Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 37.05, Latitude: 4.23

Lying just south of the Ethiopian border in the Sabarei area (Key and Watkins, 1988) the Jibisa ring complex expresses itself as the 675 m high Jibisa Mountain. Earlier diorite and tholeiitic basalts are cut by a central stock 5 km in diameter of peralkaline granite and syenite and porphyritic microsyenite. The microsyenite forms a central irregular intrusion and also dykes that cut the granite and syenite. The granite and syenite contain aegirine which is also found in some of the microsyenite dykes in which nepheline may occur in the groundmass. Chemical analyses of a range of rocks are given by Key and Watkins (1988).

K-Ar determinations on peralkaline granite and porphyritic microsyenite gave 20.7(1.4 and 14.4(0.7 Ma (Key and Watkins, 1988).
KEY, R.M. and WATKINS, R.T. 1988. Geology of the Sabarei area. Report, Geological Survey of Kenya, 111: 1-57.
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