lecture 3 + 4 ~ plate tectonics

what is the structure of the earth?

1 - crust (thinest layer, made of solid rock)

2 - mantle (thickest layer, made of flowing sold/molten material)

3 - outer core (molten material)

4 - inner core (solid)

what is the crust made of?

light elements (oxygen + silicon)

what are the properties of the continental crust?

thicker

silica rich

less dense (granitic)

varies in thickness due to crustal stretching

what are the properties of the oceanic crust?

thinner

silica poor

more dense (basaltic)

remains roughly same thickness

what are the properties of the mantle?

largest ;ayer

source of all crustal material (magma)

rich in heavy elements (Fe + Mg)

has movement caused by convection currents

what is the lithosphere?

upper most part of the mantle

rigid and cold

what is the asthenosphere?

part of mantle below lithosphere

flows and moves in plastic manner

what are the properties of the outer core?

molten

composed of Fe + Si

has magnetic field

what are the properties of the inner core?

solid

metallic core (Fe + Ni)

what is catastrophism?

belief that earth was young and shaped by violent events

what did james hutton propose?

theory of uniformitarianism (geological events can be explained by natural forces occurring today)

what did alfred wegener propose?

proposed that continents drifted slowly over the globe and were once pangea

what was the issue with wegeners theory?

there was no known mechanism that allowed the continents to move

what evidence is there for pangea and continental drift?

continent shorelines seemed to fit together

matching ancient rock units

similar fossils in diff continents

evidence of glaciation

coal deposits (formed in warm areas) found in cold areas

what did harry hess do?

used echo sounding to map seafloor

what are MORs?

submerged mountain regions with central rift valley

how does the magnetic field support the evidence that the seafloor is spreading?

magnetic minerals preserve polarity when they solidify

MORs have the same pattern of magnetic stripes on both sides

how does sediment thickness change with respect to MORs?

closer - less/no sediment, younger

farther - thicker, older sediment

what are deep ocean trenches?

where crust is being destroyed

what is the sea floor spreading hypothesis?

1 - oceanic crust os created ad MORs

2 - oceanic crust spreads laterally

3 - ocean crust goes back into the mantle at DOTs

what are plates?

regions of thin rigid slabs of crust encircled by seismic belts

glide over soft semi-molten zone in asthenosphere

what are seismic belts?

plate boundaries

what is the theory of plate tectonics?

earth is divided into rigid plates which are in constant motion

what are the types of plate boundaries?

divergent boundaries

what happens at divergent boundaries?

plates move away from each other

crust is created

have active volcanos at site

eg. MORs

what happens to the mantle as it gets farther from the MOR?

it becomes colder and denser losing buoyancy and pulls the plate down

what is rifting?

when continental lithosphere stretches and breaks apart

magma is created

if rift splits continent, MOR is formed

what happens at convergent boundaries?

plates collide and crust is recycled

can be O-O, O-C, C-C

what happens at ocean-ocean collision zones?

older plate subducts since it is colder + denser

creates deep sea trench

how do ocean-ocean collisions cause volcanos + earthquakes?

as plate subducts, it heats up and releases volatiles which melts other plate creating volcanos, earthquakes + magma

which plate do volcanos form on in collision zones?

the plate that is NOT subducting

what happens at ocean-continent collisions?

oceanic plate always subducts since it is older and heavier

volcanoes are formed on continental crust

what happens at continent-continent collisions?

neither crust subducts and instead goes up and forms mountain ranges with thick crust

no volcanos

how do continent-continent collisions occur?

oceanic plate collides with continent and subducts pulling other continent along with it

what occurs at transform boundaries?

plates slide by eachother

occurs at ridge segments

creates earthquakes

what are hotspot volcanos?

isolated volcanos not associated with plate boundary

lay above mantle plumes

what are the types of hotspots?

oceanic crust hotspot - form basaltic island chains

continental crust hotspot - form rhyolitic volcano

how do hotspots and mantle plumes show evidence of plates moving?

plates move OVER hotspots therefore they can show which direction the plates moved because of extinct volcanos