Magmas cool exothermically, releasing heat into the host rock or atmosphere . Magmas are open systems, which allows for the transfer of material, dissolved gases and fluids with the surroundings. Cooling is influenced by the environment. The composition of the magma affects the crystallization temperature. With increasing pressure the temperature of crystallization decreases.
Granitic plutons crystallize at approx.
Rates of Ascent and Cooling These are related to the structure and physical characteristics of the magma body, e.g. size, shape, viscosity, composition, etc. A medium to large batholith with a volume of 10,000 km 3 may require up to 10 million years to completely cool.