Basaltdike

Basaltdike (basalt dike) is a tabular igneous intrusion that cuts across preexisting rock units. It forms when basaltic magma exploits fractures or weaknesses in the surrounding rock and crystallizes as basalt. Dikes are generally vertical or steeply inclined, though their orientation can vary, especially in dike swarms associated with tectonic extension.

Texture and composition: Because cooling occurs at the margins where the dike contacts the country rock, basaltdikes typically have chilled, fine-grained margins and a relatively fine-grained interior. They are mafic, rich in plagioclase and pyroxene, with possible olivine. Depending on cooling rates and internal zoning, the interior may be uniform in texture or show crystals set in a finer groundmass.

Geologic significance: Basaltdikes document magmatic activity and the pathways by which magma moved through crust. Dike swarms help map ancient crustal structures and stress fields during intrusion. Radiometric dating of dikes provides timing for magmatic events such as rifting or large igneous province activity. While dikes can host mineralization along contacts, the dikes themselves are typically not primary ore bodies.

Relations to other intrusions: Dikes differ from sills in orientation relative to host rock layering; dikes cut across layers, whereas sills intrude parallel to layering. The term basalt dike is often used interchangeably with diabase dike in regions where the dike is coarser-grained, though basalt generally denotes finer-grained varieties.

Distribution: Basaltdikes occur in many volcanic and extensional settings worldwide, including large igneous provinces and continental rift zones. Notable examples include dike swarms within the Deccan Traps and Karoo Basalt provinces, and basaltic dikes in Icelandic rift zones.