Geology Reference
In-Depth Information
The subsolidus assemblage in the join leucite-akermanite-albite
50
anortite
50
at
1 Gpa under H
2
O-saturated conditions comprises wollastonite
ss
, leucite
ss,
nephe-
line
ss,
plagioclase and grossular. In Itapirapua (Saopaulo), Wolley (1987) has
described a similar garnet-wollastonite-plagioclase-Feldspathoid-bearing alkali
complex.
The following conclusions are derived from the study of Dwivedi et al. (2007):
1. Leucite and sodic plagioclase do not coexist in equilibrium. In the join leucite-
akermanite-albite, when leucite coexists with feldspar, it is found to be alkali
feldspar with a compositional rage of An
3-4
Ab
50-53
Or
45-47.
2. In presence of leucite, akermanite and albite react to form diopside
ss,
nephe-
line
ss,
wollastonite
ss,
and alkali feldspar as shown in reaction (
11.1
)
3. In the join leucite-akermanite-albite
50
anorthite
50
, plagioclase coexisting with
leucite was found to be a calcium-rich plagioclase. The An content of Plagio-
clase in equilibrium with leucite was found to vary between 60 and 66 mol%,
the Ab content was observed to be in the range of 17
26 mol%, and the or
content varied between 12 and 17 mol%, When the join leucite-akermanite-
albite
50
-anorthite
50
was studied at 1 GPa in H
2
O-enriched conditions, melilite
was eliminated, as described by the reaction (
11.3
).
-
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