1. Batholith:
- Definition: A massive, irregularly shaped intrusion of igneous rock that covers at least 100 square kilometers. Batholiths are formed by the accumulation of multiple magma chambers over long periods.
- Formation: They are formed deep within the Earth's crust, often associated with mountain building and tectonic plate movement. As magma rises from the mantle, it cools and crystallizes, forming large masses of intrusive igneous rock.
- Characteristics: Batholiths are typically composed of granite and other felsic rocks. They can be exposed at the surface due to erosion of overlying rocks, forming spectacular mountain ranges.
- Examples: The Sierra Nevada Batholith in California and the Coast Mountains Batholith in British Columbia.
2. Dike:
- Definition: A tabular, sheet-like intrusion of igneous rock that cuts across existing rock layers.
- Formation: Dikes are formed when magma forces its way upward through cracks and fractures in the surrounding rock. The magma cools and crystallizes within the fissure, forming a wall-like structure.
- Characteristics: Dikes are typically composed of mafic or intermediate rocks, such as basalt or diorite. They can vary in width from a few centimeters to tens of meters.
- Examples: The Palisades Sill in New Jersey, which is actually a large dike, and the numerous dikes found within volcanic areas, such as Yellowstone National Park.
Key difference: Batholiths are large, massive intrusions that form over long periods, while dikes are smaller, sheet-like intrusions that form relatively quickly. Both are important features of Earth's geology and provide valuable insights into the processes that occur deep within the planet.
