Geology Reference
In-Depth Information
In the Bufumbira area of Uganda (Holmes and Harwood 1937; p. 98) leucite
basanite locally grades into olivine-poor leucite tephrite). In the Mabunga area,
Holmes and Harwood (1937) found inclusion of leucite tephrites in leucite basa-
nites. Reference to Fig. 9.11 shows the paragenetic relationship between these two
rock types. Leucite tephrites occur at Kitale area, about 24 km to the west of
Bufumbira, where leucite tephrites are found in association with leucite basanite.
Figure 9.10 suggests that if the composition of liquid lies close to the diopside
-
leucite join inside the system diopside
anorthite, a leucitite magma will
yield a leucite tephrite. Holmes and Harwood (1937) described lava
leucite
-
-
flows of leucite
basanite from the following areas of the Birunga (Chap. 4 ) petrographic province:
Busumba, Mihanga, Mabungo, Kumizika, Ishozi, Nyakimanga, and Lungandable.
Lavas transitional between olivine leucitite and leucite basanitie (Fig. 9.11 ) have
been described from the Kisi area near the northwest corner of Lake Kivu in
Uganda.
Many older volcanic districts to the northwest of Vesuvius are characterized by
leucite tephrites, In the Vulsinian district the lava changes from leucite tephrite to
leucitite and very basic basanites. In some places the later rock types are low in
modal plagioclase and similar to olivine leucitite.
Duda and Schminke (1978) found that leucite basanites crop out at Kunkskopf,
Veitskopf, Rothenberg, Nickenicher Hummerich, Nickenicher Sattel, Heidskopf
and Satelberg in the East Eifel region of West Germany (Fig. 4.17 ) . In Kunkskoph,
the association of leucite tephrite and basanite is found. Leucite tephrite was also
described from Alterberg, E. Eifel by Duda and Schminke (1978).
9.5 The System Diopside - Leucite - Anorthite - SiO 2
The paragenetic relationship between leucite tephrite, phonolite, trachyte, and
potassium-rich latite can be understood from the study of the system diopside
-
leucite
SiO 2 . Experimental results on various joins of the system are
already known. The system has four bounding joins: (1) the join diopside
anorthite
-
-
leu-
-
cite
SiO 2 , (2) the join diopside
anorthite
SiO 2 , (3) the join diopside
leucite
-
-
-
-
-
anorthite and (4) the join leucite
SiO 2 . Temperatures of piercing points of
different bounding joins are summarized in Table 9.1 .
anorthite
-
-
9.5.1 Course of Crystallization of Liquid in the System
Diopside
Leucite
Anorhtite
SiO 2
-
-
-
On the basis of the experimental results on four bounding joins the course of
crystallization of liquid in the system diopside
leucite anorthite
SiO 2 can be
-
-
summarized by a flow sheet diagram (Fig. 9.12 ).
 
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