How do intrusive igneous bodies form?

Eg - Batholiths, Sills, Dykes...all that good stuff.


Any answers would be greatly appreciated|||rocks melt when the pressure lowers enough or temperature rises enough, or chemistry changes enough to move the material from the stability zone for solid to the stability zone of liquid.





This melting may occur in minor amounts or in huge amounts. Once melted, liquid rock tends to rise up toward the surface of the earth. How this occurs depends on the overlying rock and how much buoyancy pressure the liquid places on the solid stuff up above.





Batholiths occur where there is a huge amount of rock melt. Dikes and sills are simply offshoots of the main mass of liquid that manages to find its way into the surrounding solid rock through weak zones, like fractures and faults.





basically, the big blob of liquid down below tries to rise if it can. Sometimes alot of it finds its way through the surrounding rock, but generally a huge mass gets stuck in one place and cannot get out very easily, except in little offshoots (dikes and sills). Sometimes the liquid doesn't only squeeze its way into cracks and weak zones, but actually melts its way.