Carbon cycle - name of theory related to volcanism?

Question

Ignore the organic reservoirs, and consider only the atmosphere,

carbonate and magmatic data for Earth. The carbon cycle on

Earth is a balanced transfer of carbon between reservoirs. One long-term aspect of the cycle is where carbon subducted in carbonate sediments is transferred back to the surface and the atmosphere during volcanism.

What is the theory that accounts for this transfer?

Answer 1

I think it goes something like this: -

When carbonate minerals and carbon itself are subducted to great depths there is a very considerable increase in temperature and the carbonates are converted to oxides plus CO2.

For example, calcium carbonate decomposes to CaO plus CO2 at 850 deg C at atmospheric pressure.



CaCO3  =>  <= Ca + CO2

This is actually an equilibrium reaction and an increase in temp drives it to the left. So at high pressures the the decomposition temp is much higher.

When vulcanism occurs large volumes of CO2 is often discharged into the atmosphere. The theory is that when lava reaches the earth's surface the huge reduction of pressure causes dissolved gasses and CO2 to come out of solution.