Plate tectonics

additional notes/resources/practice:

Earth's Interior & Tectonic Plates 2025.pptx

Plate Tectonics (evidence, magnetic reversal)

Plate Boundaries (convergent/divergent/transform)

Hot Spots and Oceanic Features

Plate Boundaries Cheat Sheet!!!

Topics:

Crowe said if its drawing problem it could be like draw a subduction zone and explain or draw hawaii hot spot and explain

Density:

helps explain a lot of ts

how much stuff is packed into one place

Warmer → more spread apart → less dense → rise

Colder → more packed together → more dense → sink

Layers of the Earth:

Has layers and gets structure due to different layers of density

compositional - based on material makeup

crust

made of oxygen + silicone

where we live

Continental

Oceanic

Thick (10-70 km)

Buoyant

Older

Sedimentary + Metamorphic rock

Thin (~7 km)

More dense (sinks under continental)

Younger

Igneous rock

mantle

intermediate composition

mostly iron, magnesium, aluminum, silicon, oxygen silicate compounds

like your fingernails solid but can deform

Convection in this region drives plate tectonics

Depth of 10 km-2890 km

+1000 degrees C

core

mostly iron + nickel = very dense

mechanical - based on physical behavior

Lithosphere

crust + upper mantle

rigid lithosphere creates tectonic plates

Outer, solid part of the earth

100 km thick

rigid rock = cannot bend or flow

asthenosphere

plastic rock = flow due to deformation

still solid rock

mesosphere

outer core

molten liquid

About 3700 degree C

2980-1500 km

inner core

solid + unattached to mantle

suspended in molten outer core

5150-6370 km (3219-3981)

4% of the core by volume

~6000 degrees c

Continental drift

Proposed by German Scientist Alfred Wegner (a meteorologist)

hypothesis that crust moved

couldn't explain how

theory of supercontinent pangea (broke apart 200 million years ago)

Evidence

Continental shapes

seem to fit like a puzzle

supercontinents have been formed multiple times in history

Fossils

Same fossils of same age but on different continents

How did they get there without crossing oceans???

Mesosaurus: freshwater reptile

Glossopteris: plant

Rocks and Mountain Ranges

matching on different continents

rocks in florida match rocks in africa

appalachian mtn match caledonian mtn

Climatic Clues

glaciers in warm places

Must have been connected at higher latitudes

coal on antarctica

coal is made of plant + animal remains

must have been located closer to equator

Seafloor Spreading

Harry Hess (geologist) studied Mid-Ocean ridges

ocean floor is young at ridges

magma comes up + spread then sink back down through ocean trenches = seafloor spreading

ocean floor is like a conveyor belt

Hess’ ideas helped prove Wegner’s

Evidence 1 = Age

plates pull apart → magma erupts → cools + solidifies → new crust → new crust pushed away to form more new crust →old crust recycled back into the mantle → youngest crust at ridge

Evidence 2 = Magnetic Reversal

magnetic North and South pole

normal polarity when compasses point north/ when north is magnetic pole

reverse polarity is when south becomes north

Geographically never change just the magnetic poles

Reversal is recorded in seafloor rock

Molten material rises → iron particles line up with magnetic field since its highly magnetic → stay in place after hardening like stripes

we know this b/c US Navy mapped ocean floor in WWII with a magnetometer

new oceanic crust (basalt) is being made at all times + rocks a perfect record of magnetic reversal

“striped” pattern of alternating magnetic orientation on both sides of the mid-ocean ridge.

symmetrical mirror-image pattern on both sides the mid-ocean ridge = HELPED PROVE SEAFLOOR SPREADING

Atlantic ocean is currently widening today

Plate tectonics

crust divided into 12 plates

plate motion causes collision, separating , or scraping of the plates → tectonic features

Tectonic→ deformation of the crust bc of plate interaction.

drivers of plate motion

lithospheric plates are moved by hot mantle convection causing the lithosphere to slide over the asthenosphere

material in the mantle rises towards lithosphere → cools + sinks down to the mantle

slow + incessant process

plate boundaries

Evidence

divergent

Force = tension

Process: Two plates move apart → hot molten material rises → volcanic activity

Where: Continents + ocean floor

What: Ocean ridges

Example: Iceland

formed as north american + eurasian boundaries diverged

Convergent

force= compressional

Occurs when two plates move towards each other

Styles:

Continental continental

Process: Same properties = neither can sink under →Keep pushing against each other → crust buckles + cracks

What: mountain ranges

Example: European Alps + Himalayas

Continental oceanic

Process: different properties = oceanic can sink under continental → subduction → oceanic heats + dehydrates

What: volcanism

Example: Andes Mountains/Volcanic Belt

Oceanic oceanic

Process: collide → one runs over the other → subduction zone → subducting plate is bent down in a very deep depression

What: trench

Process: as subducting plate melts → hot material rises through crust → volcano series

What: island arcs

Causes: tsunamis + earthquakes

Ring of Fire

Formed around the pacific plate (border of pacific ocean)

Lots of volcanic and earthquake activity, and lots of trenches

Convergent boundary (pacific plate is being subducted)

transform

Force: shear

Process: plates slide past each other → lithosphere is neither created nor destroyed

What: Fault lines

Where: ocean floor connecting ridges

Causes: earthquakes

crust gets stuck and then slips abruptly

Example: San Andreas fault

Special bc transform + strike slip fault

Strike slip fault is when two blocks slide past each other doesnt have to be at a plate boundary

hot spots + mantle plumes

Hotspot volcanoes: hot mantle plumes breaching the surface in the middle of a tectonic plate (NOT AT PLATE BOUNDARIES)

Hotspot: fixed point where magma flows through crust (DOES NOT MOVE)

Tectonic plates move over hot spots forming a chain of volcanoes

Gets older the further away you move

Ex. Hawaii (oldest Kauai)

Ex. Yellowstone

supervolcano

You are in the caldera of it when you visit

Ocean Features

*TOPOGRAPHY: elevation of land ABOVE sea level*

**BATHYMETRY: depth of landforms BELOW sea level**

Continental Shelf

The extended perimeter of each continent

Part of the continent during glacial periods, but in interglacial periods its underwater

Continental slope

The descending slope that connects seafloor to the shelf (considered part of continent)

Continental rise

A gentle slope with a smooth surface

Made by buildup of sediments from erosion

Between slope and abyssal plain

Abyssal plains

Flat or gently sloping areas

Typically considered ocean floor

Found between continental rise and mid-oceanic ridge

Mid-Ocean ridges

Underwater mountain range with rift in the middle

Formed by plate tectonics

Ocean spreading center and is responsible for seafloor spreading

Volcanic fissure

linear vent → lava erupts

along rift zones

Hydrothermal vent

Fissure on seafloor → geothermal heated water discharges

found near volcanically active places

Trench

Long but narrow topographic depression on the ocean floor

Formed at subduction zones

Ex. mariana trench deepest part of ocean

Submarine canyon

Narrow deep canyon carved into continental shelf by erosion

Sea Mount

Mountain rising from the ocean floor that does not reach surface

Formed from extinct volcanoes

Not an island bc it does not reach surface

Guyot

Flat topped seamount

Aka tablemount

Flat bc of erosion by waves, winds, and atmospheric processes

Oceanic island

Found in volcanic island arc

Arise from volcanoes due to subduction

Coral Reef

In tropical shallow water they can form off top of volcanoes

Fringing : close to shore on mainland or cost

Barrier: water separating the shore from the reef, creates lagoon

Atoll: island of coral that surrounds a lagoon, og island is gone

Mid-Ocean Ridges, Trenches, seaounts, and guyots are all created by plate tectonics