[FINISHED] Tectonics
The core of the earth is around _______C, with heat left over from Big Bang and radioactive decay. Heat is unevenly distributed around the core, allowing ______________________ to be set up
7000, convection cells
Destructive (convergent) plate margins involve two plates coming together, with collision taking place. Each of ___ types of collision that take place are distinctive in terms of....
3, seismic/volcanic processes and resulting landforms
Continental areas of upper mantle (asthenosphere) is _____ to _______km deep
75, 300
Peru-Chile trench is _______km long, reaching depths of ___ to ___km below surrounding ocean floor - base is ____ to _____km below sea level. Have an asymmetric V-shaped cross-section, and are generally 50 to 100km in width
4500, 2,4
Oceanic areas of upper mantle (asthenosphere) is ____ to ______km deep
5, 200
Crust is the outer layer, ranging from ____ to _______ thick. Part of the ___________________
5, 300, Lithosphere
Oceanic-continental destructive: Trenches are generally ____ - _____km in width, and occur on ocean side of both island arcs and Andean-type mountain ranges
50, 100
Lehmann Discontinuity is ________km deep, and is a distinct boundary between materials of same composition but in different states. It is a zone of around ______km where rocks change from liquid in outer core, through liquid-solid mixture to an all solid......
5100, 100, inner core
Outer Core is _______ - ________km deep, made of liquid iron nickel. Liquid can exist as...
5100, 2900, pressure is less than that of inner core
The Inner Core is _____ - _______km deep, believed to be solid due to the extreme pressure - estimated to be ______m atmosphere (1atm at surface). Thought to be composed of iron and ___________, both heavy elements
6371, 5100, 3.6, nickel
Himalayas contains more peaks over ______m than anywhere else on earth, and extend for _________km
8000, 2900
Upper mantle is _____ - _____km. Made of solid silicates but less dense than lower mantle. Primarily made up of _________________, and contains the whole of the asthenosphere (as well as part of the _________________)
700, 35, peridotite, lithosphere
Oceanic-continental destructive: Trenches are deepest feature of an ocean basin, from _______m to _________m deep
7000, 11000
Deep ocean trenches are the deepest features of ocean basins - depth ranges from ______ to _______m. Most in the Pacific are formed of normal _______________ ocean crust, covered with thin layers of sediment/ash, making it easy to subduct under overriding plate.
7000, 11000, basaltic
Upper mantle has greater density compared to crust, by around _______g per cubic centimetre
0.3
Asthenosphere is hotter than lithosphere, at _______C vs ____C at top
1300, 20
From around AD________, it was noted that many continental coastlines appeared to fit together, especially those bordering _____________________. What looked like part of a jigsaw led to ______________________'s theory of continental drift
1450, Atlantic Ocean, Alfred Wegener
For Africa and South America, apparent polar wandering curves point in the same direction until _______Ma, then diverge after this - suggests there is one landmass up to them, and then split into two continents
150
Gondwanaland broke up in the Jurassic period (around _______ma), with fragments drifting apart to form the continents. Its former existence can be seen in the rocks of....
167, South America and Africa
Indian Ocean has the fastest MOR spreading rate of ____cm per year, and slowest is North Atlantic at ___cm per year
18, 2
Constructive (divergent) boundary: When South America separated from Africa _____m years ago, plate margin was in Gondwanaland. Supercontinent started to split along a major _______ system (similar to __________________________), and widespread extrusions of plateau basalts accompanies splits. As rift valley widened and subsided below sea level, ocean was allowed to flood in. As plate split completely, it was filled with ___________ and formed a new oceanic crust
180, rift, East African Rift, basalt
As oceans are growing larger, it is logical to assume earth is getting larger. However, no ocean floor is older than _____Ma, as at the edges of oceans there is an accompanying zone of subduction where crust is destroyed
200
Lower mantle is _______ - ______km deep. It is sold, with density highest near to...
