Geology Reference
In-Depth Information
4.3.2 Korath Range, Ethiopia
There is a small group of volcanoes in Korath Range of southern Ethiopia (Brown
and Carmichael 1969). The basement rocks of these volcanoes are constituted of
basanites and tephritic lavas, which are characterized by the presence of pheno-
crystal olivine, phlogopite, leucite and nepheline in a groundmass of plagioclase,
olivine, phlogopite, leucite and nepheline. Ti-poor kaersutite has also been found to
be an accompanying phase. The analyses of plagioclases show that their compo-
sitions vary from An
80
to An
52
. The pyroxenes are titanaugites containing signif-
icant amount of alumina as CaAl
2
SiO
6
or CaTiAl
2
O
6
molecules in solid solutions.
Leucite contains 1
1.5 wt% Na
2
O in solid solution.
-
4.3.3 The Kapamba Lamproites of the Luangwa Valley,
Eastern Zambia
A group of pipes and dikes of lamproitic rocks occur along the Kapamba River, a
tributary of the Luangwa River, about 150 km west
northwest of Chipata in Eastern
Zambia (Scott Smith et al. 1987). The Kapamba lamproites occur in the Irumide
tectonic belt of the Kibaran Province. The intrusive bodies are con
-
ned to the
downfaulted Luangwa Graben, trending northeast. Scott Smith et al. (1987) con-
sider the major faulting events took place at
first during the post Karoo and early
Jurassic period and later during Tertiary to Recent time.
The Kapamba Lamproites exhibit a NW
-
SE trend, which differs from the
NNE
SSW-trending fault of the Luangwa Graben. There are three other provinces
of post Karoo intrusions, which are also associated with Luangawa Graben. Panela
and North Lungawa
-
fields occur respectively, within 150 km east and northeast of
Kapamba; and the Isoka group lies 300 km away in the northern part of the
Luangawa Valley.
The Kampaba lamproites comprise 14 pipe-like bodies (P
1
-
P
14
) occupying a
25 km long NW
SE-trending zone. Based on Rb
Sr mica analyses, C.B. Smith
-
-
(cited by Scott Smith et al. 1987)
fixed the age of the lamproites at 220 Ma.
The pipes are mainly composed of volcanoclastic materials and the clast includes
juvenile lapilli with rounded pebbles of quartz (derived presumably from the
country rocks). The xenoliths include older metamorphic basement rocks.
According to these investigators, the rocks are mostly lapilli tuffs differing in grain
size. The tuffs include graded bedding suggesting pyroclastic
flows. Presence of
cross-bedding indicates pyroclastic surge deposits.
Magmatic rocks often include autolithic breccia, and in many regions, evidence
of multiple intrusions is noted. The pipe rocks display concentric structure having
xenocrysts of crustal rocks in the marginal tuff with signs of crater collapse. The
geology of these pipes is similar to the West Kimberley pipes (Ellendale 4 and 9
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