of 17
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
1/17
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)
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
2/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
3/17
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
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
4/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
5/17
Tectonic Plates of the Earth
http://upload.wikimedia.org/wikipedia/commons/8/8a/Plates_tect2_en.svg7/27/2019 Apes Unit 01 Lecture Plate Tectonics
6/17
Plate Tectonics, a
Theory that ExplainsScientific Observations.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
7/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
8/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
9/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
10/17
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.
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
11/17
Types of Faults
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
12/17
Types of Faults
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
13/17
Types of Stress & Resultant Faulting
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
14/17
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
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
15/17
Plate Boundary Summary
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
16/17
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?
7/27/2019 Apes Unit 01 Lecture Plate Tectonics
17/17
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.