A lopolith is a large
igneous intrusion which is
lenticular
Lenticular is an adjective often relating to lenses. It may refer to:
* A term used with two meanings in botany: see
* Lenticular cloud, a lens-shaped cloud
* Lenticular galaxy, a lens-shaped galaxy
* Lenticular (geology), adjective describing a ...
in shape with a depressed central region. Lopoliths are generally concordant with the intruded
strata with
dike or funnel-shaped feeder bodies below the body. The term was first defined and used by
Frank Fitch Grout
Frank or Franks may refer to:
People
* Frank (given name)
* Frank (surname)
* Franks (surname)
* Franks, a medieval Germanic people
* Frank, a term in the Muslim world for all western Europeans, particularly during the Crusades - see Farang
Cur ...
during the early 1900s in describing the
Duluth gabbro complex in northern
Minnesota and adjacent
Ontario.
Lopoliths typically consist of large
layered intrusion
A layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions can be many kilometres in area covering from around to over and several hundred metres to ...
s that range in age from
Archean
The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archea ...
to
Eocene. Examples include the
Duluth gabbro, the
Sudbury igneous complex The Sudbury Igneous Complex is a 1,844 million year-old impact melt sheet in Greater Sudbury, Northern Ontario, Canada. It is part of the Sudbury Basin impact structure, and is classified as a lopolith
A lopolith is a large igneous intrusion whi ...
of Ontario, the
Bushveld igneous complex
The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is ...
of
South Africa, the
Great Dyke in
Zimbabwe, the
Skaergaard complex
The Skaergaard intrusion is a layered igneous intrusion in the Kangerlussuaq area, East Greenland. It comprises various rock types including gabbro, ferro diorite, anorthosite and granophyre.
Discovered by Lawrence Wager
in 1931 during the Br ...
of Greenland and the Humboldt lopolith of
Nevada. The Sudbury occurrence has been attributed to an
impact event and associated crustal melting.
See also
*
Laccolith
A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma (molten rock) rising through the Earth's crust begins to spread out horizontally, prying apar ...
*
Phacolith
A phacolith is a pluton of igneous rock 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 an anticline or the trough of a syncline. In rare ...
*
Batholith
A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...
References
*Blatt, Harvey and Robert J. Tracy, 1996, ''Petrology: Igneous, Sedimentary and Metamorphic'', 2nd ed., pp. 15-16, Freeman,
*Guilbert, John M., and Park, Charles F., Jr. (1986) ''The Geology of Ore Deposits'', Freeman,
Igneous rocks
Petrology
Igneous intrusions
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