Alkaline Rocks and Carbonatites of the World

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Matsena

stripes

Occurrence number: 
122-00-002
Country: 
Nigeria
Location: 
Longitude: 10.17, Latitude: 13.17

Adjacent to the border with Niger in northern Nigeria over a level plain of blown sand rise occasional rocky hills of arfvedsonite granite with a few volcanic rocks. The area underlain by these rocks, on the Nigerian side of the border, is of the order of 300 km2 (see also Mounio occurrence - Niger No. 121-00-023). The granites, the most extensive and numerous outcrops of which are clustered around Matsena, are all arfvedsonite-bearing with aegirine and sometimes aenigmatite or astrophyllite. Turner (1974) distinguished six petrographic varieties that he considered probably represented distinct intrusions. Other minerals identified include hedenbergite, a calcic amphibole, probably hornblende, amblygonite, zircon, fluorite, allanite and pyrochlore. About 25 km east of Matsena occur a group of hills of volcanic rocks that are rhyolitic and mainly tuffs. The tuffs are generally very fine-grained but in some welded pumice fragments and pieces of rhyolite are present. A more homogeneous rhyolite contains phenocrysts of arfvedsonite, aegirine and aenigmatite in a matrix of quartz and feldspar with a little astrophyllite and spongy crystals of fluorite. In the northern part of the area are outcrops of a granite porphyry the aligned distribution of some of the outcrops suggesting they may be part of a ring-dyke. They contain quartz and perthite phenocrysts with poikilitic amphibole plates zoned from hornblende cores to arfvedsonite rims and aegirine rimmed by arfvedsonite in a groundmass of feldspar and quartz.

Age: 
Rb-Sr determinations on a specimen of arfvedsonite granite and separate light and heavy fractions gave an age of 258(5 Ma (Rahaman et al., 1984).
References: 
RAHAMAN, M.A., VAN BREEMEN, O., BOWDEN, P. and BENNETT, J.N. 1984. Age migrations of anorogenic ring complexes in northern Nigeria. Journal of Geology, 92: 173-84.TURNER, D.C. 1974. The younger granites of the Matsena area, Bornu Province, northern Nigeria. Records of the Geological Survey of Nigeria, 8: 5-19.
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