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1.2 GPa, then the difference in the liquidus relationship between the two sets of
study can be explained. The Gauss-berg lamproites were studied in presence of
excess water. Experimental studies on orendites (Barton and Hamilton 1982) on the
other hand were conducted in H
2
O-de
cient condition. Foley (1990) considered
that in presence of intermediate H
2
O contents the liquidus temperatures should be
comparable. He thought that if more H
2
O was added in the orendite system, there
should have been expansion of the phlogopite
field towards the liquidus, due to
depression in the liquidus temperature and increase in the phlogopite phase. This
would not allow olivine to be stable at higher pressure in the H
2
O-rich system. In
such a case there should be a four-phase
field of mica + olivine + orthopyrox-
ene + liquid in the liquidus of the orendite at a pressure of less than 2.7 GPa. Berton
and Hamilton (1982) doubted that orendite with 55 wt% SiO
2
could be derived
from a lherzolite source, but suggested that olivine orendites, which are olivine-
normative, despite having 53 wt% SiO
2
(Kuehner et al. 1981), might have origi-
nated by melting of a mica and garnet-bearing lherzolite at a pressure of about
2.7 GPa. According to Foley (1990), the effect of water on the phase relation should
expand the phase volume of olivine and mica; and garent should appear at much
higher pressure (Fig.
13.8
a). The assemblage olivine + mica + orthopyrox-
ene + liquid could be near liquidus phases in the pressure range of 1
2 GPa.
According to Foley, the two sets of experiments are compatible with a mica
harzburgite or mica lherzolite source, which is free from garnet. Foley (1990)
studied an olivine lamproite from West Kimberley in presence of a
-
uid
(H
2
O>>CH
4
). This study showed the presence of following liquidus phases:
olivine at lower pressure, phlogopite under intermediate pressure and orthopyrox-
ene at higher pressure.
Liquidus experiments on an olivine lamproite (Fig.
13.8
c) has been performed at
pressures between 4.5 and 5.5 GPa in the presence of a reduced
fluid (with
H
2
O>CH
4
) (Foley 1990). Results show that olivine is the liquidus phase up to a
pressure in excess of 5.0 GPa, above which olivine, orthopyroxene, and phlogopite
occur together at the liquidus. The results are consistent with the hypothesis that a
range of primary magmas from leucite lamproite to olivine lamproite can be derived
by partial melting of phlogopite harzburgite as a function of pressure between <1.5
and >6 GPa under reducing conditions. Simple interpretation of the results in terms
of a homogeneous phlogopite harzburgite, however, belies, a complex melting
process. The phase relations are also consistent with melting of a veined source rock
in which neither vein nor wall-rock consists of phlogopite harzburgite.
13.2.6 Phase Equilibria Studies on (Lamproites
from Damodar Valley, India
Experimental study was made by Gupta et al. (2002) on powdered samples of three
lamproites from Gondwana basins occurring in the Damodar valley region of east
India. Whereas one of the lamproites is from the Jarangdih mine of Bokaro basin,
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