Plate Tectonics Flashcards
Magnetic striping
Patterns of magnetism preserved in rock on each side of ocean ridge
Continental drift
Separating of continents by drifting across the oceans
Plate Tectonics
Theory that earth’s crust is cracked into many large pieces ( tectonic plates) that move on asthenosphere
Rifting
Process of continents breaking up, subsiding and allowing in the sea
Seafloor spreading
Process of new crust forming at ocean ridges & spreading outwards
Island arc
Chain of Islands formed at edges oceanic and oceanic plate boundaries where one subducts
Earthquake
Rapid movement of ground, usually up & down & back & forth in a wave motion
Seismic wave
The shaking, wave like movement that travels though Earth
Surface wave
Seismic wave travels along surface of Earth in crust
Observations that led to hypothesis of sea floor spreading
Discovery of the global rift system (cracks in middle of ridges) and ocean ridges
Subduction
Crust sinking under another plate = trenches, volcanic arc (on land) Island arc (chain of Islands)
Evidence of continental drift
Jigsaw puzzle, fossils of same species found on continents far apart, glacial sediments in places where don’t exist now, glacial scratches line up
How Wegener deduced what Pangaea looked like?
Rearranged continents- join, fit like puzzle & distribution of fossils was continuous across land masses
Hess’s theory of Seafloor spreading
Proposed new crust formed at ocean ridges & spreading outwards - crust sinking down into earth in ocean trenches = subduction
3 types of evidence that supports sea floor spreading
Magnetic striping- rocks at particular distance on both sides of mid ocean ridge had same magnetic direction
Older rocks further away from ridges
Sedimentary layers thicker as move away from ridges
Why Africa and America older than Seafloor of Atlantic
New Seafloor constantly created & destroyed while continents remain at surface, moving around on the plates
Explain process of magnetic striping
Coloured areas represent rock formed when mag field was same as today, grey = when reversed
Magnetic minerals in rocks line up in like compass & point north as magma cools.
Layers symmetrical on both sides of axis coz magma separates away on both sides =ly as cooling
How convention & heat involved in movement of plates
Rocks of asthenosphere very hot & viscous. Heat creates convention cells in mantle with warm rock pushed ^ & cooler rock sinking down. As rock ^ & flow sideways beneath crust, plates dragged by friction
Compare theories of CD & PT
Both proposed continents moved
CD - no mechanism or evidence
Plate tectonics- proposed crust cracked into large pieces called TP, subduction & Seafloor spreading explained movement
Distinguish between mag striping & mag reversal
Mag striping- bands of alternating mag field that symmetrical on both side of ridge
Mag reversal- where mag field reveres & N becomes S - preserved in rocks
How Red Sea formed
Rifting when 2 plates separated, subsides & allowed sea from N & S, flooded Rift Valley
Why geologist believe Aus moving N if there’s ocean trench Aus & indo & ridge between Aus & Antarctica
New crust forms forms S of Aus & pushed plate northwards where it subducts under indo
Evolution of flora & fauna by change in environmental conditions following break up of Gondwana
Aus separated from Antarctica 40 MYO - allowed cold current to cool Antarctica & lock up moisture that fell as rain in Aus. S Aus become drier, drifting ^ , become more arid as it entered tropical region –> flora that was adapted to dry conditions
Indian plate & Eurasian plate collide
Both light crust, same densities, pushed upwards = fold mountains
Fossils found on Mt Everest
Seafloor sedi rocks from Indian plate uplifted
Why Aus became drier
Movement of plates allowed formation of cold current & this locked lots of moisture in Antarctica- reduced rainfall in S Aus. Warm currents formed & temp rose as ^ into topics & rainfall declined
Why quakes and volcanoes mainly found near plate boundaries
Place where earth moves most , expected to have most severe quakes, most E generated for earth movement, volcanoes occur at PB where magma can reach surface through weaknesses by plate movement - subduction generates heat
Damper
Structures that move in opposition to seismic waves & appose their affect
Base isolation
Pads, springs & bearings that allow building to suppress waves by moving rather than vibrating
Island chains
Form over hotspot as plate keeps moving & new volcanoes form one after other. Only one active,
island arc = chain of volcanoes, usually all active
Magma from C & O and from O& O
C plate have more silica in them, makes magma viscous
O & O- rocks with lots of water create steam during subduction, magma not as viscous, lack of silica
Process of Seafloor spreading & subduction & how tees relate to convection
New crust formed at ocean ridges & spreading outwards, eventually results in ocean floor converging with nearby plates & subduction. Both driven by convection currents in mantle
Plate tectonics and discuss it’s past impact on ocean currents and climate on of earth
Ocean currents affected by plate movement eg; Antarctic circumpolar current when Aus separated- cooled Antarctica greatly, formed ice sheets
Warm currents on east of Aus block from getting to Antarctica
Difference in ocean & continental crust
O- dark, dense & low in silica & lighter elements eg: Al
C - light colour, less dense due to high silica content
Compare subduction of O& O and C& O
Both cases one plate subducts, forming trench & volcanic activity occurs
2 O = island arc
C & O = one land, fold mountains
How mountains can form
Collision of C&C, O&C, transform boundaries, diverging boundaries have mountains by volcanic activity, island arcs mountains in sea, hotspots
seismograph, seismometer,
Measures and records details of earthquakes, eg: force & duration
