Alkaline Rocks and Carbonatites of the World

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Zaranda

stripes

Occurrence number: 
122-00-025
Country: 
Nigeria
Location: 
Longitude: 9.6, Latitude: 10.28

This is a somewhat isolated centre forming a prominent hill having an elevation of 600 m above the surrounding plains. It is circular, 5 km in diameter and unusual for the province in consisting predominantly of syenitic rocks. Bennett et al. (1984) distinguished an inner zone, which is an approximately circular area 2.5 km in diameter of trachytic rocks, and an outer zone of syenite and granite which is cut by basic dykes. The inner zone trachytic rocks are fine-grained, variably porphyritic, sometimes brecciated and cut by occasional bodies of syenite porphyry. They are composed of perthite phenocrysts in a matrix of aligned feldspar laths, a little quartz and, in some rocks, ferrohedenbergite and amphibole. The syenite of the outer zone grades outwards into granite, is variably medium- or coarse-grained and consists of perthite, quartz, ferrohedenbergite with sodium-rich rims, and tiny laths of aegirine, a sodic-calcic amphibole, generally as rims on pyroxene, and accessories including aenigmatite and chevkinite. The granite is texturally variable and besides perthite and quartz includes interstitial amphibole and abundant aenigmatite. The basic dykes that cut the outer zone extend into the country rocks and appear to be associated with a basic body located on the southeast of the complex. A gravity survey of the complex is described by Ibe et al. (1985). Pb, Sr and Nd isotope data on two syenites and a trachy-rhyolite are given by Dickin et al. (1991).

Age: 
Six samples gave a Rb-Sr isochron age of 190(15 Ma (van Breemen et al., 1975).
References: 
BENNETT, J.N., TURNER, D.C., IKE, E.C. and BOWDEN, P. 1984. The geology of some northern Nigerian anorogenic ring complexes. Overseas Geology and Mineral Resources, 61: 1-65.DICKIN, A.P., HALLIDAY, A.N. and BOWDEN, P. 1991. A Pb, Sr and Nd isotope study of the basement and Mesozoic ring complexes of the Jos Plateau, Nigeria. Chemical Geology (Isotope Geoscience Section), 94: 23-32.IBE, K.K., AJAKAIYE, D.E. and OJO, S.B. 1985. Gravity interpretation of the Zaranda younger granite ring complex, Nigeria. Journal of African Earth Sciences, 3: 253-9.VAN BREEMEN, O., HUTCHINSON, J. and BOWDEN, P. 1975. Age and origin of the Nigerian Mesozoic granites: a Rb-Sr isotopic study. Contributions to Mineralogy and Petrology, 50: 157-72.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith