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1 SOES1008 earth and ocean systems > continental drift paths and plate tectonics > Flashcards

continental drift paths and plate tectonics Flashcards

1
Q

what is the lithosphere?

A

outer 100 km of the earth- an outer shell composed of rock that cannot flow easily. behaves rigidly and doesn’t flow.

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2
Q

what does the lithosphere comprise of?

A

the crust and the upper mantle

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3
Q

what lies below the lithosphere?

A

asthenosphere

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4
Q

what is the asthenosphere?

A

holds upper mantle. shallower under the oceanic lithosphere, deeper under continental. flows like a soft solid. rock can flow in the asthenosphere. made of the entire mantle. roughly up to the point of upper to transition. NOT a liquid.

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5
Q

why are oceanic lithosphere and continental lithosphere different?

A

oceanic has a thickness of 100km. continental topped with crust has 150km.

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6
Q

what did Alfred Wegner find?

A

suggested land lasses slowly move (continental drift), due to plate tectonics.

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7
Q

what was the supercontinent called?

A

Pangaea.

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8
Q

what was Alfred Wegners evidence?

A

the fits of the continents, locations of past glaciations, the distribution of equatorial climatic belts, the distribution of fossils, and the matching geological units.

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9
Q

why did the fits of continents help Alfred Wegner understand continental drift?

A

remarkable few overlaps, they seem to all fit together .this created Pangaea.

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10
Q

why did locations of past glaciations help Alfred Wegner understand continental drift?

A

glaciers form at high altitudes. by looking at past glaciers, you could determine the past locations of the continents. when a glacier moves, it scrapes sediment off the ground. the sediment freezes into the base of the glacier, and so it becomes exposed rock. when the glacier melts, the sediment collected remains on the ground, and creates a distinct layer fo “till”. Wegner found that all the late glaciated areas lie adjacent to each other on the map of Pangaea.

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11
Q

what is till?

A

a mixture of mud, sand, pebbles, and larger rocks

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12
Q

what are some criticisms of Wegeners ideas?

A

no mechanisms, therefore wasnt accepted.

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13
Q

who created the mechanism for the continental drift?

A

Harry Hess, in 1960’s.

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14
Q

what did Harry HEss argue?

A

the continents drift apart because of the new ocean floor forms between them by a process called sea-floor spreading. continents move towards each other when the old seafloor flood between then sinks back down into the earth interior- subduction.

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15
Q

what is the continental “fit”?

A

evidence of Permian glaciers found on 4 continents. fossil evidence, etc. all match geological units. shows that there was once a supercontinent.

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16
Q

what is inclination?

A

curved lines called nagnetic needle. depends on the latitude.

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17
Q

what is polar wandering?

A

the layered layered record magnetic changes over time. inclination and declination indicate changes in position. the pole has been the same, but the continent shave moved and drifted this is evidence for continental drifts. each continent has a separate polar wandering path. the compass represents paleomagnetism.

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18
Q

what is paleopole?

A

refer to the supposed position of the earths magnetic pole at the time in the past. they recorded the magnetic field prserved in rocks from different ages.

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19
Q

how did we find sea flood evidence?

A

WW2 submarines started using echo0sounding (solar), to detect submarines, but also it began rapid sea-floor mapping.

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20
Q

what did the Bathmetric maps reveal?

A

a mid-ocean mountain range runs through every ocean
deep ocean trenches occur near volcano island chains
submarine volcanoes poke up from the ocean floor
huge fracture zones segment the mid-ocean ridge.

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21
Q

how did they find the mapping of the seafloor?

A

scattered “soundings” of the sea floor. the surveyor let out a length of cable with a heavy weight. when it hits the floor, the length of the cable indicates the depth of the floor,,

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22
Q

what are the 2 provinces in the floor?

A

abyssal plains and mid ocean ridges.

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23
Q

what are abyssal plains?

A

broad, relatively falt regions of the ocean tha lie at the depth below sea level

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24
Q

what are mid ocean ridge?

A

crust of the mid ocean ridge “ridge axis”.

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25
Q

what are deep ocean trenches?

