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silicic and probably less calcic and less alkaline than liquids with higher CO
2
contents in equilibrium with the same assemblage (Green 1973).
Garnet did not appear as the near-liquidus phase at 3.0 GPa in the biotite
mafurite composition. This mineral, however, was found in the melting interval of
another highly potassic olivine leucitite (Cundari and O
Hara 1976) at pressures
above 3.0 GPa and therefore, the above conclusions should be also qualitatively
valid for the melting of an assemblage containing, phlogopite + olivine + orthopy-
roxene + clinopyroxene + garnet, at pressures higher than 3.0 GPa.
'
13.2.9 Phase Relations in an Olivine Ugandite under High
P
T Conditions
-
An olivine ugandite from South West Uganda was studied at pressures between 1.0
and 4.0 GPa under volatile-present conditions with 5, 15, 25 and 40 wt% added
H
2
O under an oxygen fugacity, which is slightly greater than the NNO buffer
condition. The same lamproite was studied by Edgar et al. (1984) in presence of
volatiles H
2
O
½
þ
CO
2
;
ð
Þ
¼
:
under similar oxygen fugacity condition.
Results of their experiments in presence of variable H
2
O contents are shown in
Fig.
13.17
a
XCO
2
0
75
c, whereas run products related to their experiments in presence of
-
½
are summarized in Fig.
13.18
. Figure
13.17
a
displays change in the slope of the liquidi as a function of pressure in presence of
ð
H
2
O
þ
CO
2
;
XCO
2
ð
Þ
¼
0
:
75
Þ
(a)
(b)
(c)
4.0
4.0
(Water
Saturated)
5% H
2
O
4.0
15% H
2
O
15%
H
2
O
5%
H
2
O
3.0
3.0
Dry
3.0
2.0
2.0
2.0
1.0
1.0
1.0
1100
1300
1500
1100
1300
1500
1000
1200
1400
T
o
T
o
T
o
Fig. 13.17 a, b, c Results of experiments on a olivine ugandite with H
2
O only. All H
2
O added by
weight. Open symbols: above liquidus, close symbols: below liquidus. (after Edgar et al. 1980).S.
a Liquidus relation under
5 and 15 wt% added H
2
O and water-saturated (25 and 40 wt% H
2
O)
condition. b Detailed phase relations with 5 wt% H
2
O. c Detailed phase relation with 15 wt% H
2
O
'
dry
'
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