The excursion will visit the Skaergaard intrusion and...

The excursion will visit the Skaergaard intrusion and surrounding areas on east Greenland (fig. 1). This area has had a profound influence on the development of modern igneous petrology and has served as a type locality for detailed petrological and geochemical studies since the publication of the classical description by Wager and Deer (1939). Many features of layered intrusions are magnificently exposed for study in the clean, glacially polished outcrops. The intrusion hosts a potentially economic stratigraphic zone of gold and palladium which was discovered in 1987 (the Platinova reefs). The notation used in the following description follows our recent paper on Skaergaard geology (Irvine et al. 1998).

The Skaergaard intrusion is situated on the east coast of Greenland near the mouth of the large Kangerdlugssuaq fjord between the towns of Ammassalik and Ittoqqortoormiit (Scoresby Sund) (fig. 2). The intrusion formed around 55 Ma ago as a part of the Tertiary North Atlantic magmatic province. This province is currently one of the most promising targets for platinum-group element research in Europe. Elevated platinum-group element concentrations have been repored from several intrusions on East Greenland (Bird et al. 1991, 1995; Arnason and Bird 1994, Nielsen and Brooks 1995, Arnason et al. 1997, Andersen et.al. 1998) and the Inner Hebrides in Scotland (Butcher et al. 1999, Pirrie et al. 2000, Power et al. 2000).

The Skaergaard intrusion (fig. 3) is divided into three main suites of rocks having parallel evolution trends in mineral assemblages and compositions: The Layered Series (LS), which consists of material accumulated on the floor of the magma chamber, the Marginal Border Series (MBS), which consists of material that crystallized on its walls, and the Upper Border Series (UBS), which consists of material that crystallized and/or accumulated under its roof (fig. 4). The LS Lower Zone (LZ) subunits a and b are very well exposed on Uttental Plateau, the LZ subunit c and the Middle Zone (MZ) on Kraemer Island, and the Upper Zone (UZ) in the plateau to the west of Basistoppen. The MBS is exposed along the western margin of the intrusion and can be easily examined at different stratigraphic heights. The UBS occurs mostly in mountainous terrain but can be examined along the eastern shore of Skaergaardsbugt.

Figure 1: The Skaergaard intrusion is situated on the east coast of Greenland, where it is associated with a large continental flood basalt province. The intrusion formed around 55 Ma ago during the Tertiary opening of the North Atlantic ocean.

Fig. 2: The Skaergaard intrusion is situated at the unconformity that forms the base of a more than 8 km thick succession of Tertiary plateau basalts (brown). The basalts overlie a succession of Cretaceous-Palaeocene sediments (yellow), which directly overlie the Precambrian basement complex (orange). The Skaergaard intrusion is one of a suite of gabbroic and ultramafic intrusions (blue dots) exposed along the coast.

Fig. 3: Geology of the Skaergaard Intrusion. The intrusion occurs at an unconformity between the Precambrian basement (pink), a succession of Cretaceous-Palaeocene sediments (light yellow) and the Tertiary (Palaeocene-Eocene) flood basalts (light grey). The Skaergaard intrusion is divided into three series, the Marginal Border and Upper Border Series (MBS and UBS, green) and the Layered Series (shades of blue). The Layered Series is further subdivided according to mineralogical changes into Lower (LZ), Middle (MZ), and Upper (UZ) zones. The intrusion is cut by a later layered intrusions, the Basistoppen sill and Vandfaldsdalen macrodike (both dark grey). The MZ hosts a zone rich in gold and palladium, the Platinova reefs (dark yellow).

Fig. 4. Diagram of the major lithological units and geological processes we envisiage have taken place during the crystallisation of the Skaergaard intrusion. The figure shows a compilation of structures that are exposed in the field and their likely ways of formation. The diagram displays a time-lapsed image of our interpretation of the the dynamic environment of crystallisation during the formation of the lower part of the MZ.