Chapter 8, Problem 1GST

To determine

The sequence of formation of features present in the accompanying image that shows metamorphic rock gneiss, a basaltic dike, and a fault with logic.

Answer to Problem 1GST

The sequence of formation of features present in the image from older to younger is Gneiss, dike, and fault. Gneiss must have formed before the intrusive dike, in order for it to cut through gniess. As the fault offsets the dike, the fault occurred after the intrusion of dike. This is an application of the principle of cross-cutting relationships.

Explanation of Solution

“Principle of cross-cutting relationships states that the geological feature which cuts across strata is always younger than the one it cuts through it” A fault is a break or fracture in the rock, along which the displacement occurs.

According to the principle of cross-cutting relationship, the igneous dike is younger and formed after the metamorphic rock Gneiss that cuts through it. Gneiss is a high grade foliated metamorphic rock and must have formed before the dike otherwise the dike would have been metamorphosed too. The fault has split and separated the dike. and hence, the igneous dike must have formed before the fault occurred.