Earth Science Tectonics

Continental Crust

Rich in non-ferromagnesian silicates (felsic) and has a thickness of 40-70km.

Oceanic Crust

Rich in ferromagnesian silicates (mafic) has a thickness of 0 - 8km.

Mantle

Consists of Ferro-Magnesian Silicates (Ultra-Mafic).

Mohorovičić Discontinuity

A chemical composition boundary between the mafic or felsic crust and the ultramafic (upper) mantle; it is the 1st mantle layer.

Lithosphere

1st layer in the mantle, Includes the crust and uppermost mantle; it is rigid and brittle.

What is the second layer of the mantle called?

Asthenosphere

What qualities of layer is there in the asthenosphere?

Hotter and weaker layer in the upper mantle

What is the state of matter of the asthenosphere?

Solid (<3% liquid) but behaves like a fluid over long geologic time periods

What is the characteristic of the asthenosphere?

Partly melted and ductile

What does the asthenosphere permit?

It permits the overlying lithosphere to mechanically detach from the layer below

What is the third lower sphere of the Earth's atmosphere called?

Mesosphere

What counteracts the weakening effects of high temperatures in the mesosphere?

Increased pressure

How do rocks behave with depth in the mesosphere

Rocks strengthen with depth

What type of flow is possible in the mesosphere?

Plastic flow

What are the characteristics of rock in the mesosphere?

Solid and Ductile

Core

Composed primarily of iron (Fe) and a lesser amount of nickel (Ni), with oxygen and sulphur mostly in the liquid outer core.

Theory of Plate Tectonics

Movement of lithospheric plates that shift continents and causes volcanism, earthquakes, and mountain building.

Divergent plate boundaries

Plates spreading apart.

Transform plate boundaries

Occurs between two offset segments of a mid-ocean ridge (seafloor spreading centres); causes earthquakes but no volcanoes.

Plates rubbing against one another, forward and back

Convergent plate boundaries

Plates pushing together, one above the other (subduction or collision zones).

Oceanic plate

Divergent plate boundary within oceanic crust.

Continental Plate

Divergent plate boundary within continental crust; will eventually form oceanic crust.

Continental rift zone

Elongated depression generated when continental crust is pulled apart.

Step 1 of tectonic plate movement

Hot, less dense, buoyant magma forms at the outer core-mantle boundary and rises to the base of the lithosphere where it cools.

Step 2 of tectonic plate movement

Pushing apart plates as new rock forms.

Step 3 of tectonic plate movement

The process where the cool, dense crust subducts and sinks into the mantle as the process repeats again

Trench

Deep valley on the ocean floor, created by the subduction of oceanic lithosphere.

Accretionary prism/wedge

Wedge of sediment accumulated onto the continental plate as the oceanic plate subducts.

Orogeny

A process in which a section of the earth's crust is folded and deformed by lateral compression to form a mountain range.

Oceanic-continental convergent plates

Forms a trench and accretionary wedge with abundant volcanism and earthquakes.

Oceanic-Oceanic convergent plates

Older oceanic plate subducts since it is colder and denser.

Continental-Continental convergent plates

Creates very thick continental plate, large mountain belts (e.g., Himalayas), abundant earthquakes with rare volcanism.

Transform plate boundaries

Fault lines that cause earthquakes but not volcanism, occurs in oceanic-oceanic, continental-continental and oceanic-continental convergent plates.

Paleomagnetism

Magnetic field of the earth recorded in rocks, helps understand sea floor spreading.

Sea floor spreading

Occurs at mid oceanic ridges, where tectonic plates diverge due to magma rising from the mantle which solidifies and forms new oceanic crust.

Mantle plume

Column of plastic upwelling of magma within the mantle which creates volcano.

Hotspot

Magma generated by this rises through the lithosphere and produces active volcanoes at the Earth's surface.

Continental shelf

Submerged edge of a continent which slopes at 0.1 degrees and features several km thick accumulation of water sediment.

Continental Slope

Steep sloping descent which marks the boundary between the continental and oceanic crust.

Abyssal Plain

The nearly flat plain on the deep ocean floor.

What is an active continental margin?

A continental margin that has a convergent plate boundary, thin continental shelf, volcanism, earthquakes, deep trench offshore

What is a passive continental margin?

A continental margin that has no plate boundary, thick continental shelf, thick sediment accumulation, no trench, no earthquakes, no volcanoes

Theory of continental drift

The hypothesis that continents have moved over geologic time, resulting in their current positions, proposed by Alfred Wegener.

average ocean depth

4,000 metres