Lopolith

Saturday, June 19, 2010

A lopolith is a large igneous intrusion which is lenticular in shape with a depressed central region. In other words, it is a mass of igneous rock similar to a laccolith but concave downward rather than upward. 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 during the early 1900s in describing the Duluth gabbro complex in northern Minnesota and adjacent Ontario.

Lopoliths typically consist of large layered intrusions that range in age from Archean to Eocene. Examples include the Duluth gabbro, the Sudbury Igneous Complex of Ontario, the Bushveld igneous complex of South Africa, the Skaergaard complex of Greenland and the Humboldt lopolith of Nevada. The Sudbury and Bushveld occurrences have been attributed to impact events and associated crustal melting.