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Fig. 13.7 Interpretation of
water-undersaturated melting
experiments on
madupite +2.9 % H
2
O. The
less-well determined
boundaries are shown as
dashed line for clarity. Some
of the smaller fields are not
labeled (after Barton and
Hamilton 1979). Sp: spinel,
Gt: garnet. Other
abbreviations are same as in
Table
13.1
[
]
Cpx+Gt+
Ol+Ap+L
Cpx+Ph+Gt+Ap+L
30
]
Cpx+Ph+
Ol+Gt
+L
25
[
]
Cpx+Ph+
Ol+L
20
?
?
[
]
15
Cpx+Sp+
L
?
?
?
10
5
Cpx+Ph
+Ol+Lc+L
Cpx+Ol
+Lc+L
1100
1200
1300
1400
T
o
product. The experimental results further indicate that in lavas quenched at high
temperatures and low pressures, leucite and clinopyroxene should be abundant
groundmass phases but in lavas quenched at temperature near the solidus, sanidine
and amphibole should be present in the groundmass in large amount. They further
concluded that absence of sanidine in wyomingite, may suggest that the lava was
quenched at temperatures above those of the reaction between leucite and liquid to
produce sanidine.
13.2.4.3 Phase Relations on a Madupite (up to 3 GPa)
Barton and Hamilton (1979) studied a madupite from Leucite Hills. Analysis of the
rock is given in Table
13.2
. They studied the powdered sample of the rock up to a
pressure of 3 GPa at variable temperatures. Their results are summarized at
Fig.
13.7
, which demonstrate that at low pressures (<0.5 GPa), leucite is the
dominant liquidus phase, but is replaced at high pressure (0.5
-
0.7 GPa) by clino-
pyroxene and olivine and only clinopyroxene (0.7
-
1.25 GPa). At still higher
pressure, clinopyroxene and spinel
(1.25
-
1.75 GPa) and only clinopyroxene
(1.75
3 GPa) are the liquidus phases. Olivine reacts with liquid and probably with
clinopyroxene to yield phlogopite. They further observed the presence of apatite
just above the solidus at pressures lower than 1.5 GPa, or as the fourth phase before
-
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