An intrusion is always younger than the rock layers around and beneath it. More clues come from the study of faults. A fault is a break in Earth’s crust. A fault is always younger than the rock it cuts through.
Are Batholiths older than dikes?
Dike A also crosscuts the sandstone layer so the dike is younger. … Dike A does not cut the batholith so other relationships must be used. Dike B clearly cuts the batholith; the sill fed by dike B is crosscut by dike A, proving that dike A is younger than dike B and younger than the batholith.
How is dike formed?
Dikes are tabular or sheet-like bodies of magma that cut through and across the layering of adjacent rocks. They form when magma rises into an existing fracture, or creates a new crack by forcing its way through existing rock, and then solidifies.