Plate Tectonics Flashcards
What is the outermost layer of the Earth and its thickness?
The crust is the outermost layer with a thickness of 5km under oceans 40 km under continents and 65 km under tall mountains
What is the composition of earths crust (continental vs oceanic comp)?
Continental Crust consists mostly of granitic rock, which is felsic and rich in silica, with a p-velocity of 6km/s and a density of 2.8g/cm^3, compares to Oceanic Crust consisting of basalt and gabbro, mafic (iron) with a p-velocity of 7km/s and a density of 2.9g/cm^3
What happens to p-velocity below the earths crust and why?
P-velocity increases to 8km/s, which indicates a sharp boundary between crustal rocks and underlying mantle. This indicated denser ultramafic rock Peridotite
What is the name for the boundary in between the crust and Mantle?
Mohorovicic discontinuity (moho)
What percentage of the earths crust is above sea level?
29.2%, 70.8% is below sea level
What does the upper mantle rock consist of and what is its average density?
Mainly peridotite (olivine and pyroxene, the two silicates of iron and magnesium) average density is 3.3 gm/cm^3
What changes about olivine and pyroxene in the upper mantle?
Their internal atomic structure changes in Properties and Forms with changes in temperature and pressure… Upper mantle causes them to begin to melt, deeper down increased pressure causes these minerals to compact- Both these process occur in the mantle
What is the outer and inner core composed of?
Outer: iron, molten Inner: solid
What is the core- Mantle boundary called and what are its properties?
The D layer, 200km thick, drop in p-velocity in the bottom 20km
How could earth be classified with respect to its physical properties/ mechanical layers (different than other classification)?
Strong: in the same sense as ceramic material, rigid and easily deformed, also can crack
Weak: like modeling clay/wax… ductile
What is included in the lithosphere?
The CRUST and the top part of the MANTLE
What are the physical properties of the lithosphere?
strong, nonflowable, solid outermost shell. It’s thinnest is oceans (around 100km at thickest point) and ticker under continents (thicker than 100km), rides on the solid, weak asthenosphere
What are the physical properties of the asthenosphere?
weak solid (sort of soft) because its almost at the melting point, lies between 100-150km and 300km deep, acts like a ductile solid
What is Isostasy?
State of gravitational equilibrium in between the earths mantle and crust where the crust floats at an elevation that depends on its thickness… think of it like an iceberg floating in the sea
Where is the low velocity zone with regard to p-waves
P-wave velocity generally increases in velocity at greater depths. The low velocity zone is between 100-200 meters, p-wave velocity decreases in this zone
Define Geotherm
indicates the change in temperature as depth increases
What does the Melting Curve indicate?
the temperature at which materials melt as depth increases in earth
What is the geotherm gradient?
It’s the rate of change in temperature in relation to depth (ie 20 C/km)
Where does melting occur, with respect to the relation between geotherm and the melting curve?
Melting occurs when geotherm lies to the right of the melting curve
Divergent Boundaries
Where pates separate and move in opposite direction, which allows for new lithosphere to form through the process of upwelling
Convergent Boundaries
Form where plates collide— one goes beneath the other, existing lithosphere is returned to the interior
Transform Fault Boundary
Plates slide past each other, approximately at right angles to their divergent boundaries
How does an egg relate to the lithosphere?
Its not a continuous shell, rather broken, rigid plates, in motion on top of the asthenosphere
Which divergent boundary has the quickest spreading rate?
The East Pacific Ridge
Which divergent boundary’s have slow spreading rates?
The Mid Atlantic Ridge, the Southwest Indian Ridge, and the Mid-Indian Ridge
What is the relationship between rocks proximity to divergent axis, and rock age?
Rocks are progressively older, colder and at lower elevations than rocks closer to the axis of the ridge
Describe the characteristics of continental plate?
Characterized by down faulted rift valleys, basaltic volcanic activity, and shallow focus earthquakes
Identify the significant continental plate separation zones
The great Rift Valley of East Africa, the Rhine Valley of Europe, the Red Sea (Arabia/Africa), Gulf of California, Iceland (mid atlantic ridge) not soo significant…
What physical process takes place at convergent boundaries?
Subduction, one plate sinks beneath the other, oceanic lithosphere descends into the asthenosphere
Name the important characteristics of convergent boundaries
Subduction, deep sea trench’s 100 km wide where oceans reach its deepest point of 10 km, a mountain chain created by the uplifted plate parallel to the trench, earthquakes, materials scraped off the descending plate that don’t seem to belong to their surroundings, volcanism
What are the characteristics of ocean- ocean plate subduction?
deep-sea trench, volcanic island arc, shallow and deep focus earthquakes, accretionary wedge, forearc basin
What are the characteristics of ocean-continental plate subduction?
deep sea trench, volcanic belt at edge of continent, shallow and medium focus earthquakes, melange deposits, metamorphism
What are the characteristics of continent-continent plate subduction?
suture zone marking boundary where plates are welded, multiple thrusting, thickening of continental crust, high mountains, melange, ophiolites
Define melange
deformed and metamorphosed shallow and deep ocean sediments
Define ophiolites
assemblage of mafic plus ultramafic rocks, likely fragments of oceanic lithosphere tectonically places on continental margins… occurs on collisional mountain belts/ island arcs, and define the Structure Zone, where two plates have welded together
What is the rock composition of volcanic island arc’s?
Mafic, to intermediate
Identify the deepest ever trench
The mariana trench, in Japan
Why do volcanoes occur in subduction zones?
As the one plate sinks into the mantle, its less dense portions rise and form Peridotite (ultramafic melt) which feeds volcanos
SLIDE NOTICE FOR MORE INFO
See slides for detailed models of subduction
What is a famous example of convergent continent- continent boundaries?
The Himalayas
Identify the San Andreas fault
it is a transform fault boundary (right lateral strike slip fault) in which the pacific plate slides past the North American Plate in a northwesterly direction
Transform Fault Boundaries
two pates slip past each other, no volcanism, shallow focus earthquakes, lithosphere is neither destroyed nor created
Identify the relationship between magnetism and plate tectonics
Magnetism is used as evidence for plate tectonic theory.. magnetic bands, as they experience a period of normal magnetism, followed by a period of reverse magnetism, followed by a period of normal magnetism
SLIDE NOTE
see Intraplate volcanism slide for examples (if you have time, there are a lot)
