2. paleontology - fossils of things that canot swim or fly found across vast oceans
3. topography- folded mountain belts that end at one continent and begin on another.
4. glacial deposits - movement of glaciers leave distinct marks showing movement at the equator.
5. paleoclimatic belts - things formed only in warm climates are found in acient rocks at the poles (coal, limestone from coral)
sea floor spreading - what where why how
at MOR tension pulls the rock appart, magnetic patterns are recorded in the new earth, this is the driving mechanism for continental drift.
geodynamo & earth magnetism
spinning electricly conductive (Fe) fluid creates a magnetic field.
magnetic minerals align in new basalt to record the location of these magnetic poles. evidence of continetal drift and polar wander
details of magnetic stripping
faster ridges - thicker stripes
less reversal thicker stripes
paleo magnetism what and why?
record of the magnetic pole recorded in rocks of different ages
provides a history of continetal movement
how do we know a rock formed near the equator?
magnetic mineral aling in higher inclanation near the poles and lower almost horizontal inclanations near the equator
what are polar wander paths? what can they tell us?
Over time the poles appear to wander all over the place specific to each continent
if we account for continental drift/seafloor spreading they will in fact line up to a comon pole
plates & lithosphere vs athenosphere
plates are made of the rigid lithosphere, these "float" on the asthenosphere
convection - is it the driving force of drift/spreading?
NO!convection of the asthenospher is caused from the conductive cooling of the lithosphere.
rather the driving force is older cooler more dense oceanic crust subducts and creates tension which pulls apart the MOR. As the crust at the MOR becomes thiner it sinks creating the valley in the middle. (on continets this is the rift valley)
So what controls the rate of sea floor spreading?
which moves faster?
The pacific moves much faster ~15cm/yr vs atlantic ~4cm/year
this is because 1) it is older/more dense thus more "ready" to subduct. Also it surrounded by more subduction zones, thus there is more room for it to disapear...this is why there is the pacific ring of fire while the atlantic is calm volcanism.
why cant all plates expand?
It would make the earth huge and hollow.
anaology for spped of plate spread
finger nail growth
how do we study the sea floor
samples from ocean drilling
what is an ophiolite?
ancient oceanic crust exposed on land.
what is an absyssal plain?
areas of the sea fllor 3-6km deep, inactive, high sedimentation. typically the area from the edge of the continetal slope to the MOR
what is the realtion ship between temperature and pressure
the melting point increases with pressure
i.e. it takes higher temperature to melt rocks under great pressure.
THIS IS WHY THE INNER CORE IS SOLID!
is a MOR active or passive?
It has active volcanism however it is a passive mantel upwelling.
dip angle - tell me about it
this is the angle between the overiding(continetal plate) and the subducting plate.
the older/denser a oceanic plate is the faster it subducts/the greater the dip angle.
how do new oceans form?
at continental rift valleys
tensions pulls and thins the plate, thus it begins to sink, this continues until a large basin forms...the red sea
what is the role of H2O in plate tectonics
cold water sinks into cracks in the plate near a MOR. this water is heated, becomes element rich, some of it is expelled near the MOR (smokers)...
Some water stays in the plate (bound in rock) and is cariied all the way to the subduction zone where it is realeased (through melting of the subducting plate)
the water is hot and more bouyant so it rises into the overiding plate, lowering the pressure, allowing for melting, thus the volcanic belts like cascades, and why the eruptions are so explosive.
one "ocean volume" of water is recycled_________through the hydrothermal/ridge interaction
every 100 mil year
how does a continent grow? 2 ways
1. by area - continents colide, india nad the himalaya
2.by mass - new magma from sub zone. Hydrous minerals help to create differeing composition
what is the difference between stress and strain?
stress is the force strain is the result
i.e. stress creates strain
examples of convergent plate boundries
rockies, alps, andes, himalayas
adjustment due to gravity
crust bouyant, mantel dense
iceberg/log in water analogy
brittle vs ductile
what determines it
brittle lose cohesion breaks/fractures
ductile perment lose of shape but doesnt break...it folds
Presure(depth) & strain rate
silly putty analogy
units in pascal
g=gravity 9.8 m/s2
z= depth (m) 30,000m
three types of faults
1. normal - tension/pulling = verticle movement, hang wall down
2.reverse - compression/pushing hang wall up
3. slip lateral slide
rule of thumb for depth & pressure
3km = 1000bars = 1kbar = 0.1 gpa
what is the benioff zone?
area of subduction zone where deep earthquakes happen....proved subduction zones
earth quakes related to the three types of plate boundries
1. divergent - shallow narrow zone ~15km
2. transform - shallow
3. convergent - wider belt shallow, int, and deep D>100km
focus vs epicenter
foucus is exact point
epicenter is verticle translation to the crust
why are quakes in the upper 70km
because rocks under greater pressure are stronger. also more ductile