A

define elongates troughs that are called trenches. border volcanic arcs, curving chains or active volcanoes.

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26
Q

what are seamount chains?

A

volcanic islands poke up off ocean floor. islands rise above sea level, echo sounding has detected many seamouonts. they occur in chains

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27
Q

what are fracture zones?

A

reveal that the ocean floor is diced up by narrow bands of vertical fractures.

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28
Q

what is the oceanic crust made of?

A

covered with a layer of sediment composed of clay and tiny shells of dead plankton. varies in thickness.

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29
Q

what did Harry Hess find about the thickness of the ocean floor?

A

overall thinness o sediment layers on the ocean floor meant that it is much younger than the continents. the increase in the thickness of sediment away from mid-ocean ridges mean the ridges when young was the deepest parts of the floor. this means that the flood must be forming and getting wider all the time.

30
Q

what is a fault?

A

earthquakes use energy in vibration movements- seismic waves, the break of rock during an earthquake produces a new fracture on which sliding occurs. a fracture which sliding occurs is called a fault.

31
Q

what do magnetometers detect?

A

seafloor spreading, magnetic polarity reversals are imprinted in sea-floor rocks as the sea floor continues to spread. stripes of positive (stronger) and negative (weaker) magnetic intensity.

32
Q

what are reversals?

A

when reversed N magnetic pole is near S geographic pole. reversals are geologically rapid can be used as time markers.

33
Q

what is radiometric dating?

A

define the age of rocks, by measuring the rate of decay of radioactive elements in the rocks.

34
Q

what are chrons and subchrons?

A

magnetic reversal chronology: reversals don’t occur regularly, so the lengths of different polarity chrons- the time interval between reversals. in short intervals, they are sub-chrons.

35
Q

how are marine magneitc anomalies formed?

A

tiny dipoles of magnetic grains in basalt alighn with the earths field. as it forms, the rocks migrate away from the ridge axss. later, when the field has reversed, the light stripes form with reverse polarity. as it forms it also moves away from the axis, and younger crust begins to develop. as this process continues, many lines form.

36
Q

what is deep sea drilling?

A

drill until you reach depths of rock and sediment. the sediment layers should be progressively thicker away from the axis.

37
Q

what are plates?

A

the lithosphere forms the earths rigid shell, but contains a number of breaks, which separate the lithosphere. some of the plate boundarues follow lithosphere into distinct pieces, these are called plates.

38
Q

how many plates are there?

A

12 adn several microplates

39
Q

what are continental margins?

A

some of the plate boundaries follow continental margins, which are the boundaries between a continent and the ocean.

40
Q

how do you distingush active margins?

A

if they follow a continental margin.

41
Q

what are passive margins?

A

crust is thinner than usual.

42
Q

what is the continental shelf?

A

surface of the sediment layer that is shallow and broad. this is the home of fisheries. it is entirely oceanic lithosphere, or entirely continental lithosphere.

43
Q

how much do plates move a year?

A

1-15 cm

44
Q

what happens to the plates as they move?

A

its internal area remains origin and intact, but the rock along the boundaries undergoes deformations as the plate grinds or scapes/ as plates move, so do the continents that form part of the plates- resulting in continental drift.

45
Q

hwo do earthquakes affect the plates?

A

cause shock waves, that are generated when rock breaks and suddenly shears along a fault (a fracture which sliding occurs). the hypocentre of the earthquake is set where the fault began to slip

46
Q

how do the earthquakes define the positioning of the plate?

A

because the fracturing and slipping that occur along the plate boundary as plates move, generate earthquakes.

47
Q

what are the 3 types of plate boundaries that geologists define based on the motion of the plates?

A

divergent
convergent
transform

48
Q

what is a divergent boundary?

A

boundary at which 2 plates ove apart form eachother.

49
Q

what is a convergent boundary?

A

at which 2 plates move towards eachother so that one plate sinks beneath the other

50
Q

what is a transform boundary?

A

at which 21 plate slipes long side another plate sideways.

51
Q

does sea floor spreading create a space?

