GEO Week 2 - Plate Tectonics

What are the main layers of the Earth

Crust → Mantle → Core

What is the crust

Earth’s outmost layer; thin, cool, and solid (what we stand on and see)

What is the mantle

Layer beneath the crust; thicker, hotter, and solid to semi-solid

What is the lithosphere

The crust plus the uppermost mantle; rigid outer shell of the earth

• bends/dips when weight is placed upon it

• floats/sits atop the asthenosphere

What is the asthenosphere

Wam, soft layer of mantle beneath the lithosphere. Flows slowly and once cooled becomes magma

What are the two types of lithospheres

Continental lithosphere and oceanic lithosphere (also, for tectonic plates)

Continental lithosphere

Thicker (150 km)

crust is made up of felsic and intermediate rocks. (rich in silica → lower density)

mantle is made up of iron (low in silica → high density)

Oceanic lithosphere

Thinner

The crust is made up of mafic rocks, low in silica → high density

Denser so it subdues or “sinks”

What is a plate boundary and the 3 different types of plate boundaries?

The zone where two tectonic plates interact

Divergent, Convergent, and Transform

Divergent Boundary

Plates move apart from each other

Convergent boundary

Plates move toward each other

Transform boundary

Plates slide past one another horizontally (going different ways)

What forms at divergent (<>) oceanic boundaries?

Mid-ocean ridges and new oceanic lithosphere

How is a new seafloor created

Asthenosphere rises, cools into magma and fills the gap space, eventually the magma solidifies at the ridge axis creating a new sea floor

What process causes melting beneath mid-ocean ridges

Decompression melting

What is a magma chamber

Reservoir of magma beneath the ridge

What rock forms when magma solidifies underground

Gabbro

what rock forms from magma that reaches shallow sheevels of the seafloor

basalt

what is subduction

the sinking of one tectonic plate beneath another in the mantle

what plate usually subducts: oceanic or contiential?

oceanic bc its more dense

continental doesn’t subduct because its too buoyant (less dense)

what happens when continental crust reaches subduction zone?

Subduction may stop (because continental crust is less dense = no subduction), leading to a collision between plates

What is the Wadati-Benioff Zone

band of earthwuales that outlines a subducting plate

what is an ocean trench

deep depression where a plate bends and begins subduction

what is an accretionary prism

sediment scraped off the subducting plate and added to the overriding plate

this happens in convergent boundaries (subduction zones)

what is a volcanic arc

chain of volcanoes formed above a subduction zone

what is a continental volcanic arc

volcanic arc formed on continental crust

what is a volcanic island arc

a volcanic arc formed on ocean crust

what is a back-arc basin

small ocean basin that forms behind a volcanic arc (depre from explosions and subduction zones)

what is a fracture zone

long break in the seafloor that offsets ridge segments

what is a transform fault

actively moving portion of a fracture zone (this is the earthquake part)

what is continental rifting

streching and splitting of a continent

what happens to lithosphere during rifting

stretches horizontally and thins vertically

what can form if rifting continues

a new ocean basin and mid-ocean ridge (aka convergent → new seafloor)

what is a continental collision

convergence of two buoyant (less dense) continental plates

causes large mountain ranges (Alps and Himalayas) because crust thickness and uplifts

what is ridge push

gravity pushes lithosphere away from the elevated mid-ocean ridge

what is slab pull

the sinking subducting plate pulls the res to the plate along —> dragging another plate w it

what process destroys oceanic lithosphere

subduction at convergent boundaries

what boundary creates crust?

divergent boundary

what boundary destroys crust

convergent boundary

what boundary neither creates nor destroy crust; instead cause earthquakes and tsunamis

transform boundary