Big Bend National Park

Metamorphic Processes

Metamorphic rock is a type of rock that forms as a result of an existing rock remelting as the result of extreme heat or pressure. Often metamorphic rocks retain some characteristics of the parent rock from which it is derived. There are two types of metamorphosis that rocks can undergo, contact metamorphosis and regional metamorphosis.

Regional metamorphosis occurs when large pockets of molten rock rise to up in the crust, in a similar manner that hot air rises. As a result, the rocks that lies over this hot pocket of magma is partially melted and transformed in a wide geographic area.

Contact metamorphosis occurs much in the same way. However, the molten pocket of magma transforms the overlying rock only in places where the magma is actually touching.

Big Bend's active igneous history of intrusions and volcanic activity did create some metamorphic rocks. However, there is only one place in the park today which has exposed metamorphic rock. Most of the other areas where metamorphosis had occurred have long since eroded and have been washed away.

Dominguez Mountain is the only area in the park where metamorphic rock is exposed. It is located in south central portion of the park. To the left is a portion of the US Geological Survey map of the Big Bend area. Due to its distance from the park roads and geographical obstacles, we were unable to get any photographs. The pink portion of the map shows an igneous intrusion that happened during the mountain building episodes in the park. The stippled grey portion of the map shows the country rock which was metamorphosed. Before the intrusion, this rock was mainly composed of tuff with interbedded bentonite clays.