The Upper Border Series


The Upper Border Series is exposed towards the south-east of the intrusion. It occurs mostly in an area with inaccessible mountainous terrain, but a few exposures can be examined along the shore of Skaergaardsbugt. The UBS is divided into zones that are equivalent to the divisions of the LS in terms of cumulus mineralogy. The uppermost unit, the UBSt is equivalent to the tranquil division of the MBS, the UBSa to the LZ, UBSb to the MZ, and the UBSg to the UZ of the LS. The UBS is mostly eroded away but still displays a stratigraphic succession of some 960 m (Naslund, 1984). The abundant blocks in the LS derived from the UBS demonstrate that it was periodically scaled away during crystallisation, the stoping locally even breaking the original roof of the intrusion. The diversity of included blocks in the LS indicate that the UBS was more diverse than the exposures suggest, notably by having extensive units of anorthosite (possibly flotation cumulates). Large unconformities and irregularities in the exposed stratigraphic succession are consistent with the abundant blocks in the LZ and MZ, and it is difficult to guess how extensive the units have been over the central parts of the intrusion. The exposed parts of the UBS is the most intensely hydrothermally altered unit of the intrusion and is transgressed by two major later intrusions (the Basistoppen sheet and the Tinden granophyre sill) and numerous mafic dikes constituting locally up to 15% of the outcrop (Naslund, 1984).

Layering in the UBS appears to be well developed although less systematic than in the LS (Naslund, 1980). Both modal and textural layering has been documented from the exposures (Naslund, 1980) and from the included blocks in the LS (Irvine et al., 1998).
 7.1 Subdivision and stratigraphic relations
 7.2 Layering and related features

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