PlateTectonics

Greatest Geological Theory in the Past 200 Years

PLATE TECTONICS (def.) The theory that all of the continents were once part of a large land mass called PANGA.

The continents of PANGA split and have drifted away from each other.

The process of splitting apart and drifting has produced the continental shapes we know today.

continents looked like a big jigsaw puzzle.

1912 - Alfred Wegner was the first scientist to

Pulling Apart (accreting boundaries) Mid-Atlantic Ridge

Pushing Together (consuming boundaries) West Coast

Sliding past each other (transforming boundaries)

In the 1960s, scientist found a world wide system of mountains called RIDGES in all of the oceans.

The RIDGES are caused by LAVA rising to the surface from deep within the earth. This creates new crust.

The proof that the seafloor was spreading was based on two discoveries.

First -- The farther away from the center of the ridge -- the older the rock!

Second -- Because the MAGNETISM of the poles has changed direction 9 known times, new rocks, made of Iron during these time periods, would point in the direction of the magnetic pole as the rocks were formed and cooled.

This should leave a MAGNETIC MAP that would be the same on both sides of the RIDGE -- It did!

By Studying a map of the ocean floor, scientist have concluded that the earth is divided into major PLATES that float on top of the mantle.

TRENCHES -- Where plates move toward each other, parts of the crust are being pushed down into the mantle. When this occurs in the ocean, it produces deep TRENCHES.

When one piece of the earths crust is forced under another, it is called subduction.

It is at the point of SUBDUCTION that most of the worlds earthquakes and volcanoes occur.

One of the major results of Plate Movement is the building of mountains.

A. VOLCANIC -- usually located at the point of SUBDUCTION. When the earths crust is pushed down into the mantle, the crust is melted into MAGMA and breaks through the upper plate in the form of LAVA.

Usually located where two continents are being pushed together. This forces the earths crust to crumble..

Examples -- Appalachians in the Eastern U.S. Urials in Russia, Himalayas in Southern Asia and the Alpine Mountains in Central Europe

C. BLOCK-FAULTED MOUNTAINS. These mountains are a result of pressure. As the plates are being pushed or pulled, cracks known as FAULTS occur, resulting in areas slipping up or down.

Examples: Rickeys and Sierra Nevada in the western United States.

D. DOME MOUNTAINS -- resulting from pressure from within the earth that lifts large areas of land.

BATHOLITH to form a smaller area of DOME near the surface. This is called a LACCOLITH. When the land above is eroded away and leaves the rock exposed, an area like Stone Mountain is formed.

Mountain Ranges form at different times because the PLATES are always moving. Some are no longer growing while others are considered young at 70 million years old and are still growing.

* Indicates Mountains that are still growing.

Almost all of the worlds growing volcanic mountains surround the Pacific Ocean. This area is also active in earthquakes. It is called the RING OF FIRE.

Plate movement can account for all of the mountains except ISLANDS not located at the edge of PLATES. Such as the Hawaiian Islands.

These mountains are caused by HOT SPOTS. As the plates move over the HOT SPOT a new island is formed. The old island, no longer growing, will eventually erode away.



	Plate Tectonics Greatest Geological Theory in the Past 200 Years PLATE TECTONICS (def.) The theory that all of the continents were once part of a large land mass called PANGA. The continents of PANGA split and have drifted away from each other. The process of splitting apart and drifting has produced the continental shapes we know today. 1620 - Sir Francis Bacon observed that the continents looked like a big jigsaw puzzle. 1912 - Alfred Wegner was the first scientist to suggest that the continents were moving. The plates are doing one of three things: Pulling Apart (accreting boundaries) Mid-Atlantic Ridge Pushing Together (consuming boundaries) West Coast Sliding past each other (transforming boundaries) The Proof of Plate Tectonics 1. SEAFLOOR SPREADING In the 1960s, scientist found a world wide system of mountains called RIDGES in all of the oceans. The RIDGES are caused by LAVA rising to the surface from deep within the earth. This creates new crust. The proof that the seafloor was spreading was based on two discoveries. First -- The farther away from the center of the ridge -- the older the rock! Diagram of Sea Floor Spreading Second -- Because the MAGNETISM of the poles has changed direction 9 known times, new rocks, made of Iron during these time periods, would point in the direction of the magnetic pole as the rocks were formed and cooled. This should leave a MAGNETIC MAP that would be the same on both sides of the RIDGE -- It did! Diagram of Magnetic Field Map PLATE MOVEMENT (Continental Drift) By Studying a map of the ocean floor, scientist have concluded that the earth is divided into major PLATES that float on top of the mantle. Diagram of Istosty TRENCHES -- Where plates move toward each other, parts of the crust are being pushed down into the mantle. When this occurs in the ocean, it produces deep TRENCHES. When one piece of the earths crust is forced under another, it is called subduction. It is at the point of SUBDUCTION that most of the worlds earthquakes and volcanoes occur. 2. MOUNTAIN BUILDING One of the major results of Plate Movement is the building of mountains. Mountains are built in one of four ways. A. VOLCANIC -- usually located at the point of SUBDUCTION. When the earths crust is pushed down into the mantle, the crust is melted into MAGMA and breaks through the upper plate in the form of LAVA. Diagram of Subduction B. FOLDED MOUNTAINS Usually located where two continents are being pushed together. This forces the earths crust to crumble.. Diagram of Folded Mountains Examples -- Appalachians in the Eastern U.S. Urials in Russia, Himalayas in Southern Asia and the Alpine Mountains in Central Europe C. BLOCK-FAULTED MOUNTAINS. These mountains are a result of pressure. As the plates are being pushed or pulled, cracks known as FAULTS occur, resulting in areas slipping up or down. Diagram of Block-Faulted Mountains Examples: Rickeys and Sierra Nevada in the western United States. D. DOME MOUNTAINS -- resulting from pressure from within the earth that lifts large areas of land. Diagram of Dome Mountain Example -- Black Hills in South Dakota BATHOLITH to form a smaller area of DOME near the surface. This is called a LACCOLITH. When the land above is eroded away and leaves the rock exposed, an area like Stone Mountain is formed. Diagram of a Laccolith Mountain Ranges form at different times because the PLATES are always moving. Some are no longer growing while others are considered young at 70 million years old and are still growing. *Mountain Range Age (Millions) Type* Cascades * 1 Volcanic Himalays * 25 Folded/Block Alpines * 40 Folded Andes * 70 Volcanic/Folded Rockeys * 70 Block-Fault Sierra Nevadas * 135 Block-Fault Urals 220 Folded Appalachians 225 Folded * Indicates Mountains that are still growing. Almost all of the worlds growing volcanic mountains surround the Pacific Ocean. This area is also active in earthquakes. It is called the RING OF FIRE. Diagram of the Ring of Fire Plate movement can account for all of the mountains except ISLANDS not located at the edge of PLATES. Such as the Hawaiian Islands. Diagram of Hawaiian Islands These mountains are caused by HOT SPOTS. As the plates move over the HOT SPOT a new island is formed. The old island, no longer growing, will eventually erode away. Diagram of Hot Spots Return to Main Page