Ultimately, this will be a chapter on isotopes...
This exercise will help you to understand how isotopes are interpreted and their relative abundances utilised to determine palaeo-environments.
Spreading Rates
Velocity equals the distance moved in for a unit of time. Spreading rates for
the oceanic plates are measured in mm/year. Spreading rates range from 20mm/year
to 165mm/year! The premises involed in the determination of spreading rates
are that
1. Rocks on the sediment volcanic contact have ages commensurate with the time
the rocks were at the ridge, and,
2. The distance of the area concerned from its' parent ridge is determinable.
By determining these two variables, the spreading rate can be ascertained!
Sea-Floor Subsidence
Oceanic crust forms hot! With time, three factors affect the rheostatics
of the ocreanic crust system. These are;
1. The rocks are forced away from the ridge by continued volcanic accretion
at the extensional boundary (the ridge)
2. The igneous rocks cool with time and become more dense.
3. The increased density of the rocks leads to isostatic re-equilibration (ie.
the crust subsides)
Because the younger, hotter, more buoyant rocks are always proximal to the ridge and the older, cooler denser rocks are distal to it, the age of the oceanic crust can be determined by empirical charts relating the depth of the crust to the depth at the relavent ridge system
There is a whole world of drilling and geophysical data for spreading and subsidence of the ocean floor! Some relevant examples can be downloaded here and interpreted by you! Pretty exciting stuff!!
We realise that not everyone has had experience with the intrinsic concepts of Marine Science. This 'computer' has numerous examples which will help you understand these fundamental facets! Very helpful, very colourful!