Zoned Plagioclases in Layered Gabbros of the Skaergaard Intrusion, East Greenland

Abstract

A limited amount of careful optical work has been carried out on X three analysed felspars of gabbros belonging to the main layered series of the Skaergaard intrusion, east Greenland (Wager and Deer, 1939). The work was begun with the intention of providing precise optical data to be used in further defining the relationship between composition and optics. The primary precipitate felspar crystals, hitherto thought to be devoid of zoning, were found, however, to possess a zoning which prevents the data being used in this way.