PLATE TECTONIC THEORY

• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.

WEGENER’S CONCEPT OF PANGEA

Alfred Wegener in the early 1900’s proposed the hypothesis that continents were once joined together in a single large land mass he called PANGEA (meaning “all land” in Greek).He proposed that Pangea had split apart and the continents had moved gradually to their present positions - a process that became known as continental drift.

CONTINENTAL DRIFT

According to the hypothesis of continental drift, continents have moved slowly to their current locations.

WEGENER’S EVIDENCE FOR CONTINENTAL DRIFT

Fossils of plants and animals of the

same species found on different

continents.

So basically, plate tectonics is the

modern version of that continental drift

theory by Alfred Wegener

PLATE TECTONICS

 is the scientific theory

that attempts to explain

the movements of the

Earth's lithosphere that

have formed the

landscape features we see

across the globe today.

CONT….

By definition the word "PLATE"

in geologic terms means a

large slab of solid rock.

"TECTONICS" is a part of the

Greek root for "to build" and

together the terms define how

the Earth's surface is built up

of moving plates.

•The Earth’s crust is divided into 15 major plates which are moved in various directions.

•This plate motion causes them to collide, pull apart, or scrape against each other.

CONT….

•Each type of interaction

causes a characteristic

set of Earth structures or

“tectonic” features.•The word, tectonic, refers

to the deformation of the

crust as a consequence

of plate interaction.

LIST OF THE MAJOR PLATES

PRIMARY PLATES

These seven plates comprise the bulk

of the continents and the Pacific

Ocean.

•African Plate

•Antarctic Plate

•Eurasian Plate

CONT…

•Indo-Australian Plate •North American Plate•Pacific Plate•South American Plate

SECONDARY PLATESThese smaller plates are generally not shown on major plate maps, as they do not comprise significant land area.

•Arabian Plate•Caribbean Plate•Cocos Plate•Indian Plate

SECONDARY PLATES•Juan de Fuca Plate

•Nazca Plate

•Philippine Plate

•Scotia Plate

World Plates

What lies beneath the tectonic plates?• Below the

lithosphere (which makes up the tectonic plates) is the

asthenosphere.

• The ASTHENOSPHERE, beneath the lithosphere, is part of the upper mantle and is so hot that it is 1 – 5% liquid. This liquid, usually at the junctions of the crystals, allow it to flow – which is why ‘astheno’ means “weak.” Beneath the asthenosphere is the rest of the mantle, which is completely solid – but can also flow because of the intense temperatures and pressures involved.

2 Types of plates

CONTINENTAL PLATE•Continental plates contain most of the world's land.

OCEANIC PLATE• Oceanic plates are formed under the sea.

•both plates are thinner and denser. As a result, oceanic

crust tends to subduct (sink) below the continental crust

wherever their boundaries meet.

3 Types of Plate Boundaries

• DIVERGENT•CONVERGENT•TRANSFORM

1. DIVERGENT•boundaries are plates that moves away from each other

• As the plates pull apart, hot molten material can rise up this newly formed pathway to the surface - causing volcanic activity.

• If a divergent boundary forms on a continent it is called a RIFT or CONTINENTAL RIFT.

• If a divergent boundary forms under the ocean it is called an OCEAN RIDGE.

• Iceland has a divergent plate boundary running through its middle

Iceland: An example of continental rifting

2.CONVERGENT•Boundariesare the Plates thatMovetowardseach other

3 TYPES OF CONVERGENT BOUNDARY

1.CONTINENTAL-CONTINENTAL COLLISION

2.OCEANIC-CONTINENTAL COLLISION

3.OCEANIC-OCEANIC COLLISION

• Neither side of the boundary wants to sink beneath the other

side, and as a result the two plates push against each other and

the crust buckles and cracks, pushing up high mountain ranges.

1. Continental-Continental Collision

Example: Himalayas as continental crust was pushing

against continental crust the Himalayan mountain belt was

pushed up.

• A.K.A SUBDUCTION ZONE

2. Continent-Oceanic Crust Collision

• Oceanic lithosphere subducts underneath the continental lithosphere

• Oceanic lithosphere heats and dehydrates as it subsides

• The melt rises forming volcanism

• E.g. The Andes

Subduction

• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

• The subducting plate is bent downward to form a very deep depression in the ocean floor called a TRENCH.

• The worlds deepest parts of the ocean are found along trenches.

EXAMPLE : THE MARIANA TRENCH

3. OceanIC-OceanIC Plate Collision

THE MARIANA TRENCH

•are plates that slide past each other.

3. Transform Boundaries

The San Andreas Fault is the most well-known (and most deadly) translational interface. The two plates slides by one another along a large scale fault. Since these are two large pieces of rock, there is a great deal of frictional coupling that occurs. Sometimes the plates get locked in some local region and great deal of strain energy is stored in that region. Eventually, the strain energy builds up to the point where the it is suddenly released which creates a large scale earthquake.

View of the San Andreas transform fault

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