Melilite- and Leucite-Bearing Systems - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 317

Fig. 10.13 Rock
nomenclature diagram
corresponding to Fig. 10.12
(after Gupta et al. 1973)

M

R
(?)

1175 0

N

1150 0

I
1105 0
B.M.1075 C

0

0

1135 C

P 1258 0

J

kalsilite-rich ultrama field of East Africa. Rock

types (1) and (2) may be represented by points M and P, respectively, of Figs. 10.12
and 10.13 , and melilitite corresponds to point B (Gupta 1972; Fig. 10.1 ). The join
diopside

c rocks (5) from the Toro-Ankole

leucite (Fig. 10.8 ) of Gupta and Lidiak (1973) shows that the
assemblage corresponding to nepheline

nepheline

- -

leucite katungite (Fig. 10.10 ) can be

-

obtained from an olivine nepheline italite. Holmes and Harwood (1937) found

katungite in the region between Bushwaga and Goma of the Birunga area of
Uganda. The assemblage of P (olivine

-

melilite leucitite) is obtained by crystalli-
zation of a liquid from A (Fig. 10.8 ). Rock types corresponding to olivine leucitite
sometimes containing melilite have been reported from more than a dozen localities
by Holmes and Harwood (1937; pp 81

-

82). Important localities include the Lutale

-

flow, south-southwest of Lutale ridge and the Mikeno and Kisi areas (north-east
corner of Lake Kivu). Olivine leucitite lavas with high concentration of olivine
(ugandite) have been reported by Holmes and Harwood (1937; pp. 60

72) from
various areas. Other localities include Muganza, Murehi, Musonga, and Katarara.
The lava

-

leucitite, Fig. 10.13 ),
have been described by the same authors (p. 79) from the following areas of the
same volcanic

flows, corresponding to point R (olivine nepheline

- -

field of Uganda; Mabungo. Duzakara, Bunagana, and Hyamichun-
chu. They also described lava flows of melilite nepheline leucitite (IJ, Figs. 10.12

-

and 10.13 ) from Goma (p. 83), Melilite - nepheline leucitite (Fig. 10.13 ) can be

obtained from olivine nepheline leucitite (I), which has been reported

from the Fort Portal area of Toro-Ankole by Holmes and Harwood (1932, p. 379),
which belongs to the same petrographic province of the Birunga volcanic

- melilite -

field.

Melilite nepheline leucitite has also been reported from the Villa Senni area of Italy

by Washington (1906) and Mt. Vulture (Melluso et al. 1996), the rarity of this rock
type compared to other

-

flow sheet diagram
(Fig. 10.12 ) is probably related to incomplete crystallization of the parent magma.

rock types represented by the