lithosphere is being formed here, so:• Do plates increase their size?• Is the Earth’s surface increasing?

Divergent boundaries

RIDGES CONTINENTAL RIFTS

Divergent boundaries can be found on the sea floor or on land.

What is this?

Transform or passive boundaries

• Fractures where 2 plates slide horizontally

against each other.

• Is lithosphere being created here?

• What geological phenomena are expected?

• Do you know any of these transform faults by name?

Passive boundaries

Convergent or destructive boundaries

• Two plates moving towards each other interact.what happens then?

• 3 types according to the composition of the plates in the area of collision:

1. Continental and oceanic.2. 2 oceanic plates.3. 2 continental plates.

Types of destructive boundaries

Could you define subduction?

How do we know this is real?

Depth of hypocentres

The further you go from the trench, the deeper the hypocentres are plane of subduction or plane of Benioff.

Oceanic-Continental

• Oceanic plate subducts under continental.

• Quakes along a sloping plane.

• Andean or marginal mountain ranges with active volcanoes.

Oceanic-Oceanic

• The oldest one subducts. Why?• Friction+high T melt the rocks.•Active volcanoes form an island arc.

Continental-Continental

Continental lithosphere can’t subduct. What now? A mountain range is formed.Earthquakes.What about volcanism?

Types of boundaries. Summary.Type of boundary

Tye of movement

Ocean floor Landform produced

DIVERGENT Separation Creates oceanic lithosphere

Ridges and continental rifts

CONVERGENT Collision Destroys oceanic lithosphere

Trenches, island arcs and mountains

TRANSFORM Lateral displacement

Neither creates nor destroys

Transform faults

The Wilson CycleJohn Tuzo Wilson (1909-1993):• At least, two geological processes of rifting

and reuniting of supercontinents.• This cycle brings together all the phenomena

studied so far.• Can be organised in 3 stages:

1. Continental rifting.2. Expanding ocean.3. Continental collision.

Activity: Organise these images in a cycle.

Continental fragmentation.

Plate dynamics and heat under the continent can fracture the continent.

First, it bulges and breaks, then, it sinks down and a CONTINENTAL RIFT is formed.

Formation of an expanding ocean.

The Atlantic ocean is an example. Its size is increasing steadily due to the production of new oceanic lithosphere.

What’s going on here?

Closing of the ocean basin and continental collision.

The oceanic lithosphere near the edge of the continent fractures and stars to subduct.

Why? Increased density. Weight of sediments.

During the second half of the 20th century:• Seismometers network.•Distribution of earthquakes and volcanos.• Submerged relief of the oceans.•Age of the rocks of the ocean floor.•Paleomagnetism of the ocean floor.•Laser and GPS measurements.

Global Tectonics

The evidence for the theory of plate tectonics

Distribution of erthquakes and volcanoes

Mapping of the submerged relief

Study of the age of the rocks of the ocean floor

Study of the age of the rocks of the ocean floor

Paleomagnetism of the ocean floor

Laser and GPS measurements

Intra-plate phenomena

How do we explain the movement of the plates?

1. Convection Currents.2. Push exerted by new materials in the oceanic

ridges.3. Pull due to the weight of sinking plates in

oceanic trenches.