- Phacolith
A phacolith is a pluton parallel to the bedding plane or
foliation of folded country rock. More specifically, it is a typically lens-shaped pluton that occupies either the crest of ananticline or the trough of asyncline . In rare cases the body may extend as a sill from the crest of an anticline through the trough of an adjacent syncline, such that in cross section it has an "S" shape. In intensely folded terrain the hinge of folds would be areas of reduced pressure and thus potential sites formagma migration and emplacement.The term was coined and initially defined by Alfred Harker in his "The Natural History of Igneous Rocks" in 1909.
References
*Davis A. Young (2003) "Mind Over Magma: The Story of Igneous Petrology", page 335, Princeton University Press. ISBN 0-691-10279-1
*American Geological Institute. "Dictionary of Geological Terms". New York: Dolphin Books, 1962.
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