Tectonic plates

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Tectonic plates

WEGENER´S THEORY OF CONTINENTAL DRIFT

Some cientists think continets were imobile, others think move over time.

+THEORY OF CONTNENTAL DRIFT

German geophysicist and meteoroloist, Alfred Wegener was first find proof explain continents (their continental shelf) look like fit together and demostrate continents were joined in the past. He thought continents were floating on the ocean.

1912: he propossed hypothesis that all continents were together as 1 supercontinent (Pangea) and separated by 1 ocean (Panthalassa).

+WEGENER´S EVIDENCE FOR CONTINENTAL DRIFT

*geological evidence: continental shelves fitted together, identical rock and geological structures on both sides.

*Palaeontological evidence: identical fossils on both sides, they couldn´t have cross the ocean.

*Palaenoclimatic evidence: He examined moraines deposited by glaciers on south of Pangea. Identical moraines of the same age.

WEGENR DID NOT FIND EVIDENCE TO EXPLAIN THE MOVEMENT OF THE CONTINENSTS.

THE STRUCTURE AND COMPOSITION OF THE EARTH

+METHODS FOR STUDYING THE EARTH´S INTERIOR

*Core sampling and mining: not very eficient, they drill until 13 km only.

*Studying rocks: natural phenomena, move rocks (interior) to the surface. Erosion and volcanic eruptions.

*Studying metorites and asteroids: Tell the original materials of the Earth.

*Seismic methods: most important, measure seismic waves from earthquakes on seismographs (information about layers).

Waves Origin of the name speed substances they travel movement they provoke

P Primary: first-surface faster solids (faster) and liquids same direction

S Secondary: second-surface slower liquids perpendiculary

+THE COMPOSITION AND DYNAMICS OF THE EARTH

*Compositional layers: crust, matle (upper and lower) and core (outer and inner) separated by seismic discontinuities.

*Physical layers: Lithosphere, asthenosphere, methosphere and endosphere.

+THE CRUST AND THE LITHOSPHERE

lithosphere - rigid, includes crust and a part of the upper mantle, discontinuous layer and broken into peaces (plates).

OCEAN FLOOR

*Trenches: deep channels near continental boundaries or volcanic island arcs. (11 Km)

*Mid-ocean ridge: Underwater mountain range, formed by plate tectonics that have a divergent movement. (long: 60000 Km, wide: 2000 Km)

*Seamounts (island): volcanic landform with pointed top.

*Guyots: volcanic landform with flat top.

*Island arc: curved chains of volcanic islands near trenches.

*Volcanic archipielagos hain of volcanic islands near hot spots.

*Continental slope: area between continental shelf and abyssal plain.

*Abyssal plain: Flat area on the ocean floor. (4 Km)

*Continental sheilf: edge of the continet under water.

*ocean ridge: underwater moutain ridge.

*Rift: Faults in ocean ridge.

*Transforms faults: Fractures in oceanic crust that move horinzontally.

(Sonar: sends sound waves, measures time eco returns)

+COMPOSITION OF THE OCEAN FLOOR

Ocean floor made of volcanic rocks, it has pillow lavas and magmatic rocks. The rocks closest to an ocean ridge were younger than ones away.

THE BIRTH OF PLATE TECTONICS

A network of seismographs was set up around the globe for analysing seismic waves.

+THE DISTRIBUTION OF EARTHQUAKES AND VOLCANOES

Earthquakes are in seismic belts and are abundant in areas of volcanoes. There is a relation between the location of the seismic belts (earthquakes and volcanoes) and trenches and ridges.

+TECTONIC PLATES (a fragment of the lithosphere, each plate is separated by a seismic belt and volcanoes)

*Types of plates (These plates are mobile)

-Size: 8 large plates and many microplates.

-Type of lithospher: Oceanic plates, Continental plates and mixed plates.

(The study of the dynamic nature is called plate tectonics)

+SEA FLOOR SPREADING (dicover by Harry Hess)

The age of rocks depends on their position to the ridge.

*Sea-floor spreading: Plates move apart, magma rises from the mantle and pushes the older lava deposites. Lava cools (rock). As floor expands continents move away each other.

+THE SUBDUCTION OF THE OCAN FLOOR

Oldest part of the ocean bends and sink into the mantle, while oceanic lithosphere is formed at ridges, it is also destroyed at trenches.

*Subduction: process in which oceanic lithosphere moves under the continental lithosphre and goes into mantle.

THE THEORY OF PLATE TECTONICS

*Lithosphere is divided into pieces called plates.

*Most volcanoes and earthquakes caused by internal geological activity of the Earth located at the borders between the plates.

*Plate movement moves the continents.

(Whole lithosphere was contatly moving and not just the continents)

+consecuences:

*Distribution of seismic and volcanic activity.

*Present and previuos distribution of continents and oceans.

*Formation of mountain ranges.

*Distribution of minerals and fossils fuels.

+HOW PLATES MOVE

*ORIGINAL EXPLANATION: Convection currents in asthenosphere caused tectonic plate movement.

*CURRENT EXPLANATION: Lithosphere no just floats ts contributes:

*The force of gravity and the weight of the plate.

Internal heat generates convection currents in mantle combined withgravity and weight of the plate and they move.