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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