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. Subduction Zones Strato Volcanoes Rifts Shield 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… Rifts Shield Volcanoes INTERMEDIATE SILICA magma\lava is found at Subduction Zones. This type of magma forms explosive stratovolcanoes… 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.

Rifts… Plate Boundary features: LOW SILICA MAGMA!!! Shield Volcanoes! Ridge or Rise

Subduction Zones… Plate Boundary features: INTERMEDIATE SILICA MAGMA!!! Subduction Zones… Strato Volcanoes! Trench

HOT SPOTS… HAWAII Low Silica magma “burns through” the Plate Plate Boundary features: HOT SPOTS… LOW SILICA!!! Shield Volcanoes! Hot Spot Low Silica magma “burns through” the Plate HAWAII

HAWAII HOT SPOTS leave a “trail” of low silica, Shield volcanoes. Plate Boundary features: HOT SPOTS leave a “trail” of low silica, Shield volcanoes. Pacific Ocean HAWAII

Rows of Stratovolcanoes form along Subduction Zones. Plate Tectonics creates mountains: Rows of Stratovolcanoes form along Subduction Zones.

AND…where continents collide…Rows of Himalayan-like mountains… Plate Tectonics creates mountains: AND…where continents collide…Rows of Himalayan-like mountains… “Old Ocean Rock” Ocean sediments with seashells are folded into towering mountains like the Himalayas and the Alps.

SUBDUCTION ZONES RIFT ZONES

A famous Rift: The Mid-Atlantic Ridge. Iceland is on an active part of The Mid-Atlantic Ridge.

Subduction Zones: Cascades Strato Volcanoes  Andes There are many Subduction Zones are present along much of the West Coast of the Americas.

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

Ocean floor forms continuously… Oldest Ocean floor Youngest Ocean floor

In General… Ocean floor is formed continuously at the rifts. Ocean floor is DESTROYED continuously at the Subduction Zones. The YOUNGEST part of the Ocean Floor is at the RIFTS. (Made today???) The OLDEST part of the Ocean Floor is at the SUBDUCTION ZONES.

In General… The OLDEST parts of the Planet are the CONTINENTS. The Continents are BILLIONS of years old. The YOUNGEST part of the Planet is the Ocean Floor. 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… S …the Magnetic minerals are “Frozen” in place. We can even tell “NORTH” from “SOUTH”…

As the Plates separate… Magnetic Evidence... As the Plates separate… RIFT Magnetic Polarity So as magma rises and cools to form new plate…

Magnetic Polarity reverses… Magnetic Evidence... Magnetic Polarity reverses… RIFT Magnetic Polarity The magnetic minerals that form point North and South…

Magnetic Polarity reverses… Magnetic Evidence... Magnetic Polarity reverses… RIFT Magnetic Polarity

Forming Magnetic “Stripes”. Magnetic Evidence... Forming Magnetic “Stripes”. RIFT Magnetic Polarity

Forming Magnetic “Stripes”. Magnetic Evidence... Forming Magnetic “Stripes”. RIFT Magnetic Polarity

Polar Wandering Curves: As Continents wander…

..and rocks cool… N 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” 