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In-Depth Information
Figure
13.2
further shows that a melilite-nepheline leucitite and a olivine-me-
lilite-nepheline leucitite are represented at 1 and 2.5 GPa by an assemblage cor-
responding to amphibole-phlogopite pyroxenite. Although clinopyroxene was the
last phase to crystallize in the one atmospheric run, it was the
rst phase to crys-
tallize in the high pressure runs. The results of the investigation at atmospheric
pressure showed that the liquidus temperature of 1,197
C is lowered by 82
o
and
°
64
C at 2.5 and 1 GPa, respectively. Microprobe studies show that the
amphibole is a K
±
5
°
Na richterite.
-
13.2.3 Experimental Study on a 79 AD Vesuvian Lava Flow
Shea et al. (2009) made experimental investigation on two samples of a Vesuvian
lava
flow from Italy. The compositions of the two samples are included in
Table
13.2
(Analysis 18 and 19). Their experimental results are summarized in the
Fig.
13.3
a and b. It is observed that pyroxene is the liquidus phase in both the
samples. Amphibole is an accompany phase both the samples. Leucite appears after
both sanidine and plagioclase. The results indicate that the two rocks are leucite-
bearing tephri-phonolite.
Freda et al. (2008) studied a phono-tephrite from Alban hills (Central Italy).
Their study was made in presence of volatiles under 0.5 GPa at variable temper-
atures, the content and nature of volatiles are given in the Fig.
13.4
a
d. The
gures
-
depict only paragenetic relationships of various phases.
13.2.4 Phase Relations on Katungites
13.2.4.1 Investigation on a Synthetic Katungite (up to 1 GPa)
Experimental study was made by Yoder (1973) on a synthetic katungite (akerma-
nite + leucite + forsterite under
fluid pressures of H
2
O and CO
2
(mixed in different
proportions) up to a pressure of 1 GPa. He found that at high pressure the
assemblage consisted of phlogopite, olivine, and calcite, which is similar to the
assemblage of kimberlitic groundmass. A synthetic katungite (Fo
20
Ak
40
Lc
40
)
consisting of forsterite, akermanite and leucite was studied between 1.0 and 2.5 GPa
P(H
2
O), (by Gupta and Yagi 1980) below 1,100
C and was found to convert to an
assemblage consisting of phlogopite, pyroxene, and liquid. At these pressures liquid
appeared at 750
+
25
°
°
C. Breakdown of diopside
ss
+ phlogopite
ss
at low pressures
can be explained by the following reaction,
if the small amounts of solid solutions
in these phases are ignored:
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