2900, 700, the Gutenberg Discontinuity
Gutenberg Discontinuity is _______km deep. It is a very distinct and clear boundary, with material changing from metallic iron nickel to a stony ____________ material - state also changes from liquid (outer core) to solid (mantle)
2900, silicate
Fold mountain ranges around the world include the Andes, _______, Himalayas and ___________. They can be formed by either oceanic-continental or continental-continental collision, forming in a similar way. Land/_______________ rocks/sediments on ocean floor crumpled up to create a series of mountain ridges. Takes millions of years to form high mountains - intense heat/pressure from folding may cause rocks to be ______________________________
Alps, Rockies, sedimentary rocks, metamorphosed
Idea of convection cells originally set up by _________________ in 1928, with idea that slow-moving currents within the mantle move the overlying _______________________ plates with them. The cells are generated when hot, less dense material rises, flowing sideways and starting to cool (so becoming more dense and sinking)
Arthur Holmes, lithosphere
Oceanic-continental destructive: Sloping plane of boundary (as oceanic plate subducted) marked by increasingly deep-focus earthquakes (called the _____________________)
Benioff Zone
Example of fold mountains is India thrusting under ____________ to create Himalayan mountain chain - Mt Everest consists of marine sediments (e.g. ______________________)
Eurasia, limestone
Most plates are a combination of oceanic and continental crust - e.g. ______________ plate starts at Mid-Atlantic Ridge (oceanic) and extends across Europe/Asia (continental)
Eurasian
Many fossils are shared between continents - _________________ fern, ________________ reptile and __________________ reptile all have fossil remains in present day South America and Africa
Glossopteris, Mesosaurus, Cynognathus
______________________ itself spreads over several continents (incl. South America, Africa and Australia) suggesting that not only did some continents exist as one body, but they were one supercontinent - _________________
Glossopteris, Pangaea
As Pangaea split in two, it formed ___________________________ in the South (including South America, Africa, Antarctica, India and Australia) and _________________ in the North
Gondwanaland, Laurasia
Himalayas formed when India split from ______________________ and moved north towards Asia - collides, subducting ____________ ocean and forming trench and volcanic arc.
Gondwanaland, Tethys
Geologist __________________ proposed theory of sea floor spreading in early 1960's - basaltic magma from mantle rises to the surface to create new ocean floor at _____________________. As ocean becomes wider, continents drift apart.
Harry Hess, mid-ocean ridges
Until 1960's, no one knew how continents had moved - continental drift was an unproven theory. Evidence for sea floor spreading emerged around this time with development of _______________ - maps of sea floor by ships showed areas of towering mountains under sea and areas of plunging trenches (up to _____km deep, compared to Everest at ____km high)
SONAR, 12, 8
______________________ reptile and ________________________ reptile are weak swimmers, so there would be no way they could inhabit several continents unless they were attached
Lystrosaurus, Cynognathus
Example of hot spot is Hawaiian Islands - formed island such as _______ and _____________ (___________________ volcano) - up to _________m from ocean floor. Moves northwest at around ____cm per year, with _________ next to form (new submarine volcano, surfacing in around 200,000 years)
Maui, Hawaii, Mauna Loa, 5000, 5, Loihi
When a convection current rises to the surface at a divergent plate margin/hot spot, there is new land created (e.g........), eruption of lava/magma and gas vents
Mid-Atlantic Ridge
Crust and upper mantle divided by the...
Mohorovich discontinuity
Example of Oceanic-continental destructive boundary is...
Nazca plate and south american plate
Antilles Island Arc formed due to subduction of ____________ plate under ___________________ plate at the ______________________ trench - islands such as...
North American, Caribbean, Puerto Rico, Montserrat
Alfred Wegener proposed that there used to be a single land mass, _____________, and explained this through his theory. However, at the time many Earth Scientists did not believe his theory as there was no known mechanism by which continents could move. Since then, however, sea floor spreading has been discovered using __________________________
Pangaea, palaeomagnetism
Oceanic-continental destructive: Example of deep ocean trench is _____________________ (4500km long, __ - ___km below surrounding ocean floor)
Peru-Chile, 2, 4
Fold mountain chains are hundreds of km long - can be seen how one _______________ fold mountain chain in Gondwanaland crosses from Africa to South America and back to Africa as a continuous belt - must have been joined together in past
Precambrian
Mt Everest has ______________________ limestone, originally part of the _____________ Ocean, at 8462m high
Yellow Band, Tethys
Plate boundaries/margins between lithospheric plates are zones of activity, whereas areas within plates are ____________ (i.e. geologically inactive). As plates move towards/away from each other, MOR's are formed and crust is melted at ______________________ zones
aseismic, subduction
Continental-continental destructive (collision): Base of crust melts due to proximity to ________________________ and large plumes of viscous _______________ magma intrude themselves into overlying crust - do not make it to surface as extremely viscous. No volcanism.
asthenosphere, granitic
Top of a fold (looks like an arch) is called the...
anticline
Hot spots occur as...
a concentration of radioactive elements in the mantle causes a hot plume of magma
Diapir is...
an intrusion in which a more mobile/ductile material is forced into brittle overlying rocks
Slow-moving currents in the ________________ (or possibly whole mantle) move overlying _________________ plates with them. Convection cells lift lower density material upwards, then sideways when it can rise no more and starts to cool down (then sinks as it becomes more dense).
