Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 0.08, Latitude: 20.72

Tirkine is a nepheline syenite intrusion surrounded by sand that obscures outer contacts. It consists of an outer nepheline syenite ring displaying igneous lamination with a central nepheline syenite intrusion with no apparent directional fabric. The syenite of the ring is a biotite-hastingsite-albite-nepheline syenite within which nepheline-rich and nepheline-poor facies have been distinguished (Liegeois et al., 1991). It is cut in the southwest by an intrusion of sodalite-bearing nepheline syenite. The central intrusion is a medium- to coarse-grained titanite-biotite-hastingsite-nepheline syenite that contains enclaves of a mesocratic, coarse-grained nepheline syenite rich in kaersutite and titanite, which also occurs as a separate intrusion in the southeast. In the centre of the complex is a small body of magmatic breccia consisting of porphyritic mesocratic biotite-diopside-kaersutite malignite with inclusions of a melanocratic malignite. A neck of phonolite is present near the centre of the complex and three outcrops, one 0.5 km across, of nordmarkite occur 4 km to the north.

A Rb-Sr isochron, based on eight whole rock determinations, yielded an age of 215(11 Ma (Liegeois et al., 1991).
LIEGOIS, J.P., SAUVAGE, J.F. and BLACK, R. 1991. The Permo-Jurassic alkaline province of Tadhak, Mali: geology, geochronology and tectonic significance. Lithos, 27: 95-105.
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