plate tectonics Flashcards
who gave Evidence supporting continental drift
wegener
who proposed the sea-floor spreading hypothesis
Hess / Dietz
what is plate tectonics a combination of
Sea-floor spreading + continental drift
what 6 things does plate tectonics explain
= Igneous, sedimentary, and metamorphic rocks
= The distribution of earthquakes and volcanoes
= The origin of continents and ocean basins
= The distribution of fossil plants and animals
= The genesis and destruction of mountain chains
= Continental drift
what are tectonic plates made from
fragments of lithosphere (crust & uppermost part of upper mantle) - in motion over the asthenosphere
how does the lithosphere differ from the Asthenosphere when loaded
Lithosphere bends elastically when loaded
Asthenosphere flows plastically when loaded
who first described buoyancy
Archimedes
main concept of buoyancy
Floating solids displace water equal to their mass - this applies to lithospheric plates
2 types of lithosphere and their characteristics
- Continental ~ 150 km thick
Granitic crust
35-40 km thick
Lighter (less dense)
More buoyant – Floats higher - Oceanic ~ 7 to 100 km thick
Basaltic crust
7-10 km thick
Heavier (more dense)
Less buoyant – Sinks lower
3 types of plate boundaries
Divergent – Tectonic plates move apart
Convergent – Tectonic plates move together
Transform – Tectonic plates slide sideways
what is associated with divergent plate boundaries
Mid-Ocean Ridges e.g. Mid-Atlantic Ridge
= Sea-floor spreading causes plates to move apart
= Magma wells up to fill the gap
= Magma cools, adding material to each plate
Pillow basalt – indicated MORs
what can occur at some MORs and how
“Black smokers”
= Water entering fractured rock is heated by magma
= Hot water dissolves minerals and cycles back out of rock
= When water reaches the sea, minerals precipitate quickly
what occurs in Convergent plate boundaries
subduction - one plate goes down into mantle at an average of 45°
- oceanic lithosphere is recycled
- a belt of earthquakes is revealed - Wadati-Benioff zone
3 subduction features
Trench
Accretionary prism
Volcanic arc
explain Accretionary prisms from subduction
Deformed sediment wedges
- Sediments scraped off subducting plates and welded onto the overriding plates
- Can be pushed above sea
explain Volcanic arcs from subduction
Volcanic belt on an overriding plate
- partial melting at ~ 150 km depth -> magmas - volcanic eruptions
- A curved Earth -> Volcanic belts are curved
- 2 Arc types :
= Continental crust – Continental arc.
= Oceanic – Island arc
3 Types of convergent boundaries and their characteristics
- Ocean-ocean – form deep sea trench + volcanic island arc
- Ocean-continent – ocean plate subducts + volcanic belt of mountains formed on continental plate margin
- Continent-continent – crust crumbles + thickens – create high mountains
what are transform plate boundaries characterised by
- Earthquakes
- Absence of volcanism
- Common at mid-ocean ridges
- bear strong evidence of sea-floor spreading
