Devereaux Beach, Marblehead

In the pictures above (the right one is a close up of the one on the left), you can see rocks of two distinct colors. The dark rock is Salem Gabbro, and the light rock is the Quincy Granite. What are some different ways that this outcrop could have been formed?

These three pictures (above and to the right) show the same two types of rock as the pictures at the top. In this case, you can see the dark rock is actually trapped inside the lighter rock. This is called a xenolith. By studying these photos, can you tell which rock is older? What is your evidence?



This picture shows a basalt dike cutting through the rock formation. How is this process different from the one that formed the xenoliths visible above?