Genesis of the Fiskenaesset Anorthosite Complex
The 2.9 billion year old Fiskenaesset Anorthosite Complex is made up of a layered series of anorthosites and gabbros that occur as dissected layers and lenses within the Tasiusarsuaq terrane of southwest Greenland. The contact zone at Fiskenaesset Harbor displays a wide variety of unusual lithologies containing sapphirine, kornerupine, ruby corundum, hšgbomite, clintonite, tourmaline, geikielite, ilmenite, enstatite, spinel, gedrite, cordierite, biotite, hornblende, and plagioclase. These Al- and Mg-rich assemblages are confined to a thin zone between the anorthosite and overlying rocks.
Oxygen and hydrogen isotope ratios indicate that unusual rocks at the upper contact of the Fiskenaesset Anorthosite are the products of hydrothermal alteration by seawater at the time of anorthosite intrusion. Subsequent granulite-facies metamorphism of these Ca-poor and Al- and Mg-rich rocks produced sapphirine- and kornerupine-bearing assemblages. Because large amounts of surface waters cannot penetrate to depths of 30 km during granulite facies metamorphism, the isotopic signature of the contact rocks must have been obtained prior to regional metamorphism. The stable isotope and geochemical characteristics of the contact rocks support a model of shallow emplacement into Archean ocean crust for the Anorthosite.
Peck, WH, and Valley, JW, 1996, The Fiskenaesset anorthosite complex: Stable isotope evidence for shallow emplacement into Archean ocean crust: Geology, v.24, p. 523-526.