Question

What is the largest intrusive igneous rock body? A) dike C) sill B) volcanic neck D) batholith

Short answer

The largest intrusive igneous rock body is a batholith.

Step-by-step solution

Understand the Terms

Each option given is a type of intrusive igneous rock formation. - **Dike**: A vertical or steeply inclined sheet of rock that cuts through layers of rock. - **Sill**: A horizontal sheet of rock that forms between layers of rock. - **Volcanic Neck**: The solidified magma within a volcano's conduit. - **Batholith**: A vast mass of intrusive igneous rock that has solidified deep within the Earth's crust.

Identify Characteristics of a Batholith

A batholith is the largest type of intrusive igneous rock body. It is a massive, irregularly shaped body that covers at least 100 square kilometers when exposed at the surface. Batholiths form when many plutons converge to form a vast body beneath the Earth's surface.

Comparison with Other Options

- **Dike** and **Sill** are smaller, sheet-like structures and do not cover vast areas. - **Volcanic Neck** represents a smaller, focused intrusion on the scale of a single volcano. - **Batholiths**, in contrast, are larger bodies that can span hundreds of kilometers in width, thus making them the largest type of intrusive igneous rock body.

Conclusion

By evaluating the characteristics and relative sizes of each rock formation option, we determine that the batholith is the largest intrusive igneous rock body among the given choices.

Key concepts

batholith

Batholiths are fascinating geological formations, known as the largest bodies of intrusive igneous rock. They form deep within the Earth's crust and often cover extensive areas, at least 100 square kilometers, when exposed on the surface. These vast rock masses are created when multiple plutons—large bodies of magma—merge together.
As these plutons cool and solidify over millions of years, they form the massive batholith. They are usually composed of granitic rock, which is light-colored and rich in quartz and feldspar. Because of their immense size and composition, batholiths commonly form the core of mountain ranges, like the Sierra Nevada in the United States.

• Largest intrusive igneous rock formation.
• Cover areas of at least 100 square kilometers.
• Form the central cores of many mountain ranges.

Understanding batholiths gives insight into the dynamic processes beneath the Earth's surface, highlighting how internal forces shape our planet's landscape.

dike

Dikes are intriguing formations representing a different style of intrusive igneous rock. Unlike batholiths, dikes are much smaller and tend to form vertical or steeply inclined sheets of rock. These sheets cut through pre-existing rock layers, creating pathways for magma to move. They form when magma intrudes into cracks in a host rock, where it then cools and solidifies into narrow bands.
Dikes can range in size from just a few centimeters wide to several meters, but they typically don’t cover large surface areas like a batholith. They play a vital role in the geology of an area because they provide evidence of past volcanic activity and contribute to the formation of new landforms.

• Vertical or steeply inclined sheets of rock.
• Form by cutting across existing rock layers.
• Indicators of ancient volcanic activity.

By studying dikes, geologists can trace the history of magma movement and understand the geological stress conditions of an area.

sill

Sills are another type of intrusive igneous rock formation, distinct from both dikes and batholiths. They form as horizontal sheets that intrude between pre-existing layers of rock. Sills are created when magma fills the space between these layers and solidifies. Over time, this process results in evenly layered rock formations that adjoin horizontally.
While sills can vary in terms of length and thickness, they often remain more uniform due to their horizontal orientation. They differ from dikes, which cut across the bedrock, and may be substantially smaller than batholiths.

• Horizontal sheet-like formations.
• Formed between existing rock layers.
• Typically more uniform in thickness.

Studying sills helps geologists understand the conditions under which magma intrudes and how pressure variations affect the orientation of magma within the Earth's crust.

volcanic neck

Volcanic necks are extraordinary formations, representing what remains of an extinct volcano. They form when magma, which once fed a volcano, solidifies within the conduit, the volcanic pipe connecting the magma chamber to the surface. Over time, erosion removes the surrounding volcanic material, leaving behind the harder, more resistant rock of the conduit as a striking landform.
A volcanic neck is much smaller in scale compared to batholiths or other large igneous bodies, and it often forms a prominent, tower-like structure. Some famous volcanic necks include Devil's Tower in Wyoming, USA, which offers breathtaking views and serves as a natural monument.

• Formed by solidified magma within a volcano's conduit.
• Exposed after surrounding rock has eroded away.
• Creates dramatic, isolated structures in the landscape.

Volcanic necks provide valuable information about volcanic activity and erosion processes, showcasing how the Earth's surface evolves over millions of years.