What defines the term laccolith?

A laccolith is defined as an intrusive igneous rock body that has formed when magma intrudes into sedimentary rock layers and spreads laterally beneath the surface, creating a dome-like structure. The significant characteristic of a laccolith is that it is not flat but instead has a lesser thickness compared to its lateral extent, which often leads to the formation of uplifted geological structures above it.

This formation occurs when the pressure of the magma is sufficient to cause the overlying rock layers to bulge upward without breaking through to the surface, distinguishing it from other types of intrusions. The lateral spreading and the upward dome-like shape are critical points in understanding what a laccolith is and how it differs from other intrusive rock formations.

In contrast, other definitions provided do not capture these defining features. For example, a volcanic neck refers to the solidified core of a volcanic pipe, while a flat, tabular body would describe a different form of intrusion, such as a sill. A small granite pluton generally refers to a less expansive body of granite that may not share the distinctive characteristics of spreading and dome-like shapes associated with laccoliths.