Image of the Week: Jan. 2 - 8, 2005

Dike

This igneous dike cuts the Laurel Hill pluton
southwest of Mount Hood, Oregon.

Note the pattern of joints formed as the magma cooled, essentially perpendicular to the walls of the relatively narrow dike.

Dikes are tabular bodies of intrusive igneous rock that form as molten rock forces its way into a fracture and eventually cool.
Dikes cut across the structure of layered or foliated rocks, or cut through massive rocks (such as granite).

The rock into which this dike is intruded is part of the Laurel Hill pluton, a granitoid stock (~15 km²) about 11.5 Ma, part of the Western Cascades.

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