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Define plate tectonics
Theory explaining appearnce & dynamics of ocean floor & continents.
What's another word for lithospheric plates?
Name the layers of Earth's structure: what is it dependent on?
- 1. Core
- 2. Lower mantle
- 3. Upper mantle (Asthenosphere)
- 4. Lithosphere
Are all ocean crusts covered with water?
Which is denser: ocean crust or continental crust? Why?Which floats lower?
Ocean crust - floats lower, bc of higher density (composition)
What is a convection cell?
Circulatory system established by convection: fluid warms --> rises --> displaced by new upwelled fluid --> cools --> sinks to be reheated.
Upwell & downwell
Define hotspot and its impact on the movement of lithospheric plates
Surface expression of persistent convection plume of molten mantle material rising to Earth's surface.
Which is older? Oceanic crust or continental? Why?
Continental! Because new oceanic crust is always being formed at mid-ocean spreading centers, bc its thinner and magma can potentially well up through.
Where is the slowest spreading center in the world located?
Didn't know there was spreading center there for the longest time.
Why is Antarctica so difficult to study?
Covered with ice.
Where do most earthquakes occur? What causes earthquakes?
On plate boundaries.
Faulting - a sudden lateral/vertical movement of rock along a break surface.
This is bc tectonic plates are moving past each other slowly, but the edges are jagged, so they are caught at a certain point.
But! Plates keep moving, so at a certain point, a lot of energy is built up and rocks that are caught with each other break causing earthquake.
Why are Appalachians shorter than Himalayans if formed from same type of plate movements?
Continental collision - bc Appalachians have undergone more erosion
What is a deep trench parallel to the coast characteristic of?
Continental convergent margin - ocean crust subducting under continental crust
What are characteristics of continental convergent margins? (
- - DEEP TRENCH PARALLEL TO COAST
- - Coastal mountains (formed from ocean sediments and sedimentary rocks - have lower density like continental rocks), so are scraped off, compressed, folded, and lifted.
- - Volcanoes - form on continental crust on less dense plate from subduction of oceanic crust. (1) As it goes deeper, it melts, mixing with heated water and sediments. (2) The magma rises to form volcanoes near edge of continental plate. As magma erupts, pressure decreases and water and other constituents that are released by the heating of subducted crust and sediment become gaseous and expand rapidly -> explosion.
What are examples of:
1. Continental collision margins?
2. Continental convergent margins?
3. Continental divergent margins?
4. Oceanic convergent?
5. Oceanic divergent?
Name characteristics too
1. Continental collision margins? Himalayas/Appalachians; extreme mountain building
2. Continental convergent margins? West Coast of North America and South America; deep trench parallel to coast, coastal mountains, volcanoes
- 3. Continental divergent margins? Red Sea, Pacific Ocean - central rift valley, ocean formation (ex. East African Rift)
- 4. Oceanic convergent? Indonesian/Mariana islands - volcanic island arc, trench, maybe low islands from accretion of sediments.
5. Oceanic divergent? Ex. Mid Atlantic Ridge, seafloor spreading - mid-ocean ridge, central rift valley, fracture zone (leads to tsunamis) hydrothermal vents!!!!
Where are hydrothermal vents found?
What role do transform faults play? How are they formed?
They make it possible to add/destroy plate material at different rates to accommodate varying rate of new ocean crust spreading/creation.
A transform fault is formed between two different plates, each moving away from the spreading center of a divergent plate boundary.
Why are earthquakes located at faults? What don't faults create?
Because motions of plates at transform faults create complicated stresses --> jagged edges catch, hold, then break off creating earthquakes
Don't make volcanoes, mountains, trenches, etc.
What are good conditions for reef? Where are reefs found?
Low turbidity, shallow/warm water.
In former passive margins and around hotspots - as lithospheric plates/hotspots move in relation to each other, volcanic islands form --> forming coral reefs (little runoff of freshwater/sediment) --> then when hotspot moves, volcanic island cools, gets more dense, then sinks, leaving behind a ring of coral reef.
What would happen if inner core spun at same rate as outer core? (4)
- 1. No geomagnetic barrier from sun
- 2. No paleomagnetic reversals
- 3. No polar wandering bc no magnetic fields to begin with
- 4. No driving force for plate tectonic movement (spreading cycle)
Where are many (not all) hotspots found?
Where convection plumes upwell from deep mantle
How long has our current spreading cycle been going on?
225 mil years
What is responsible for topography and natural disasters on Earth?
interactions of plate boundaries
How does a volcano form?
- 1. Oceanic plate subducts under less dense plate (continental/oceanic)
- 2. Marine sediments get dragged under water, melt, lower MP of underlying magma, which becomes less dense than rock above it.
- 3. Bc of smaller density, pressure builds leading to eruption (either violent/nonviolent) of magma.
Define biogenic sediments
sediments pertaining to material of biological origin; sediments in which at least 30% was from a biological creature
- Found in high T and high productivity areas usually further in ocean (except calcareous - which does well on coast)
Define lithogenic sediments
Sediments that contain at least 30% of lithogenous material (terrigenic/red clay/etc) eroded from land or silt/mud deposits from river.
Lithogenic sediments are found closer to coasts, on glaciers, etc.
Where are authigenic sediments found? Another word? Define them
Authigenic - sediments composed of solid materials formed by chemical precipitation from seawater.
Found in deep sea, but in small amounts, as mostly overwhelmed by biogenic/lithogenic particles
What is the importance of studying marine sediments?
- Marine sediments preserve history of biogeochemical cycles: volcanic explosions, land erosions due to sea level, glaciation changes, important for seeing effects of pollution
Sediment deposit formed by turbidity currents with heavy stones on bottom with progressively finer grains on top, with fine-sand in between layers.
