laccolith


laccolith
laccolithic, laccolitic /lak'euh lit"ik/, adj.
/lak"euh lith/, n. Geol.
a mass of igneous rock formed from magma that did not find its way to the surface but spread laterally into a lenticular body, forcing overlying strata to bulge upward.
Also, laccolite /lak"euh luyt'/.
[1875-80; < Gk lákko(s) pond + -LITH]

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      in geology, any of a type of igneous intrusion that has split apart two strata, resulting in a domelike structure; the floor of the structure is usually horizontal. A laccolith is often smaller than a stock, which is another type of igneous intrusion, and usually is less than 16 km (10 miles) in diameter; the thickness of laccoliths ranges from hundreds of metres to a few thousand metres. They can be contrasted with sills (sill), which are sheetlike intrusions oriented parallel to the bedding of the enclosing rock: a laccolith's ratio of diameter to thickness should be less than 10; a larger ratio would make the body a sill. Acidic rocks are more common than basic rocks in laccoliths. Although the lower portions of laccoliths are seldom visible, they usually are interpreted as having a relatively small feeder from a magma source below. A well-known example of a laccolith is found in the Henry Mountains, Utah.

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