plate techtonics Flashcards

Question

Features of MAR

Answer 1

7000km- one of largest mountain ranges submarine mafic + ultramafic igneous- from ultramafic lava iceland above sea level- above hotspot central spreading = axial rift valley- median rift formed by extension of crust under tension high heat flow across MOR (peaks at median rift)- thinner + upwell of magma Shallow focus earthquakes- magma pushing through ridgid crust transform faults at 90 to fault- also have shallow focus earthquakes no sediment on MOR (thicker further away + sym) - new no time to deposit oozes + fine sed on ocean floor - dated by pelagic microfossils sediment furthest from MOR 200Ma / Age of crust increases with distance - more time to dep magma accum at shallow magma chambers below fast spreading ridge - move through feeder dykes and erupt as pillow lavas - due to pressure relase + partial melting

Answer 2

New igneous rock forms - basalt, from magma basalt contains iron rich mineral iron rich minerals align with the poles - north whilst still molten basalt solidifies and records poles at time of formation as we move away from MOR we see normal polarity at centre then it alternates reverse/normal symmetrical pattern

Answer 3

reversals - date the igneous rocks (at reversal boundaries) using radiometric dating and assign dates rate of seafloor spreading - date igneous rocks and then measure distance from rocks to MOR distance/time

Answer 4

North- straight down South-straight up equator-parallel

Answer 5

plate is moving rather than the pole but due to the alignment of the rocks it looks as though the pole moved - they used to point at poles but moved so now don't if the wandering curves are symmetrical /match up then it hasn't moved if you look at the wandering curves of diff continents there may be many positions for 1 pole - due to continental drift

Answer 6

2 plates move towards each other (convergence) destructive compressive stress see subduction sometimes - if O plate present (if 2 oldest subducts) see deep focus earthquakes - due to descending plate 3 types- continental, continental continental, oceanic oceanic, oceanic

Answer 7

slower/older/denser plate subducts at trench partial melting of basalt crust as lower temp minerals begin to melt melted minerals=less dense - rise as magma with inter comp (andesite) - some mafic (basalt) as more silica melts first results island arc - sed scraped off descending plate and metamorphosed by increased temp + pressure

Answer 8

Magma rises from subducting O plate is hot enough to partially C crust that it passes through some S magma reach the surface - rhyolitic volcanoes some will mix with rising mafic magma to create large volcanoes of intermediate lavas - build strata volcs of andes ect large batholiths formed from C crust compression of C crust - mountain chains- show regional metamorphism inside due high pressure + temp (gneiss inside to slate outside) may form ophiolite suites

Answer 9

No subduction mountains formed lots of metamorphism in mountains high grade inside - lower grade moving out batholiths

Answer 10

Volc rocks folding - evidence of compression metamorphic rocks + changing grade ophiolites batholiths- silicic magma that doesn't reach the surface

Answer 11

Caledonian orogeny North scot was on Laurentia and the rest was on Gondwana land - collided The lapetus ocean between the 2 continental plates subducted beneath Scotland + north Wales (in Cambrain) formed volcanos, major platonic intrusions, pillow lavas, fossil evidence, large fold mountains - regional met

Answer 12

Movement of Magma through the mantle

Answer 13

Volcanos Above Mantle plumb (away from plate boundaries)

Answer 14

Cabb seasmount Yellowstone Canary islands Amsterdam Island Australia Macdonald seamount Hawaii seamount Easter Island galapagos iceland eifel afar

Answer 15

sesimic tomography- study of the way seismic waves move through earth LVZ- travel slower velocity, travel better in solids so LVZ must be more fluid If the LVZ extend from Guttenberg to the surface - mantle plume above mantle plumb we see Hotspot (volcano) - ultramafic/really mafic erupted material

Answer 16

see active volc that produced youngest island then number of other islands that get progressively older with distance from the Hotspot

Answer 17

mantle plumb remains stationary as the plate moves

Answer 18

Distance from the oldest island to the youngest / time (difference in age)

Answer 19

In the past it was believe plate movement was due to convection currents in mantle only changes in the last 20yrs or so Heat-become less dense-rises-relases heat-contracts-falls now we know they aren't the primary mech for plate movement

Answer 20

Occurs at MOR (divergent) at divergent plate boundaries we get the upward movement of Magma due to pressure release - pushes plate upward and apart pushes up to form MOR as it cools added pressure to 2 plates + new crust formed

Answer 21

Old cold oceanic plate subducts - descends pulling the rest of plate towards subdiction zone may be main cause of plate movement

Answer 22

Ridge push and slab pull

Answer 23

1) breakup of continent at divergent plate boundary- young ridt valley 2) ocean forms and grows with divergence e.g. red sea= young , Atlantic = Older Passive margin cooling 3)subduction begins one oceanic plate meets continental plates which causes subduction Creates volcano chain at active margin e.g.pacific 4)subduction continues continents become very close ocean begins to close e.g. Mediterranean start of convergence + mountain building 5)continents finally collide mountain building orogeny = full Wilson cycle e.g. Himalayas 6)Continent erodes - thinning of crust