Ocean 540
Winter 2001
Problem Set #1

Due Wednesday, January 17, 2001

1. As a simple model for isostatic equilibrium of the earth, with compensation within the mantle, consider a continental block of thickness T in relationship to an ocean of depth 4 km and an oceanic crust 6 km thick. Derive an expression for the elevation of the continent above sea level as a function of T. For densities assume continent 2700 kg m^-3, ocean 1000 kg m^-3, oceanic crust 3000 kg m^-3, and mantle 3300 kg m^-3. What is the minimum thicness of the continental block for it to stand above sea level?
2. If the average spreading rate of the mid-ocean ridge system were to increase by 50%, estimate the size of the change in sea level that would result. Assume a symmetric ocean basin (ridge in center, subduction at both sides) of width 12000 km. Comment on any other assumptions that you make and assess their validity.
3. Suppose that at the end of the last glacial period, the temperature of the deep northern Atlantic Ocean abruptly increased 1°C. introducing a thermal perturbation in the underlying sediments. How much time would need to pass before a reliable conductive heat flow measurement could again be made? What criteria have you adopted for the term reliable? (Hint: It is useful to work at the limit of no pre-existing heat flow.)
4. Consider the binary system Di-An. Draw plots of the relationships of the composition of the liquid, the composition of the residual solid and the temperature as a function of the fraction of liquid for a closed, equilibrium system of bulk composition An₂₅. Phase Diagram for System Di-An.