Embed Size (px)
Citation preview
Plate Tectonics:It started with 4 important observations:
1. Continental Fit:
South America and Africa in particular seemed to “fit together”.
Plate Tectonics:It started with 4 important observations:
2. Similar Fauna and Flora:
Fossils of the same plants and animals are found on several continents.
This might not matter” if they were birds or fish; THEY could travel between continents, but... we’ve found fossils of animals and plants that could NOT cross oceans!
Plate Tectonics:It started with 4 important observations:
3. Similar rock sequence and structures:
Half of a mountain range on one continent…half on another!
Plate Tectonics:It started with 4 important observations:
4. Ancient Climate Patterns:
Glaciers in Africa and South America when Europe and North America had tropical climates.
How could these places have such contradictory weather conditions at the same time? What if the continents themselves moved around?
Plate Tectonics:
1. Continental Fit:
2. Similar Fauna and Flora:
3. Similar rock sequence and structures:
4. Ancient Climate Patterns:
The Basic Concept:
Plates are formed at the Rifts…
Plates are destroyed at Subduction Zones…
The Continents ride on top of the plates…
Rift
Subduction Zone
Plate Boundaries
Plate Boundaries are marked by certain features:
1. Volcanoes…
The TYPE of volcano depends on the type of Plate Boundary.
Rifts
Shield Volcanoes
Subduction Zones
Strato Volcanoes
We will discuss more about volcanoes types later…
But briefly… LOW SILICA magma\lava is found at Rifts.
This type of magma forms “quiet” erupting shield volcanoes…
INTERMEDIATE SILICA magma\lava is found at Subduction Zones.
This type of magma forms explosive stratovolcanoes…
Rifts
Shield Volcanoes
Subduction Zones
Strato Volcanoes
Plate Boundaries are marked by other features:
2. Earthquakes…
Earthquakes differ according to type of Plate Boundary.
Rift Zones have shallow Earthquakes…
Subduction Zones have deep
AND shallow Earthquakes.
Plate Boundary features:
Rifts…LOW SILICA MAGMA!!!
Ridge or Rise
Shield Volcanoes!
Strato Volcanoes!
Plate Boundary features:
Subduction Zones…
INTERMEDIATE SILICA MAGMA!!!
Trench
LOW SILICA!!!
Shield Volcanoes!
Plate Boundary features:
HOT SPOTS…
Hot Spot
HAWAIILow Silica magma “burns through” the Plate
Plate Boundary features:
HOT SPOTS leave a “trail” of low silica, Shield volcanoes.
HAWAII
Pacific Ocean
Plate Tectonics creates mountains:
Rows of Stratovolcanoes form along Subduction Zones.
AND…where continents collide…Rows of Himalayan-like mountains…
Plate Tectonics creates mountains:
“Old Ocean Rock”
Ocean sediments with seashells are folded into towering mountains
like the Himalayas and the Alps.
RIFT ZONESSUBDUCTION ZONES
A famous Rift: The Mid-Atlantic Ridge.
Iceland is on an active part of The Mid-Atlantic Ridge.
Subduction Zones:
Subduction Zones are present along much of the West Coast of the Americas.
Andes
Cascades
Strato Volcanoes
There are many
Additional Evidence: Age of the Ocean floor.
When the Atlantic Rift formed… Ocean floor formed…
How old is the Ocean floor?
When continents separate…
Ocean floor forms continuously…
RIFT
Ocean floor forms continuously…
RIFT
Ocean floor forms continuously…
RIFT
Oldest Ocean floor Oldest Ocean floor
Youngest Ocean floor
Ocean floor forms continuously…
In General…
Ocean floor is formed continuously at the rifts.
The YOUNGEST part of the Ocean Floor is at the RIFTS. (Made today???)
Ocean floor is DESTROYED continuously at the Subduction Zones.
The OLDEST part of the Ocean Floor is at the SUBDUCTION ZONES.
In General…
The YOUNGEST part of the Planet is the Ocean Floor.
The OLDEST parts of the Planet are the CONTINENTS.
The Continents are BILLIONS of years old.
The Ocean floor is (at most) 200 million years old.
AND… Parts of it formed today!
The POLARITY of the Earth’s Magnetic Field reverses fairly often, but irregularly…
N
S
Magnetic Evidence…
When magma cools…
Magnetic minerals form…
When the rock solidifies…
…the Magnetic minerals are “Frozen” in place.
We can even tell “NORTH” from “SOUTH”…
N
S
Magnetic Evidence...
Mag
netic
Pola
rity
As the Plates separate…
RIFT
So as magma rises and cools to form new plate…
Magnetic Evidence...
Mag
netic
Pola
rity
Magnetic Polarity reverses…
RIFT
The magnetic minerals that form point North and South…
Magnetic Evidence...
Mag
netic
Pola
rity
Magnetic Polarity reverses…
RIFT
Magnetic Evidence...
Mag
netic
Pola
rity
Forming Magnetic “Stripes”.
RIFT
Magnetic Evidence...
Mag
netic
Pola
rity
Forming Magnetic “Stripes”.
RIFT
Polar Wandering Curves:
As Continents wander…
N..and rocks cool…
Magnetic minerals point toward magnetic North.
N..as Continents continue to move…
Magnetic minerals in YOUNGER rocks point to Magnetic North…from a different location!
“Weird” additional evidence!
“Bugs on the Windshield!”
As Continents move…
…they run into things!
Small pieces of land are “squished” onto the main Continent!
These are called “Displaced Terranes”!
They’re sort of like “bugs on the windshield”
