The plate tectonism is a
revolutionary idea, which grew up with me. (Started in the 1960ís)
Oceanic Ridge, or divergent plate boundary
Lots of people in the late last century and
early this century realized that in the middle of the oceans there is a deep
ridge system, which they called mid-oceanic ridge.
How do grabens form?
1.In the mantle there are big convection
cells, along which there is a heatflow.
2.Along the upwelling side (mantle plumes)
the temperature is relative high which starts a partial melting in the mantle.
3.Because of the volume of the liquid phase
is larger it needs larger space, which will initiate a triple junction with
three radiating cracks the normal faults.
One plate is subducted under an other and
adventually resorbed in the astenosphere.
Oceanic -Oceanic boundary
When two oceanic plates converge one of them
is subducted under the other one, and we call it oceanic-oceanic boundar
As the subducting plate descends into the
mantle it gets hot and starts to melt partially generating an andesitic magma.
This magma is less dense and rises to the surface to form a chain of volcanic
islands called volcanic island arc.
This arc is nearly parallel with the
Japan island chain, Philippine island region
are all result of this.
The oceanic plate will subduct underneath
the continental (more dense)!!!!!! (Continental plate will never subduct!!!!!!!!)
The magma chain forming here is also called
volcanic arc, representing the nonsubducting plate, and also composed of
The Peru-Chile trench, Andes are the
resulting volcanic chain
3.Continental-continental or collisional plate boundaries
The continents getting closer to each other
as the oceanic crust becomes subducted. When two continents meet none of them
can sink into the mantle, because continental is much more less dense, than
Mountains are the suture zones of ancient
Ancient convergent zones
Intensely deformed zones, even after the
erosion of ancient mountains
Melange ---- mixed rocks
Slices of oceanic crust (ophiolite)
Appalachians, Alps, Hymalayas
Plates laterally past each other.
Lithosphere is neither forming, nor
consumed, because of the intense friction, lots of shallow earthquake.
Best known is San Andreas!!!!!
Scientists figured, that there is a cycle in
the plate tectonics called Wilson cycle. Wilson cycle always strats with a
supercontinent (Pangea is the last we had), which then brakes up!!!!!
Evidence for this is that there is no older seafloor than 200 million years.
After breaking up, the continents later will
get together again, making a new supercontinent with newly formed mountains on
it showing the suture of the earlier smaller continents..
Plate tectonics and Mountain building
Episode of intense rock deformation or
mountain building. Along subduction and collision zones.
Subsidence of plates and the accumulation of sediments
of exeptionally thick sediments vary greatly in size, shape and tectonic
setting, but they are collectivelly referred as sedimentary
accumulation of sediment in a sedimentary basin requires space, which can be
produce either by subsidence or by sealevel rise or both.
depression of one lithosphere plate as it is subducted beneath another.
This result in the long narrow, deep topographic trench on the sea floor.
Thermal or cooling subsidence
is caused by the cooling of lithosphere plate as it moves away from the hot
spreading ridge. The cooling material becames more dense and subside into the
mantle. This create space for the accumulating sediment.
Sediment loading subsidence
accumulation of sediment can also weigh down a lithosphere plate
shoving of huge slab of sediments or rock over an other one.
movement after melting ice slab.
deepwater sediment, overlying basalt
gravel, sand mud derived from volcani, granitic metamorphic rocks
gravel, sand derived from orogenic belt
river and deltaic
q-rich sands and limestone, mud, evaporites, coal
marine with deltaic
limestone, seaward shale
marine shelf to deeper marine
gravel and sand, prob. with evaporites and limestone
and lakes, changing to shallow marine