Batholithe

A batholith, or batholithe in some languages, is a very large igneous intrusion that crystallized from magma cooling deep within the Earth's crust. By convention, batholiths cover an area greater than about 100 square kilometers (roughly 40 square miles) and can extend tens to hundreds of kilometers in length. They represent among the deepest and most extensive plutonic expressions of long-lived magmatic systems and often form the cores of mountain belts after uplift and erosion exposes them at the surface.

Formation and emplacement occur when magma intrudes the crust in multiple pulses, assembling a network of plutons that eventually coalesce into a single large body. The gas- and mineral-rich magma cools slowly, producing coarse-grained textures typical of plutonic rocks. Cooling times span millions of years, allowing substantial crystal growth.

Composition and texture are typically felsic, with granitic to granodioritic varieties being common. Batholiths may exhibit internal zoning and podlike or sheet-like internal structures. They are often associated with metamorphic and structural changes in surrounding rocks and can host ore deposits.

Notable examples include the Sierra Nevada Batholith in California, a classic composite batholith exposed along a long belt, and the Coast Range Batholith of western North America. Other well-known batholiths occur in the Italian Alps (for example, the Adamello Batholith) and in various continental-margin settings around the world.

Geologically, batholiths record episodes of crustal growth and prolonged magmatic activity associated with subduction and continental collision, contributing to the formation and evolution of continents.