Found in abyssal plains
What are some origins of biogenic sediments? Calcareous (6)
- 1. Fecal pellets (must be heavy/sink quickly so not eaten)
- 2. Larvacean houses
- 3. Eukaryotic phytoplankton, zooplankton (single-celled algae, animals like molluscs)
Origins of biogenic material? (silaceous)
- 1. Eukaryotic zooplankton (single-celled protists)
- 2. Eukaryotic phytoplankton (single-celled algae)
Which type of biogenic origin only substantially precipitates in highly productive, tropical waters?
Eu zooplankton (single-celled protists)
Where do siliceous sediments do best? How about calcareous?
Siliceous - deep, cool surface water in polar areas (except for the eu zooplankton - single celled protist)
Calcareous - shallow, warm waters (high T, low P, low CO2 concentration) - near equator
Where do high and low rates of sedimentation occur? 2 each.
- High - continental shelves, older crust (continental)
- Low - coincide with red clay in abyssal plains, newer crust (oceanic)
What is the difference between Atlantic and Pacific ocean in terms of sedimentation rate? (4)
- 1. Atlantic --> higher sedimentation
- 2. Atlantic --> deeper CCD due to lower CO2 content, more likely to find filled trenches (due to turbidity currents), bc Atlantic formed before its subduction zone did.
- 3. Pacific --> more CO2 content due to global circulation patterns
What does the lithosphere consist of?
upper mantle and crust
Upper layer of mantle right underneath lithosphere
Example of important cosmogenic sediment?
Meteorite that created Chixulub crater in Yucatan Peninsula
What contributes to CCD?
- Calcium Carbonate Compensation Depth
- The depth of water underwhich most CaCO3 is dissolved and there is no trace of sediments.
This is bc of low T, high P, and high conc of CO2 (whose solubility increases with depth)
Caused by: 3
Long, narrow deep depression in oncean floor formed by divergent oceanic, continental convergent, and transform movement
The part of earth that is between lithosphere and core
Define hot spot
Hotspot - surface expression of persistant convection plume of molten mantle material rising to Earth's crust, melting crust, and spilling out in form of volcanoes
Isostatic vs Eustatic sea level change? 2, 4
- Isostatic - local change in sea level - 1. glacial rebounding, 2. tectonic uplifting of coastal regions (i.e. CA)
- Eustatic - global change in sea level - 1. Melting of ice caps 2. thermal expanion of sea after last ice age 3. Rising sea level due to seafloor spreading 4. Repositioning of continents by continental drift - lower sea level.
Created by oceanic divergent margins, but also by convection cells --> upwelling magma rises, melts through crust, spews out and then cools in form of underwater volcanoes/mountains.
Shaped like bell curve
Oldest crust is on edges farthest from ridge
Subduction zone = area in which lithospheric plate is descending into asthenosphere
Define Paleomagnetic reversal
Record of past orientation of earth's magnetic field anomalies in rocks
Barrier island migration
As sea levels rise, storm winds can blow sand of barrier island to opposite side shifting barrier island inwards. Vegetation will shift too.
Define overwash and longshore transport
Overwash - flow of water/sediment over crest of beach that doesn't immediately return (overwash fans)
Longshore transport - aka littoral drift - sediment transport parallel to beach within region from breaker zone to top of swash line.
What are specific examples of evidence supporting theory of plate tectonics?
- 1. Fit of continents
- 2. Identical fossils on opposite sides of oceans
- 3. Paleomagnetic reversals in mid-ocean ridge
- 4. Direct measurements of plate margins
- 5. Volcanoes and Earthquakes located along oceanic ridges with BALSALTIC lava.
- 6. Location of hotspots - and trail of hotspot islands left behind as hotspots and plates move in relation to each other
- 7. Hetereogeneity of Earth's mantle
Name the 5 types of marine sediments
- 1. Lithogenic
- 2. Biogenic
- 3. Authigenic (hydrogenic)
- 4. Volcanogenic
- 5. Cosmogenic
What dose sediment distribution depend on? (9)
- 1. Ocean temperature, pressure,
- 2. Ocean pH
- 3. Size of sediment
- 4. Wave (orbital velocity)
- 5. Cohesion of particles (i.e. clay)
- 6. Turbidity currents
- 7. Little lithogenic sediment is trasnported offshore beyond longshore drift system
- 8. Component
- 9. Ocean
What phenomena do plate tectonics explain?
- orogenesis - mtn building
- volcanoes and earthquakes
- continental drift
- evolution of climate
- divergen evolution from separate evolution
Where are ooids found? Made of?
Warm, shallow waters - CaCO3 precipitation
Why does CO2 concentration increase with depth? (3)
- 1. Low T, High P --> more soluble
- 2. No photosynthesis to remove CO2
- 3. May be increased by decomposition or animal erspiration.
How does a low ocean pH affect coral reefs and shellfish?
Coral reefs/shellfish structures are made from CaCO3. If pH is low, then little calcium carbonate will be intact for coral reefs and shellfish to use to build and maintain shells/skeletons.
Which is generally higher in ocean waters? Pteropod mud or foraminiferal mud?
Pteropod relative to CCD than foraminiferal mud bc CaCO3 in pteropod ooze is made from more soluble form of CaCO3 than foraminifieral
What are four pieces of evidence of past glacial extent?
- 1. Glacial moraines - number of ridges can determine number of ice ages, can determine extent of last glaciation if topography still exists on moraine
- 2. Erratics - rocks that are generally found in a certain type of geography are found elsewhere due to transport by glacier.
- 3. Amount of 18O:16O in marine sediments from deep ocean drilling - more 18O means more 16O was in glaciers --> lots of glaciation.
- 4. Glacial rebound - continents (like North America) are slowly rising after the weight of heavy ice has been melted off.