Areas of Interest Plate Tectonics Plate Boundaries Causes

Areas of Interest Plate Tectonics Plate Boundaries Causes of Plate Tectonics Evidences Earth Tectonic Plates

Plate Tectonics

§ Plate tectonics (from Greek tektōn "builder") is a theory of geology that has been developed to explain the observed evidence for large scale motions of the Earth's lithosphere § The outermost part of the Earth's interior is made up of two layers: above is the lithosphere, comprising the crust and the rigid uppermost part of the mantle. Below the lithosphere lies the asthenosphere

§ The lithosphere is broken up into what are called tectonic plates § The lateral movement of the plates is typically at speeds of 0. 66 to 8. 50 centimeters per year § This movement is caused by convection current in the mantle

Mid-Atlantic Ridge moves as fast as fingernails grow

Continental Drift Theory

Super-Continent PANGAEA

Sea-Floor Spreading

Atlantic 65 m. y. ago

Present Day Atlantic

Continental Drift + Sea Floor Spreading = Plate Tectonics

These plates move in relation to one another at one of three types of plate boundaries: convergent or collision boundaries, divergent or spreading boundaries, and transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries

Types of plate boundaries Three types of plate boundaries exist, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are: 1. Transform Plate Boundaries 2. Divergent Plate Boundaries 3. Convergent Plate Boundaries

The Earth’s Plates

Plate Boundaries and Earthquakes

1. Transform boundaries Transverse bounaries occur where the plates slide laterally past one another The San Andreas Fault in California is one example. Other examples of transform faults include the Alpine Fault in New Zealand the North Anatolian Fault in Turkey. Volcanoes are rare but earthquakes are common.

San Andreas Fault, CA

2. Divergent Boundaries § Boundary between two plates that are moving apart or rifting § RIFTING causes SEAFLOOR SPREADING

Features of Divergent Boundaries § Mid-ocean ridges § rift valleys § fissure volcanoes

Bridge across the Álfagjá rift on the Reykjanes peninsula in southwest Iceland, the boundary of the Eurasian and North American continental tectonic plates.

3. Convergent Boundaries § Boundaries between two plates that are colliding § There are 3 types…

Type 1 § Ocean plate colliding with a less dense continental plate § Subduction Zone: where the less dense plate slides under the more dense plate § VOLCANOES occur at subduction zones

Type 2 § Ocean plate colliding with another ocean plate § The less dense plate slides under the more dense plate creating a subduction zone called a TRENCH

Type 3 § A continental plate colliding with another continental plate § Have Collision Zones: § a place where folded and thrust faulted mountains form.

Convection Currents § Hot magma in the Earth moves toward the surface, cools, then sinks again. § Creates convection currents beneath the plates that cause the plates to move.

What Drives the plates?

The Plate Tectonics Model

Evidence for Continental Drift I. Early Evidence A. Puzzle-like fit of the continents B. Fossil clues A. Mesosaurus B. Glossopteris C. Plants C. Climate clues A. Glaciers B. Glacial deposits D. Rock clues

A. Puzzle-like fit of the Continents • The edges of some continents look as if they would fit together like a puzzle.

Coast Line Fit: Africa South America

Fit of Continents Across the Atlantic

B. Fossil Clues: Mesosaurus § A freshwater swimming reptile § Fossils found in South America and Africa. § Wegener thought that this reptile lived on both continents when the continents were connected.

Fossil Clues: Glossopteris § Fossil Fern § Found in Africa, Australia, India, South America and Antarctica. § Wegener believed that all these areas were connected.

Ancient Fossils: Plants and Dinosaurs

Climate Clues: Glacial Deposits § Glacial deposits and grooved bedrock found in southern areas of South America, Africa, India, and Australia. § Indicates that these continents were once covered with glaciers. § Wegener believed that these continents were covered with ice near Earth’s South Pole at one time.

C. Climatic Clue : Ancient Glaciations

Present Glaciations

Rock Clues § Similar rock structures are found on different continents. § Mountains found in the eastern U. S. are similar to those found in Greenland western Europe. § The clues found in rocks, support the idea that continents were connected when these rock structures formed.

Rocks Clues : Ancient Mountains

Present Mountains

Major Plates The main plates are: • African Plate covering Africa - Continental plate • Antarctic Plate covering Antarctica - Continental plate • Australian Plate covering Australia (fused with Indian Plate between 50 and 55 million years ago) - Continental plate • Eurasian Plate covering Asia and Europe - Continental plate • North American Plate covering North America and north -east Siberia - Continental plate • South American Plate covering South America Continental plate • Pacific Plate covering the Pacific Ocean - Oceanic plate

Minor Plates The minor Plates are: • • Caribbean Plate Arabian Plate Cocos Plate Juan de Fuca Plate Nazca Plate Philippine Plate Scotia Plate

Questions. . . § What is theory of plate tectonics? § What is the lithosphere? § What is the asthenosphere? § What is the connection between the two? § What are the two types of plates?

Questions. . . § What are three types of boundaries? § What direction do plates go for each? § Which boundary has a subduction zone…what occurs at a subduction zone?

Questions. . . § What causes plates to move? § How is a convection current formed?

What is the Lithosphere? § The crust and part of the upper mantle = lithosphere § 100 km thick § Less dense than the material below it so it “floats”

What is the Asthenoshere? § The plastic layer below the lithosphere = asthenosphere § The plates of the lithosphere float on the asthenosphere

Causes of Plate Tectonics

2 Types of Plates § Ocean plates - plates below the oceans § Continental plates - plates below the continents

Andes Mountains, South America

How Plates Move

Aleutian Islands, Alaska

Benioff’s Interpretation Updated

Crust Go? Hugo Benioff, 1954

Where the Plates Meet

Hot Spots: Hawaii

Brief History of Plate Tectonics § Idea of Continental Drift began to form in 1830’s when the shapes of the continents across the Atlantic were known § Alfred Wegener was the first one to systematically expound the idea § Lack of reliable data prevented the acceptance of the such model until its revival in early 1960’s

Rates of Plate Motions § The relative plate motion rates vary from about 2 cm to over 10 cm/yr § Average rate: about 5 cm/yr or as fast as your finger nail growth § San Andreas – average rate § Pacific Plate near Japan – 10 cm/yr

Scientists Reject Wegener’s Theory § Wegener provided more than evidence for his theory. § He attempted to explain how drift took place. § Unfortunately, Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents. § Therefore, scientists rejected his theory.

Climate Clues § Fossils of warm weather plants were found on islands in the Arctic Ocean. § Wegener believed that these islands drifted from tropical regions.