Chapter 2: Plate Tectonics Overview

Plate Tectonics Theory

The theory that the outer layer of the Earth (The lithosphere) is broken in several plates that move relative to one another.

Continental Drift hypothesis

Earth's Continents were originally connected, and then drifted apart to their present position.

Evidence for Continental Drift

Coast lines of some continents fit together like pieces of a jigsaw puzzle; matching rock formations, mountains, fossils, and glacial formations across oceans; evidence of glaciers on continents that are currently around the equator & tropical fossils found on land that is currently located in Polar-Subpolar regions.

Proposer of Continental Drift hypothesis

Wegener; rejected due to lack of a viable explanation for the mechanism of continental movement.

Magnetic stripes on the seafloor

Equipment to measure magnetic fields on the ocean seafloor was developed to aid in submarine navigation and represent the changes in the direction of the Magnetic Pole.

Role of Earth's outer core in magnetic patterns

Magnetic patterns were caused by Earth's magnetic Field flipping back & forth, reversing its polarity.

Discovery of magnetic stripes

Provided physical proof of seafloor spreading, mechanism for plate movement, and confirmation of Earth's dynamic crustal changes.

Evidence for seafloor spreading

Magnetic Stripes on the Ocean Floor, Age of Oceanic Crust, and Seafloor Features & Heat Flow.

Volcanism and earthquakes relation to plate boundaries

Reflects large-scale Earth Processes; tectonic activity.

Divergent plate boundary

A type of plate boundary where two tectonic plates move away from each other.

Convergent plate boundary

A type of plate boundary where two tectonic plates move towards each other.

Transform plate boundary

A type of plate boundary where two tectonic plates slide past each other.

Divergent

Oceanic lithospheric plates move away from each other - widening of oceans (New oceanic crust forms)

Convergent

Lithospheric plates move toward each other & crust is deformed or destroyed (Subduction/Continental Collision)

Transform

Plates slide sideways/horizontally past each other in different directions - shearing motion

Relative Plate Motion

Divergent - Away, Convergent - Towards, Transform - Slides Past

Convergent Features

Mountains, Volcanoes, Ocean Trenches, and Accretionary Prism

Divergent Features

Rift Valley and Mid-Ocean Ridges

Transform Features

Fault Lines and Earthquakes

Magma Formation by Subduction

As it goes deeper, it gets hotter and the pressure increases. The water and other stuff from the sinking plate help to melt the rock in the mantle above it. Subduction helps melt the mantle rock, creating magma that rises up and can cause volcanic activity.

Magma Formation by Divergent Boundaries

The space between the plates allows the pressure on the mantle below to decrease. When the pressure drops, the mantle rock melts and turns into magma.

Subduction in Plate Tectonics

When the denser plate is pushed beneath the more buoyant plate & into the mantle

Wilson Cycle

The ongoing cyclical process of the origin & breakup of supercontinents

Mechanisms of Plate Tectonics

Mantle Convection, Ridge Push, and Slab Pull

Tectonic Plate Movement Scale

A Cm per year

Evidence for Plate Movement

Global Positioning System Measurements, Hotspot Volcanic Chains, and Magnetic Stripes on the Ocean Floor

Hot Spots

An area where magma breaks the crust & creates a volcanic center or islands in the ocean, and mountains and calderas on land, not associated with plate boundary

Formation of Hot Spots

A plate moves over a rising 'stable' mantle Plume (hotspot)

Hot Spots and Plate Tectonics

Southwest movement of North Amer. Plate indicated by increase in volcanic center age to the southwest

Volcanic Island Arcs

Formed by subduction at convergent boundary, shaped as a curved arc, with subduction, earthquakes, and volcanoes as tectonic activity, examples include Japan and Aleutian Islands.

Volcanic Island Chains

Formed by hot spot under moving plate, shaped as a linear chain, with hot spot volcanism and minimal tectonic activity, examples include Hawaii and Galapagos.