Anomaly 4B Pipe

This pipe contains highly magnesian olivine-phlogopite leucitites which throughout the entire pipe are present as an autolith breccia. The cores of the autoliths have zoned structures in which the central parts are formed of fine-grained olivine leucitite while the margins are of dark, very fine-grained rocks corresponding in composition to the same olivine leucitite. The autoliths are set in a matrix of either olivine leucitite of the same composition or of a lapilli or crystal tuff cement. There are abundant round and angular xenoliths of upper Jurassic leucite phonolite, which are not known from surface outcrop, as well as lower and upper Mesozoic alkali feldspar syenites.