asthenosphere, lithospheric
Theory that mid-ocean ridges in centre of all ocean basins have an ____________________ in the middle (deep valley with steep-sided mountains either side). When the MOR rises above sea level, it can form islands such as ___________ (Mid-Atlantic Ride). Nearest the ridge, the crust is hot and expanded, so ridge is formed. Further way, crust cools and _______________, creating flatter areas of ocean basin
axial rift, Iceland, contracts
In both South America and Africa, there are sedimentary deposits of angular, poorly sorted and scratched pebbles (______________) in a fine-grained matrix. This is fossil boulder clay/______________ deposited by an ice sheet that existed in the carboniferous (______Ma)
clasts, tillite, 300
At the boundaries between mantle/core etc., there are distinct changes in...
composition/physical properties
Three possible explanations for movement of tectonic plates (although no definitive answer) are.....
convection cells, ridge push, slab pull (at subduction zones)
Gravity pulls subducted oceanic plates down into the mantle at __________________ boundaries, which may be the key force for plate movement. The weight of cold, dense ___________________ sinking downwards at ocean trenches pulls the rest of the plate with it - known as....
convergent, lithosphere, slab pull
Iron-rich materials in some rocks can hold a record of the Earth's magnetic field at time of formation. These rocks can be collected and ______________, and direction of _____________________________ measured - plot as an apparent polar wandering curve.
dated, palaeomagnetism
Where two lateral currents meet at a subduction zone, either one or both start to sink as they are cooler/denser, causing _________________________ (around _____km down), fold mountains (e.g. ________________) and lower levels of heat flow
deep ocean trenches, 11, Andes
During Earth's formation, when planet was molten, heavier/_____________ minerals/elements sank and concentrated as the core
denser
Oceanic-oceanic destructive: similar to oceanic-continental, but _____________/older of two ocean plates sinks instead. No continental crust to melt, so rising magma less viscous and _____________________ in composition - semi-explosive volcanoes. Rising magma forms an arc of volcanic islands, called ____________________ - e.g. Antilles in the Caribbean.
denser, intermediate, island arcs
Categories of plate margins are...
destructive (convergent), constructive (divergent), conservative
Strongly rising plume could be called a ____________ - when this reaches under the lithosphere, it can diverge into a _____________________, causing widespread melt and pushing through to form volcanoes
diapir, bulbous head
Rising magma injected along MOR at _____________ margins forcibly pushes plates apart. Sheeted ____________ found on either side of ridge axis are evidence of this. Some believe this idea of ridge-push is flawed as tension is the key force at the ridge, and it may be accurate to describe this process as ______________________________ of the ridge (given their height)
divergent, dykes, graviational slide
Plate tectonics brings together the idea of continental drift and sea floor spreading, giving a coherent explanation for events such as...
earthquakes, volcanoes, faults, folds and fold mountains
Beside ridges, magnetism of basaltic rocks can be measured to prove sea floor spreading - as basalts are _____________, they cool and become weakly magnetised, showing direction and strength of Earth's magnetic field at time of solidification
extruded
Gondwanaland and Laurasia shared rock types and fossils as, when it was Pangaea, it was ___________________ at the same time
glaciated
Layers/boundaries of the earth are...
inner core, lehmann discontinuity, outer core, gutenberg discontinuity, lower mantle, upper mantle, crust
Evidence of continental drift includes...
jigsaw fit, rock types, mountain chain, fossils, glaciation, palaeomagnetism
The crust is a cold, solid rock that forms a thin layer of the....
least dense rock
Plate tectonics suggests uppermost layer of Earth is divided into number of sections (rigid __________________________), which are constantly in motion relative to each other, carried by moving material beneath (the ______________________, which is partially melted and acts as a rheid)
lithosphere plates, plastic asthenosphere
divergent plate margins occur as rising convection currents in mantle push up and move along bottom of ___________________, flowing sideways beneath it. Lateral flow causes lithosphere plate to be dragged in direction of flow - as currents spread from central rift, they cool by ___________________ and become elastic, so easier to move overlying plate
lithosphere, conduction
Oceanic-continental destructive: Temperature increases with depth, so partial melting of crust as it's subducted. Melted minerals separate and begin to rise as _________ as they are less dense than surrounding rocks
magma
Oceanic crust (lithosphere) is rich in Iron and ______________________. May form basalt pillow lavas, and dolerite may form ___________, and there may be _________ in layers. Density of around ______g per cubic centimetre, with oldest crust being ________Ma. Thickness of 5-10km (average 7km)
magnesium, dykes, gabbro, 2.9, 200
area of particularly strong rising heat in mantle could be called a...
mantle plume
During Earth's formation, when planet was molten, lighter materials developed into the _______________, which makes up _____% of the Earth
mantle, 99
Types of destructive (convergent) plate margins include...
