How to Determine the Relative Age of Granite and Sandstone Layers

What is the relationship between granite and sandstone layers?

A mass of granite is in contact with a layer of sandstone. Using a principle described in this chapter, explain how you might determine whether the sandstone was deposited on top of the granite or whether the magma that formed the granite was intruded after the sandstone was deposited.

Answer:

Granite in crustal rock and are felis rocks that are found near to the surface.

The granite is a coarse-grained intrusive igneous rock and are commonly white, pink and grey and is massively hard and rough. More commonly found in the continental crust, while sandstone is mainly sand-sized rock fragments and is resistant to weathering. Sandstones are a result of the deposition of layers of sand grains on top of the granite.

Using the principle of 'cross-cutting relationships', we can ascertain that if the granite cuts through the sandstone, it was formed after the sandstone's deposition. However, if the granite does not intrude into the sandstone, it infers that the sandstone layer was deposited after the granite was formed.

The principle of cross-cutting relationships in geology can assist us in determining whether the sandstone was deposited on top of the granite or vice versa. This principle states that an igneous intrusion, such as granite, is always younger than the rock types it intrudes into. Hence, if the granite shows signs of cutting through the sandstone, it would indicate that the magma, which formed the granite, intruded after the sandstone layer was deposited.

However, if the sandstone sits on top of the granite without any signs of intrusion, then it indicates that the sandstone was deposited after the granite was formed.