apes unit 01 lecture plate tectonics

7/27/2019 Apes Unit 01 Lecture Plate Tectonics

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Plate Tectonics & Continental Drift Theory

Proposed by German meteorologist Alfred Wegener (1915).

The theory:

~250 million years ago all of Earth's continents had been assembled as a single supercontinent he

called Pangaea (Pangea), which is Greek for "all lands"

Evidence:

"Fit" of continental shelves Similar fossil remains

Similar rock layers in mountain systemsaround the world

Matching layers in glaciers

Wegener's theory was not widely accepted because

No suitable mechanism for continental movement (He proposed the Moon produced a strong tidal influence)


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Sea Floor Spreading1950s were a time of extensive & detailed mapping of ocean floors

Led to the discovery of: BIG mountain ranges under Atlantic, Pacific & Indian Oceans

(Shallow areas in middle of ocean!)

Rift valleys along each mountain crest

Deep ocean trenches near continental land masses

Which the new info H.H. Hess (American geologist) proposed hypothesis of sea floor spreading:

Mid-ocean ridges are the site of active volcanic eruptions.

Youngest rocks at mid-ridge; get older on either side of the ridge

Age of rocks increases to a maximum of approximately 175 million years in the North Atlanticnear the coasts of Europe and North America.


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Paleomagnetisn & Magnetic AnomaliesA compass uses the Earth's magnetic field to point a magnet north

A million years ago, compasses would have pointed south Before that, North, and before that South???

Why the change?

Earths magnetic field flips direction from time to time.

It does not flip at regular intervals.

"normal" (the same direction

as now) for 200,000 yrs,

"reversed" (the opposite

direction) for 300,000 years

normal for 50,000 years

reversed for 190,000 years

AND NOW normal for

730,000 years.

How do we know?

Earth is a huge magnet, with

an iron & nickel core

(remember Earths formation with Theia)

When new rock forms, the minerals align with Earth's magnetic field

The direction of the Earth's magnetic field is recorded in the polarity of rocks that contain iron


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Plate TectonicsWhat does it mean?

Earth'splatesare made of lithosphere (rigid crust)Tektonis Greek for carpenter, or builder

Plate tectonicsrefers to the building of mountains and other large-scale structures using the earth's

lithosphere

The earth's surface iscovered with thin plates

that

Are irregularly

shaped

Move independently

from one another

Move in different

directions

Often meet

resulting in bumping,

jostling and slidingwhich ruptures rock,

causing an

earthquake.

Therefore, looking at earthquake activity around the world (shown in RED) should help us to findthe edges of these plates, and thus to create a plate boundary map.


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Tectonic Plates of the Earth
http://upload.wikimedia.org/wikipedia/commons/8/8a/Plates_tect2_en.svg


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Plate Tectonics, a

Theory that ExplainsScientific Observations.


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Converging Ocean & Continental Plate Boundaries

Distinctive feature:

Deep sea trenches adjacent to chains of volcanoes (The Mariana Trench off the coast of Japan is theworlds deepest at around 35,994 ft deep.)

Converging plate boundaries are common around the Pacific Rim as strings of islands such as

Japan and the Philippines, or along the edges of continents, as in Central and South America.

Subduction Zone

Oceanic plate is thin and dense relative to continental plate.

Oceanic plate bends beneath continental plate forming trench.

In the mantle the plates melt and rise to the surface again, forming the chains of volcanoes.


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Converging Continental Plate BoundariesConvergingContinental Plates built the Himalayas

Collision course:

Indian plate is moving northward and colliding with the Asian plate.

Why do mountains form?

Both Indian and Asian plates are made of continental crust Plates are thick and have a low-density-- NO SUBDUCTION.

The plates buckle and bend, creating a thick and deformed region of continent. (Himalayas!)

The collision is accompanied by many earthquakes.


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Divergent Plate Boundaries

Distinctive topographic features:

The mid-ocean ridges occur where two oceanic plates depart

Many mid-ocean ridges have an axial rift valley--a deep

canyon that runs along the crest of the ridge.

Where continental plates separate there are also rift valleys.

TheEast African Rift Zoneis a good example of divergingcontinental plates.


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Transform Boundaries

Occurs where two plates move laterally past each other.

Generates great shear forces leading to frequent earthquakes.

Distinctive features:

The landscape is different on either side of the

There is a topographic mismatch that marks major transform faults.

San Andreas Fault:

The San Andreas fault from space and in digital topography.


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Types of Faults


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Types of Faults


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Types of Stress & Resultant Faulting


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Hot SpotsHot spots are hot magma built up in the Earth's mantle.

Magma erupts up through the crust as lava & creates volcanoes.

The plates move right over the hot spot, which doesn't move.

This causes volcanic chains to form. The islands slowly erode

as the volcanoes move further from the hot spot!

Hot spots are usually in the middle of a plate, and also, they are

usually in the ocean. . .except Yellowstone & many places in Africa. Why is this?

In the case of the Hawaiian hot spot, the volcanic chain stretches 5000 miles, all the way to Alaska.

The newest probable Hawaiian island, known already asLoihi, is still considered a seamount, is

3000 ft. below sea level and wont

beak the surface for another

18,000 years or so. Assuming

there is still an entity known as

The United States the island chain

of Hawaii will have a new island.

World Wide known Hot Spots


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Plate Boundary Summary


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Plate Boundary San Francisco Bay AreaIn the Bay Area, it is not a question of If but When?

Will you and your family be prepared?


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What will the Earth look like in the future?

Will Pangaea reform?

Scientists use geological clues to figure out past movements of the continents,

Make an educated guess of how the continents are going to move hundreds of millions of years

into the future

One Scientist's Prediction:

Africa is likely to continue its northern movement, closing the Mediterranean and driving up a huge

mountain range in southern Europe.

Australia is likely to merge with the

Eurasian continent. Australia is

moving north, and is already colliding

with the southern islands of SoutheastAsia

Meanwhile, the Americas will be

moving further away from Africa and

Europe as the Atlantic Ocean steadilygrows.

If a subduction zone starts on one side

of the Atlantic, it will start to slowly drag the sea floor into the mantle. If this happens, the ridge

where the Atlantic sea floor spreads will eventually be pulled into the Earth. The widening willstop, and the Atlantic will begin to shrink.

apes unit 01 lecture plate tectonics

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