Earth Structure and Characteristics

Outer Core

liquid iron

generates a magnetic field

Inner Core

solid iron

extreme pressure keeps it solid despite high temperatures

Mafic silicate minerals

Temperatures range from 1800°C to 2800°C

Largest layer, makes up over 80% of Earth's volume

Subdivided into zones with different temperatures and compositions

Lower Mantle

hotter but largely rigid due to intense pressure

Upper Mantle

lower temperature and pressure

softer and plastic (asthenosphere)

molten material forms in hotspots

Thin, outermost layer of Earth

Separated from mantle by Moho discontinuity

Composed of varied rocks and minerals

7-40 km thick

Contains continents and ocean basins

Oceanic crust

consists almost entirely of mafic rocks

Continental crust

consists of lower zone of dense mafic rock and upper zone of lighter felsic rock

Lithosphere

outer Earth shell of rigid

brittle rock

including crust and cooler upper part of mantle

ranges in thickness from 60 to 150 km

Lithospheric plates

large pieces of lithospheric shell that can move independently

can separate or collide to create relief features like continents and ocean basins

Radiogenic heating

Convection Currents Theory

Gravity Gliding Theory

The Descending Theory

Definition: Continental lithosphere fractures and splits apart

Causes: Tectonic forces uplift a plate of continental lithosphere and pull it apart

Result: Formation of a wide ocean with an axial rift and passive continental margins on either side

Passive continental margins: Where continental lithosphere is joined to oceanic lithosphere with no motion between them

Example: Red Sea - triple junction of three spreading boundaries established by the motion of the Arabian plate pulling away from the African plate

Formation process: Initial formation of a rift valley leads to the sinking of the bottom below sea level and allows seawater to enter

Formation

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Definition of Metamorphosis

Metamorphism is a process that changes preexisting rocks into new forms because of increases in temperature, pressure, and chemically active fluids.

Types of Metamorphic Rocks

Foliated: they have formed in an environment with either directed pressure or shear stress.

Not Foilated: they have formed in an environment without directed pressure or relatively near the surface with very little pressure.

Continent ruptures to form an ocean basin with axial rift

Two plates move apart and create a new ocean

Plate motions may reverse and the ocean basin may start to close

Fracture produces a subduction boundary

Subduction occurs when fracture happens at a passive continental margin

Subducted oceanic lithosphere plunges downward, and oceanic crust is carried into the mantle

Subducted oceanic crust is altered due to water reaction

Melted altered crust forms magma that rises and erupts on the seafloor

Island arc is formed by new volcanoes that grow and fortify from below

Accretionary wedge of sediments forms from piled-up seafloor sediment in the trench

Example: Aleutian Islands

The Wilson Cycle

Stage 1 — Embryonic Ocean Basin

Stage 2 — Young Ocean Basin

Stage 3 — Old Ocean Basin

Stage 4A — The Closing Of The Ocean Basin

Stage 4B — The Rising Of Island Arcs

Stage 5 — Closing Continents

Stage 6 —The Form Of Continental Suture

Supercontinent Cycle

Convergence

Supercontinent Formation

Dispersal

Resulted by the ongoing closing of ocean basin

The collision unites two plates

Collision zone is called a continental suture

Ancient sutures marking early collision

Ural Mountains (Europe-Asia)

Appalachian Mountains (Eastern North America)

Caledonian Mountains (Scotland, Norway, Svalbord, Eastern Greenland)

Island arc collides with passive continental margin

Island arc is thick and buoyant

Not subducted, but pushed up against the continent

Layers of sediment on continental shelf and slope are affected

Crushed and deformed

Thrust far inland over older continental rocks

Resulting mass of rocks is called an orogen

Formed through the process of orogeny

Continuation of collision leads to formation of new subduction boundary

Another oceanic fracture develops.

Earth surface features formed are driven by the lithospheric plates’ movement that slides over the hot viscous asthenosphere.

Configuration of our continents must have changed many times over the history of the earth

Ocean basins are contained in The crust.
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Earth continents and ocean basins were created by the continuous movements of Lithospheric plates in geologic timescales on the surface of the Earth

Ocean basins include a midoceaning ridge with a central axial rift where crust is being pulled apart

The margins of the Pacific Ocean Basin have deep offshore oceanic trenches

In the North Atlantic Ocean, two large tectonic plates are spreading apart and moving away from a central rift.