Earth Structure and Characteristics

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Learning Goal 1

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Earth’s Layers

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Earth Structure and Characteristics

Earth Materials and The Cycle Of Rock Change

Sediments and Sedimentary Rocks

The Cycle Of Rock Change

Relief Features Of The Ocean Basins

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.

Ocean basins are contained in The crust. opic

Earth continents and ocean basins were created by the continuous movements of Lithospheric plates in geologic timescales on the surface of the Earth

Arc-Continent Collision

Configuration Of The Continent

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

Arc-Continent Collison

Continuation of collision leads to formation of new subduction boundary

Another oceanic fracture develops.

Resulting mass of rocks is called an orogen

Formed through the process of orogeny

Layers of sediment on continental shelf and slope are affected

Thrust far inland over older continental rocks

Crushed and deformed

Island arc collides with passive continental margin

Not subducted, but pushed up against the continent

Island arc is thick and buoyant

Continent-Continent Collison

Ancient sutures marking early collision

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

Appalachian Mountains (Eastern North America)

Ural Mountains (Europe-Asia)

Collision zone is called a continental suture

The collision unites two plates

Resulted by the ongoing closing of ocean basin

The Wilson Cycle and Supercontinents

Supercontinent Cycle

Dispersal

Supercontinent Formation

Convergence

The Wilson Cycle

Stage 6 —The Form Of Continental Suture

Stage 5 — Closing Continents

Stage 4B — The Rising Of Island Arcs

Stage 4A — The Closing Of The Ocean Basin

Stage 3 — Old Ocean Basin

Stage 2 — Young Ocean Basin

Stage 1 — Embryonic Ocean Basin

Island Arcs and Collision of Oceanic Lithospheric Plates

Example: Aleutian Islands

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

Fracture produces a subduction boundary

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

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

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

Subducted oceanic crust is altered due to water reaction

Subduction occurs when fracture happens at a passive continental margin

Continent ruptures to form an ocean basin with axial rift

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

Two plates move apart and create a new ocean

Igneous Rocks

Metamorphic Rocks

Types of Metamorphic Rocks

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

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

Definition of Metamorphosis

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

Formation

Subtopic

Relief Features Of The Continents

Plate Tectonics

Continental Rupture and New Ocean Basins

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

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

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

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

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

Definition: Continental lithosphere fractures and splits apart

The Power Source for Plate Movements

Radiogenic heating

The Descending Theory

Gravity Gliding Theory

Convection Currents Theory

Continental Rupture and New Ocean Basins

The Crust and Lithosphere

Lithospheric plates

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

large pieces of lithospheric shell that can move independently

Lithosphere

ranges in thickness from 60 to 150 km

including crust and cooler upper part of mantle

brittle rock

outer Earth shell of rigid

Continental crust

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

Oceanic crust

consists almost entirely of mafic rocks

Contains continents and ocean basins

7-40 km thick

Composed of varied rocks and minerals

Separated from mantle by Moho discontinuity

Thin, outermost layer of Earth

The Mantle

Upper Mantle

molten material forms in hotspots

softer and plastic (asthenosphere)

lower temperature and pressure

Lower Mantle

hotter but largely rigid due to intense pressure

Subdivided into zones with different temperatures and compositions

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

Temperatures range from 1800°C to 2800°C

Mafic silicate minerals

The Core

Inner Core

extreme pressure keeps it solid despite high temperatures

solid iron

Outer Core

generates a magnetic field

liquid iron