Tectonic Boundaries Flashcards
Where does oceanic lithosphere get thinner?
crest of oceanic ridge system
What is denser? Oceanic lithosphere or continental lithosphere?
oceanic
How does the lithosphere respond to forces acting upon it?
bending or breaking
Plates definition
broken down fragments of the lithosphere with irregular size and shape that are in constant motion relative to each other
Difference btw a plate boundary and edge of a continent
plate can include all or part of a continent and part of an ocean basin
Divergent plate boundaries
plates move apart, creating fractures, upwelling of asthenosphere and partial melting of mantle (release of pressure from plates moving apart), magma rises through fractures, solidifies at depth to thicken crust or to create new seafloor
What happens to the lithosphere with transform plate boundaries
no production or destruction, just grinding
What boundaries do eqs happen? volcanic activity?
all
divergent and convergent
What kind of structure does divergent plate boundaries produce?
rift volcanoes
What are deep ocean trenches
what are they offshore of
long linear depression offshore of continent or chain of volcanic islands
what type of plate boundary produces trenches
2/3 types of convergent boundaries (ones with subduction)
Subduction angles and age
old lithosphere is denser and less buoyant so it subducts at vertical angles, young lithosphere is less dense and more buoyant so it subducts at small angles
symbol for divergent plate boundary
rectangle with lines sticking out
OC Convergence
- Oceanic crust is more dense (3.0g/cm^3) than cc (2.7 g/cm^3) so it subducts
- depth of 100km, water crystals in oc triggers partial melting of the asthenosphere
- the molten material (magma) is less dense bc the water lowered the melting temp and pressure
- rises through fractures created when oc pushed and cracked cc
- makes it to surface: continental volcanic arcs
doesn’t make it to surface: thickens crust
Where along boundaries are the trenches located?
oceanic lithosphere descends into mantle along subduction zones
OO Convergence
Oceanic crust that’s more dense subducts
2. depth of 100km, water crystals in oc triggers partial melting of the asthenosphere
3. the molten material (magma) is less dense bc the water lowered the melting temp and pressure
4. rises
5. makes it to surface: volcanic island arcs
EX of OO Convergence
japan
CC Convergence
what causes it?
subduction of seafloor causes two landmasses to move towards each other
1. cc too buoyant to subduct so a collision causes an accumulation of sediments and sedimentary rocks along cont. margins
2. forms mt belts
example of CC convergence
himalaya mts indian plate and eurasia
Accretionary wedge
build up of sediment scraped off an oceanic plate by the overriding plate during subduction.
Symbol for convergent boundary
triangles
Where are transform boundaries found? what do they offset? what do they produce
ocean floor (fracture zones) or continental vs continental (san andres fault)
offset segments of the ridge system, step like plate margin
Where do active transform faults lie? how are they generally defined
btw 2 offset ridge segments
weak, shallow eq (move in opp. directions)
inactive zones
fractures are preserved direction of plate motion at time of formation (move in same direction)
