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The Rocks of the Lupata Gorge and the North Side of the Lower Zambezi

Published online by Cambridge University Press:  01 May 2009

F. Dixey  and
W. Campbell Smith
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Extract

The alkaline volcanic rocks of the Lupata Gorge were described in 1915 by E. O. Teale and R. C. Wilson, and in 1922 F. P. Mennell showed that at the entrance to the gorge these rocks were preceded by a sheet of columnar rhyolite intercalated between two series of sediments, for which he proposed the name of the Upper and Lower Lupata Sandstones respectively; the Lower series rested on Karroo basalts, and these upon Karroo sandstones. In 1923, E. O. Teale and W. Campbell Smith gave a detailed petro-graphical description of certain of the alkaline lavas and of the intrusive olivine-nephelinite (nepheline-basalt) of Sena Hill on the south side of the Zambezi.

Type
Original Articles
Information
Geological Magazine , Volume 66 , Issue 6 , June 1929 , pp. 241 - 259
Copyright
Copyright © Cambridge University Press 1929

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References

page 241 note 1 Geogr. Journ., vol. xiv, 1915, p. 31Google Scholar, and also Teale, E. O., Trans. Geol. Soc. S. Africa, vol. xxvi, 1923, p. 103.Google Scholar

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page 241 note 4 The main part of the paper is written by Dr. F. Dixey: the petrography by W. C. S.

page 241 note 5 Dixey, F., “Nyasaland Protectorate,” Annual Report of the Geological Survey Department for the year 1928, pp. 7–8Google Scholar. A short account of the physiographical features of the Lupata Gorge has been given elsewhere. Dixey, F., Geogr. Journ., vol. lxxii, 1928, pp. 454–5, 2 pls.CrossRefGoogle Scholar

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page 242 note 2 The Rift Valleys and Geology of East Africa, 1921, p. 105.Google Scholar

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page 250 note 4 The specimen [N 619] from 2 miles north of the proposed bridge site is a limburgite. The hand-specimen is compact, blackish-slate in colour, and shows a few small phenocrysts of olivine (1–2 mm.) in an aphanitic groundmass. Under the microscope it is seen to consist of very small phenocrysts and microphenocrysts of colourless olivine in a mass of very slender microliths of pale buff (tilleul-buff) augite and a small amount of dark isotropic interstitial material. The last consists of colourless glass crowded with extremely minute opaque cubes and grains (0·006 mm.), chiefly magnetite, but containing also some rhönite. The section contains occasional xenocrysts of quartz surrounded by a zone of greenish augite and (?) felspar. This rock is a limburgite “of the second kind”, described by H., Bücking. It is closely akin to the olivine-nephelinite (nepheline-basalt) of the hills near Sena, previously described. Other parts of the intrusion might be expected to show the holocrystalline-porphyritic development like that described from Baramwana Hill.

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page 254 note 1 I shall be able to show in another paper that many of the kenytes of Mount Kenya contain porphyritic nepheline as well as anorthoclase and are inseparable petrographically from the Kapitian phonolites: the name kenyte has been retained to cover both.

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