Plate Tectonics & The Wilson Cycle5

Plate Thickness

Earth's lithospheric plates are 100 to 300 kilometers thick.

Plate Velocity

Plates shift at a very slow pace of 5 to 20 centimeters per year.

Mantle Convection Currents

Hot rock rises and cooler rock sinks, acting as a massive thermal conveyor belt.

Slab Pull

Gravity pulls the dense edge of a subducting oceanic plate down into the mantle.

Divergent Boundaries Motion

Plates pull apart from each other, creating brand-new oceanic crust.

Divergent Boundary Features

Mid-ocean ridges containing a deep central rift valley, volcanism, and shallow earthquakes.

Initial Stage of Rifting Example

The East Africa Rift Valleys.

Juvenile Stage of Rifting Example

The Red Sea.

Mature Stage of Rifting Example

The Atlantic and Indian Oceans.

Iceland Surface Exposure

The Mid-Atlantic Ridge rises completely above sea level here.

Convergent Boundaries Motion

Plates crash together, destroying old oceanic crust as it melts back down.

Oceanic-Continental Collision

The heavy ocean plate subducts beneath the lighter continent, forming volcanic arcs.

Oceanic-Oceanic Collision

The denser ocean plate subducts, creating deep trenches and volcanic island arcs.

Continental-Continental Collision

Low-density continental crust resists subduction, compressing and uplifting massive mountain ranges.

Transform Boundaries Motion

Plate segments horizontally slide past one another where crust is neither created nor destroyed.

Oceanic Transform Faults Example

The Mendocino Fracture Zone and Eltanin Fault.

Continental Transform Faults Example

The San Andreas Fault in California.

Hotspot Definition

Active volcanic zones created by a stationary heat source deep in the mantle.

Hotspot Mechanics

A thermal plume punches through the middle of a moving tectonic plate.

Hawaiian Islands Age Progression

Oldest islands sit to the northwest, while the youngest active islands sit southeast.

Isostatic Sinking

Islands cool, contract, and sink back down into the crust as they leave hotspots.

Continental Hotspot Example

The massive Yellowstone hotspot system.

Wilson Cycle Embryonic Stage

A complex system of linear rift valleys tearing across a continent.

Wilson Cycle Juvenile Stage

Narrow, flooding seas bounded by matching coastlines.

Wilson Cycle Mature Stage

A wide, expanding ocean basin bounded by stable continental margins.

Wilson Cycle Declining Stage

Island arcs and deep trenches form around a shrinking ocean basin.

Wilson Cycle Terminal Stage

Narrow, irregular seas closed in by young, growing mountains.

Wilson Cycle Suturing Stage

Complete ocean closure resulting in massive mountain belts.

Continental Drift Hypothesis Criticisms

Alfred Wegener's hypothesis was dismissed primarily because it lacked a working physical mechanism.

Deepest Hole Drilled

The Kola Well in Russia, reaching 12.2 kilometers deep.

Seafloor Spreading Theory

Proposed by Harry Hess and Robert Dietz as the driving mechanism for plate tectonics.

Ocean Floor Magnetic Anomalies

Rocks record Earth's magnetic polarity changes as hot lava cools at ridges.

Richter Scale

A logarithmic scale measuring earthquake magnitude and frequency.

Plate Thickness

Earth's lithospheric plates are $100$ to $300\,\text{km}$ thick.

Plate Velocity

Plates shift at a very slow pace of $5$ to $20\,\text{cm/year}$.

Mantle Convection Currents

Hot rock rises and cooler rock sinks, acting as a massive thermal conveyor belt.

Slab Pull

Gravity pulls the dense edge of a subducting oceanic plate down into the mantle.

Divergent Boundaries Motion

Plates pull apart from each other, creating brand-new oceanic crust.

Divergent Boundary Features

Mid-ocean ridges containing a deep central rift valley, volcanism, and shallow earthquakes.

Initial Stage of Rifting Example

The East Africa Rift Valleys.

Juvenile Stage of Rifting Example

The Red Sea.

Mature Stage of Rifting Example

The Atlantic and Indian Oceans.

Iceland Surface Exposure

The Mid-Atlantic Ridge rises completely above sea level here.

Convergent Boundaries Motion

Plates crash together, destroying old oceanic crust as it melts back down.

Oceanic-Continental Collision

The heavy ocean plate subducts beneath the lighter continent, forming volcanic arcs.

Oceanic-Oceanic Collision

The denser ocean plate subducts, creating deep trenches and volcanic island arcs.

Continental-Continental Collision

Low-density continental crust resists subduction, compressing and uplifting massive mountain ranges.

Transform Boundaries Motion

Plate segments horizontally slide past one another where crust is neither created nor destroyed.

Oceanic Transform Faults Example

The Mendocino Fracture Zone and Eltanin Fault.

Continental Transform Faults Example

The San Andreas Fault in California.

Hotspot Definition

Active volcanic zones created by a stationary heat source deep in the mantle.

Hotspot Mechanics

A thermal plume punches through the middle of a moving tectonic plate.

Hawaiian Islands Age Progression

Oldest islands sit to the northwest, while the youngest active islands sit southeast.

Isostatic Sinking

Islands cool, contract, and sink back down into the crust as they leave hotspots.

Continental Hotspot Example

The massive Yellowstone hotspot system.

Wilson Cycle Ocean Phases

The Wilson Cycle traces the lifespan of an ocean basin through formation, growth, and destruction.

Wilson Cycle Embryonic Stage

Continental uplift pulls the land apart to create rift valleys, as seen in the East Africa rift valleys.

Wilson Cycle Juvenile Stage

Seafloor spreading floods rift valleys to form narrow seas with matching coastlines, as seen in the Red Sea.

Wilson Cycle Mature Stage

Continued ocean divergence expands the sea into a wide basin bounded by continental margins, like the Atlantic Ocean.

Wilson Cycle Declining Stage

Subduction around basin edges shrinks the ocean and creates island arcs and trenches, as seen in the Pacific Ocean.

Wilson Cycle Terminal Stage

Convergence narrows the ocean basin into shallow seas bounded by uplifting mountains, like the Mediterranean Sea.

Wilson Cycle Suturing Stage

Complete ocean closure causes continental collision and uplifts massive mountain ranges, such as the Himalayas.

Continental Drift Hypothesis Criticisms

Alfred Wegener's hypothesis was dismissed primarily because it lacked a working physical mechanism.

Deepest Hole Drilled

The Kola Well in Russia, reaching $12.2\,\text{km}$ deep.

Seafloor Spreading Theory

Proposed by Harry Hess and Robert Dietz as the driving mechanism for plate tectonics.

Ocean Floor Magnetic Anomalies

Rocks record Earth's magnetic polarity changes as hot lava cools at ridges.

Richter Scale

A logarithmic scale measuring earthquake magnitude and frequency.