It sounds like you're asking about a terrane - a distinct block of rock that has a different geologic history than the surrounding area. Terranes are formed by the process of accretion, where they are transported and eventually "stuck" onto a larger landmass.

Here's why a terrane has a different geologic history:

* Origin: Terranes often originate far from their final resting place. They might have formed in a different tectonic setting, with different types of rocks and formations.

* Journey: As they move, they might be subjected to different geological events, including mountain building, erosion, and volcanic activity. These events leave their mark on the terrane, giving it a distinct geological character.

* Collision: When a terrane collides with a continent, it becomes "sutured" onto the edge of the existing landmass. This collision can cause significant geological changes in both the terrane and the continent.

Here are some examples of differences in geological history that can be seen in terranes:

* Rock Types: Terranes may contain different types of rocks than the surrounding area, such as metamorphic rocks formed under high pressure or volcanic rocks from ancient island arcs.

* Fossils: Fossils found in a terrane might be different from those found in the surrounding area, reflecting the different environments in which the rocks formed.

* Geological Structures: Terranes can have unique geological structures, such as folds, faults, and intrusions, that are not found in the surrounding area.

In summary: Terranes have a different geological history because they are formed in a different location and are subjected to different geological processes before becoming part of a larger landmass. Their distinct geological character makes them fascinating areas to study, offering insights into the Earth's dynamic history.