oceanic-continental, oceanic-oceanic, continental-continental
Oceanic-continental destructive: Compression of continental crust and sediments scraped off at subducting plates (_________________) form huge chains of fold mountains. lots of _______________________ happen too, where rocks melt and solidify with new properties
ophiolites, metamorphoses
To prove that two rocks on either side of an ocean are of the same ________________, they must have the same physical features, chemical composition and be the same age - determined by ________________________. Many matching rocks have been found - __________________ in N. South America and NW/Central Africa, carboniferous coals and _____________
outcrop, radiometric dating, Precambrian cratons, tillites
Asthenosphere is the part of the mantle which is __________________________. Most of the mantle behaves as a ________. Temperature is high, particularly between ____ - ______km at around 1300C, enough for around _____% of peridotite crystals to melt - this causes a film of melted materials to surround each solid crystal, allowing...
partially melted, rheid, 75, 250, 5, mantle to flow more easily
As interior of earth is extremely hot (due mainly to ongoing decay of ______________________ in core), convection currents can begin - occurs if more heat generated in one area than another
radioactive elements
Nowadays, ocean floor basalts can be ___________________________ to give a series of absolute dates from which rate of spreading can be calculated, which is conclusive proof for sea floor spreading
radiometrically dated
Basalts show normal and ______________ polarity in opposite patterns of strips either side of ridges, suggesting basalts were intruded into the ridge, then magnetised and breaking in two before moving apart. They form a _________________ pattern on sea floor parallel to MOR - zones are not all the same width, as they vary with length of time during which magnetic field stayed in one direction/amount of ________________ during any particular period
reversed, symmetrical, lava erupted
Constructive (divergent) boundary: where plates are moving apart, seen through the world at MOR's (form _________________ in continental crust, but MOR at oceanic).
rift valleys
Lithosphere is when mantle is cool enough to prevent partial melting near surface - zone is _________ and brittle like the crust. Shares the same chemical properties as the mantle, but cannot flow - carried by _______________________ below. Broken into plates due to brittleness, with outermost skin of the lithosphere being the ______________ - separated from the mantle lithosphere by the....
rigid, asthenosphere, crust, Mohorovich discontinuity
When currents rise to the surface, there is...
rising magma and eruptions
near the top of the asthenosphere, the current stops rising and spreads laterally on either side of Mid-Ocean ridge, resulting in _________________________. Beneath the lithosphere, partial melt (around ____%) in the asthenosphere reduces friction and acts like a lubricant
sea floor spreading, 5
Oceanic-continental destructive: Friction causes continental crust to melt and huge plumes of ____________________ rise and solidify as _________________________
silicic magma, granite batholiths
Continental crust (lithosphere) is rich in aluminium and _____________, with granite rocks, as well as deformed igneous/____________________/sedimentary rocks. Average density of _____g per cubic centimetre, with oldest crust being _______Ma. Thickness of up to 90km under highest mountains (average 35km)
silicon, metamorphic, 2.7, 400
Oceanic-continental destructive: oceanic crust is denser than continental, so oceanic crust ___________________ continental crust (subduction) - _______________________ occurs at this point
sinks below, deep ocean trench
If continents were not joined together, there would be no way all were glaciated at the same time. Glacial _________________ can be used to trace movement of all glaciers to a common source area in Central Southern Africa too (likely __________________ occupied a position near to the South Pole)
striations, Gondwanaland
Continental-continental destructive (collision): neither plate is dense enough to ___________ so, as one goes under the other, the crust becomes more buoyant and so thrusts it up. This forms enormous...
subduct, fold mountains
When convection currents sink, there is...
subduction zone/deep ocean trench
Island arcs are not on a line as time is needed for...
sufficient heat to melt plate
Bottom of a fold (looks like a 'u' is called the...
syncline
Isostasy is...
the state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density
There are simple folds, and Fold moutains can have much more complicated folding such as __________________/overthrust - rocks become so twisted.bent that they crack and...
thrust faults, top half of anticline thrusts over the bottom
crests of mid-ocean ridges are often offset by large faults called ________________________ - these are not fully understood but have something to do with plate splintering when MOR is pulled apart, due to....
transform faults, curvature of earth
Oceanic-continental destructive: Rising magma at a high enough temperature to melt some surrounding continental crust, making magma more _______________ (so volcanoes will be explosive). __________________________ of Andes are an example
viscous, stratovolcanoes
Hot spots rise and eat into plate above, breaking through to the surface eventually to form ____________________. As the ocean floor moves over this hot spot at about ______ inches per year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate
volcanoes, 5
If Africa/S. America etc. had always been separate, they should have different fossil records (particularly animals/plants living on land or shallow sea floors, as.......)
would be unable to cross ocean
