Intrusioihin

Intrusioihin is a term used in Finnish geology to describe magmatic intrusions—bodies of igneous rock that crystallize from magma that has forced its way into preexisting rock near or below the Earth's surface. The word appears in technical texts to refer to multiple intrusion events or bodies and is used when discussing the collective occurrence of intrusions in a region.

In geological classification, intrusions are grouped by geometry and size. Dikes are tabular bodies that cut across surrounding rocks. Sills intrude parallel to layering within the rock. Plutons are large, irregular bodies that crystallize at substantial depths, often forming coarse-grained rocks such as granite. Laccoliths, another form, create uplifted caps as the intrusion domes the overlying rocks. The variety of intrusion styles records differences in magma viscosity, pressure, and tectonic setting.

Formation and textures arise from cooling histories. Magma that cools slowly at depth tends to form coarse-grained rocks, while faster cooling near the surface produces finer textures. The margins of intrusions commonly cause contact metamorphism, producing secondary minerals in the surrounding rocks. Intrusions can also influence local mineralization, with certain ore deposits forming in association with intrusive bodies or their contact zones.

Significance in geology lies in revealing tectonic and magmatic evolution, crustal composition, and thermal histories of regions. Intrusive rocks are key for isotopic dating, petrology, and exploration geology, helping to reconstruct the geodynamic history of their host areas.