Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Wasaki Peninsula And Ruri Hills Phonolites


Occurrence number: 
The Wasaki Peninsula
Longitude: 34.37, Latitude: -0.52

On the Wasaki Peninsula and in an area extending southwards around North and South Ruri are some 70 plugs which are predominantly phonolite but with two trending towards nephelinite. They range in diameter from 50 to 700 m, are circular or elliptical in plan and form prominent hills up to 100 m high. Ijolite xenoliths occur in many of the plugs west of the Ruri Hills and basement xenoliths, including fenitized granite, have also been found. The phonolite contains phenocrysts of sanidine, nepheline and pyroxene zoned outwards from augite to aegirine in a glassy to very fine-grained matrix of the same minerals with natrolite and analcime in some rocks. Two plugs consist of phlogopite phonolitic nephelinite in which feldspar is less abundant, the matrix is coarser and of euhedral nepheline and pyroxene and characteristic phlogopite. They contain rare xenoliths of phlogopite pyroxenite.

K-Ar (whole rock) on phonolite gave 10.6±0.3 Ma (Le Bas, 1977, Appendix 1).

LE BAS, M.J. 1977. Carbonatite-nephelinite volcanism: an African case history. John Wiley, London. 347 pp.

Fig. 3_111 The distribution of phonolite plugs on the Wasaki Peninsula and around North and South Ruri (after Le Bas, 1977, Fig. 13.1).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith