Apr 28 2014
Plutonic rocks are igneous rocks that are present at great depths of the earth. In other words they are intrusive igneous rocks. Plutonic rocks are formed when magma solidifies under the earth’s surface. Plutonic rocks are named after Pluto, the classical god of the underworld.
Gabbro, diorite, and granite are some examples of plutonic rock. An intrusive or plutonic environment is found under the earth’s surface. At these depths, the temperatures are high and the magma cools down slowly.
Types of Plutonic Rocks
Plutonic rocks are classified as tabular and massive.
Tabular Plutonic Rocks
These plutons are formed when magma is forced into a fissure or crack in between sedimentary rock beds. They get the name tabular due to their sheet-like or table-like shape. Tabular plutons are further classified into sills, laccoliths, and dikes, based on the differences in shape.
- Sills – These are parallel to the sedimentary beds and are formed from magma that has forced its way in. They are also referred to as concordant tabular plutons
- Laccoliths – Similar to sills, but have an upward bulge in the form of blisters. These bulges may sometimes be as big as mountains
- Dikes – These rocks are formed from magma that is forced into cracks, and are vertically aligned like a wall.
Massive Plutonic Rock
Massive plutons are massive blobs of igneous rocks. They have similar dimensions to that of tabular rocks. Massive plutons are classified into stocks and batholiths.
- Stocks – These are massive plutons that are formed from magmatic chambers. They are huge in size like mountains. A single magma chamber may have fed one or more volcanoes
- Batholiths – They are much larger in size when compared to stocks. They are formed from several different magma chambers that are placed under a volcanic range over a period of time.
Sources and Further Reading