Chapter 9, Problem 1RQ

To determine

The changes that a rock undergo during the formation of an orogenic belt such as the Alps.

Answer to Problem 1RQ

The rocks at orogenic belt such as Alps undergo thrust faulting followed by the metamorphism, passive flow folding and eventual upliftment giving rise to the mountain belt.

Explanation of Solution

The Alps, is a result of collision tectonics. Here, the continental plate boundaries collide with each other resulting in the orogeny. There occurs a large number of thrust faults in which the edge of one block slips up and over the margin of the other. This boundary with separate blocks is known as a suture.

During the thrusting process at or near the suture, the rocks of footwall, goes tens of kilometers deep into the earth but, as they are less dense than the mantle, they gradually stop moving down. These rocks undergo high grade of metamorphism and initiates passive flow folds and tectonic foliation. At the same time, blocks of hanging wall goes several kilometers upwards. Due to folds and reverse faults, the rocks that are metamorphosed at the depth of Orogen are eventually brought up to the earth’s surface. The crust here is around 70km in thickness.