Features of Plate Tectonics
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Transcript of Features of Plate Tectonics
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12.2
Features of Plate Tectonics
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OVERVIEW
There is lots of evidence that the Earth’s interior is NOT simply a solid ball of rock: Earthquakes Volcanoes Mountains
When the Earth cooled, light elements/materials (ex. silicon and oxygen) floated to the top forming the crust. Earth is made up of 4 layers with distinct characteristics.
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I. TECTONIC PLATES
The outer layer of Earth is made up of several large, rigid but mobile chunks of rock Known as plates or tectonic plates
Lithosphere: formed by tectonic plates in the crust and uppermost mantle Ranges in thickness from 65-100km 12 major plates and several smaller ones
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There are 2 types of plates: Oceanic Plates – contain dense rock basalt Continental Plates – contain large amount
of granite
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II. CROSS-SECTION OF EARTH
Use page 519 in your textto complete the chart in your notes!
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III. PLATE MOTION
Asthenosphere: found below the lithosphere – a partly molten layer in the upper mantle Varied temperature throughout layer due to
radioactive elements (ex. uranium) and radioactive decay
Heated particles have more kinetic energy causes a convection current as the hotter/less dense material rises then cools and sinks
Mantle convection hypothesized as a leading factor in plate movement.
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Rising currents of magma will eventually reach the Earth’s surface at spreading centres
Oceanic Ridge (or spreading ridge): a spreading centre that occurs in the ocean
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Rift Valley: a spreading centre that occurs on land less common
Ridge Push: (1) Magma reaches the surface and cools, creating “new rock”; (2) new rock pushes older material away, forcing plates away from the ridge
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Subduction: a dense ocean plate hits a continental plate heavy ocean plate will dive deep under the lighter continental plate Thought to contribute to plate motion
Subduction Zones: areas generally experience large earthquakes and volcanic eruptions
Slab Pull: as the edge of a tectonic plate subducts deep into the mantle, it pulls the rest of the plate with it
Convection currents, ridge push, and slab pull helps keep tectonic plates in motion!
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IV. PLATE INTERACTIONS
Plate Boundary: a region where 2 tectonic plates are in contact
Plate interaction is important in the geological and biological of Earth. There are 3 main types of plate interactions: Divergence (moving apart) Convergence (moving together) Transform (sliding by)
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The way that plates interact depends on 2 factors: Type of plate Direction of plates movement (relative to
one another)
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DIVERGENT PLATE BOUNDARIES
Divergent Plate Boundaries: areas where tectonic plates are spreading apart
Diverging Plates: plates that are spreading apart
Example: the Mid-Atlantic Ridge System of spreading ridges separating the
Americas from Africa, Europe, and Asia About 16 000km long (largest mountain range
with greatest amount of volcanic activity) Sea-floor spreading causes plates to separate
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CONVERGENT PLATE BOUNDARIES
Convergent Plate Boundary: occurs where tectonic plates collide
Converging Plates: plates that collide
There are 3 types of converging plates: Oceanic-Continental Plate Convergence Oceanic-Oceanic Plate Convergence Continental-Continental Plate
Convergence
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1. Oceanic-Continental Plate Convergence When a dense oceanic plate collides with a
continental plate oceanic plate forced to slide under the continental plate
Trench: a deep underwater valley formed where plates make contact
Large pieces fall off and melt, crystallizing into large rock masses below the continental plate
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Magma can force its way up , creating cone-shaped volcanoes Ex. off the coast of North America (Juan de Fuca
Plate and North American Plate) Cascadian subduction zone
Volcanic Belt: a long chain of volcanoes Collision creates mountain ranges as
continental rock crumples and folds (ex. Coast and Cascade Mountains)
If plates remain stuck in place, pressure builds and can result in earthquakes
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2. Oceanic-Oceanic Plate ConvergenceColliding causes one plate to be denser than
the other the denser one slides deep into the mantle
May produce a long chain of volcanic islands called a volcanic island arc
Ex. islands of Japan, Indonesia, and Aleutian Islands Regions experience earthquakes
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3. Continental-Continental Plate ConvergenceSubduction doesn’t happen due to similar
densities Edges will fold and crumple, forming
mountain ranges Ex. Himalayas caused by Indian continent
hitting Asian continent
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TRANSFORM PLATE BOUNDARIES
Transform Plate Boundaries: usually near ocean ridges where convection currents cause tectonic plates to slide past each other No volcanoes or mountains form Earthquakes and faults can result
Faults: breaks in rock layers due to movement on sides
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Transform Fault: a fault that occur at a transform plate boundary Ex. San Andreas Fault (California) due to
oceanic Pacific Plate sliding past continental North American Plate