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extensional settings, signi
cant depletions of Nb and Ta relative to Th and La, low
TiO
2
contents (0.92
2.17 %), low ratios of Rb/Cs, K/Rb and Ce/Pb as well as high
ratios of Ba/La and Ba/Th suggest close genetic relationships to subduction-related
processes. Whereas Sr and Nd isotope ratios show relatively large variations (Sr
87
/
Sr
86
= 0.7078
-
0.7105, Nd
143
/Nd
144
= 0.51242
0.51215), Pb isotope ratios display
a very restricted range with Pb
206
/Pb
204
= 18.68
-
-
18.88 and variable. The observed
petrographic, geochemical and isotopic characteristics are best explained by a
genetic model involving preferential melting of phlogopite-rich veins in an origi-
nally depleted lithospheric mantle source, whereby the metasomatic enrichment of
the mantle source is tentatively related to the addition of components from sub-
ducted sediments during consumption of Tethyan oceanic lithosphere.
-
4.9 Lamproitic Rocks from Greenland
4.9.1 Batbjerg Complex
The complex (Fig.
4.28
) is located 15 km beyond the head of Kangerdlugssuaq
Fjord (Gittins et al. 1982). The complex is 7 km long with an elevation of 1 km and
is exposed along the eastern side of the Kangerdlugssuaq glacier. It intrudes Pre-
cambrian gneiss, marble and quartzite. These metasediments are thermally and
metasometically altered, and includes Na-rich melilite, pectolite, wollastonite and
ulvospinel. The main complex is composed of pyroxenite and jacupirangite with
minor amounts of ijolite and urtite; which are intruded by syenite, quartz syenite
and granite. According to Gittins et al. pyroxenes are present as a predominant
homogeneous mineral, but sometimes zoned forming acmitic rims. The other
phases present in the pyroxenites are phlogopite (sometimes biotite), olivine and
amphibole. The salic minerals include leucite, nepheline, K-feldspar and pseudo-
leucite with intergrowth of nepheline and K-feldspar. In many pyroxenites, patchy
intergrowth of nepheline and kalsilite are also observed. When such intergrowths
are observed, leucite is usually found to be absent. Discrete grains of pyroxene are
rare and fresh leucite crystals are found as an interstitial mineral. The pyroxenite
body is intruded by coarse-grained phlogopite peridotite dykes. The phlogopites
show reverse pleochroism, and olivines are sometimes up to 1 m across.
4.9.2 Holtsteinberg Lamproit from Greenland
Scott (1980) made detailed investigation of kimberlite and lamproite dykes of
Holtsteinberg, located in the central part of west Greenland (Fig.
4.29
). The
majority of the dykes occur in the coastal area between Holdsteinberg and Itivleq
but a few area found north of Sukkertoppen, Iskappe (Fig.
4.29
).
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