A

no, hot asthenosphere rises beneath the ridge, and as it rises, it begins to melt. it produces molten rock and magma. the magma has a low density, so it behaves buoyantly and rises.

52
Q

how does the magma form after it rises when sea floor spreading occurs?

A

some solidify alongside the chamber to make coarse grain rock Gabbro. some rise still higher to fill vertical gaps, where it forms sheets of basalt. some magma rises all the way to the surface of the seafloor and spills out of small submarine volcanoes.

53
Q

why are mid-ocean ridges higher?

A

due to the buoyancy of the oceanic lithosphere. as the sea floor ages, the asthenosphere below cools enough to become part of the lithosphere. and the lithosphere mantle thickens.

54
Q

what is buoyancy?

A

refers to the upwards force acting upon an object immercing or floating in a fluid.

55
Q

what is subduction and how is it applied to convergent plates?

A

one oceanic plate bends and sinks down into the asthenosphere beneath another plate. geologists refer to the sinking process as subduction, so convergent boundaries are also known as subduction zones. subduction at a convergent boundary consumes old ocean lithosphere a this closes the oceanic basin. sometimes called trenches.

56
Q

what is the driving mechanisms for plate motion?

A

the convective flow within the asthenosphere does occur, but not directly drives plate motion. hot asthenosphere does rise in some places and sinks in others. ridge push force develops because of id–ocean ridge axis. gravity causes the elevated lithosphere at the ridge axis to push on the lithosphere, making it move away.

57
Q

how fast do the plates move?

A

2 different frames of reference- relative plate velocity distance/time. but if we describe the movement of both plates relative to a fixed point in the mantle, that is absolute plate velocity.

58
Q

what is accretionary prism?

A

subduction feature, as downgoing plates slide under the overriding plate, sediment settled on the surface of the downgoing plate, as well as sand, and gets scraped and incorporated into a wedge-shaped mass known as accretionary prism.

59
Q

what is a triple junction?

A

point at which 3 plates intersect.

60
Q

what are fracture zones?

A

the spreading axis of the mid-ocean ridge consists of short segments. the end of the segments is linked to each other by narrow belts- known as fracture zones. they lie at right angles to ridge segments.

61
Q

what is a transform fault?

A

actively slipping segmnet of a fracture zone between 2 ridge segments.

62
Q

what would happen if there were no earth tectonics?

A

the earth woudl be flat. there would be no moutnaisn, river systems, deltas etc.

63
Q

what are hot spots?

A

most hot spots is located in the interior of plates, away from boundaries. 100 volcanoes exist at isolated points and arent consequence of movement at plate boundaries.

64
Q

where are small volcanoes?

A

lie along mid-ocean ridge

65
Q

what did wilson suggest about hot spot volcanoes?

A

that they develop over a heat source in the mantle that is fixed relative to a moving plate. the active volcano represents the location of the heat source. this is due to there being a chain of dead volcanoes

66
Q

what do the dead volcanoes on hot spots show?

A

the cahin of inactive or seamount volcanoes represent location son the plate that were once over the source.

67
Q

what are mantle plumes?

A

come from the core mantle boundary, where heat form the earths core warms the base of the mantle. as it exapdns, the hot rock above the core mantle becomes less dense and begins to stream upwards. when it reaches the lithosphere, it erupts as a volcano. this is a hot spot.

68
Q

when does the hot spot go extinct?

A

when the plate at which the volcano grows, it continues to shift, so eventually the volcano moves off the pump and dies. meanwhile, a new volcano erupts when over the plume.

69
Q

what is rifting?

A

because of plate motion, oceanic plates form and are later consumed, while continents merge and later split apart. most divergent boundaries form when a continent splits and separates into 2 continents. this is called continental rifting.

70
Q

what happens when two plates collide?

A

subduction comsumes oceans- such as with Asia and India. when India collided with Asia, the attached oceanic plate broke off and sank sown into deep mantle. India pushed hard and the Himalayan mountaisn formed. suring this process, the surface f the earth rose, and the crust became thicker.

1 SOES1008 earth and ocean systems (30 decks)

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