Alkaline Rocks and Carbonatites of the World

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Sara-Fier And Pankshin

stripes

Occurrence number: 
122-00-038
Country: 
Nigeria
Location: 
Longitude: 9.4, Latitude: 9.43

The Sara-Fier complex is about 50 km from north to south and consists of five major ring structures and a syenite stock. The four most northerly centres overlap so their relative ages can be determined with certainty and there is a general younging southwards (Turner, 1963 and 1976). South of Centre 4 is the Pankshin syenite stock south of which is the younger Centre 5, which is probably the youngest centre, but this is not certain because of doubts over the relative ages of Centre 4 and the Pankshin syenite. The complex is almost entirely intrusive but small amounts of volcanic rocks are preserved in Centre 1. Centre 1 was probably the biggest ring structure but much was destroyed by the emplacement of the next two centres. The earliest rocks were volcanics that are preserved in a narrow arcuate down-faulted zone. They comprise rhyolite, basalt, vent agglomerates and porphyry dykes. The intrusive rocks of Centre 1 include a hornblende granite ring-dyke and hornblende-biotite, biotite and aplitic granites. The second centre lies north of Centre 1 and is expressed topographically as the northern Sara Hills. Most of the constituent intrusions are arcuate and an initial ring fracture was followed by a partial ring-dyke of pyroxene-hornblende granite. Other granites are distinguished by the presence of hornblende and/or biotite while a large arcuate granite on the western side, extending for about 10 km, contains arfvedsonite. The ring-dyke granite includes fayalite and a pale-green pyroxene, the exact nature of which does not appear to have been determined, and accessory fergusonite, allanite and fluorite. The arfvedsonite granite is generally a uniformerly coarse-grained rock but porphyritic and pegmatitic facies with large prismatic amphiboles occur near the margins. This rock consists of perthite, prismatic arfvedsonite, which also develops as bundles of radiating fibres, and accessory zircon, astrophyllite, pyrochlore and fluorite. The smaller Centre 3 comprises a biotite and two biotite-hornblende granites and represents southwards progression, which is continued by Centre 4 which is the simplest of the Sara-Fier centres consisting, as it does, of hornblende-biotite and pyroxene-fayalite granites. The fifth centre, known as the Pankshin complex, is the most southerly and is linked to Centre 4 by an intrusion of syenite. The centre comprises concentrically disposed biotite, biotite-hornblende and hornblende-fayalite granites together with a small crescentic hornblende-pyroxene microgranite/quartz syenite on the eastern side. The syenite linking this complex to Centre 4 varies from an almost quartz-free rock to a quartz syenite; mafic minerals are hornblende and a pale-green pyroxene. Badejoko (1976) discusses the petrogenesis of Centres 4 and 5 in some detail and gives modal and chemical data; further rock analyses are available in MacLeod et al. (1971). Data for Li, F and Zr are in Bowden (1966a and 1966b) and Dickin et al. (1991) give Pb, Sr and Nd isotope data for a biotite granite and syenite from Pankshin. Borley (1976a) gives analyses of biotites, amphiboles and pyroxene.

Age: 
A Rb-Sr isochron for biotite granites and syenites of the Pankshin complex gave 154(4 Ma and a K-Ar determination on hornblende from one of these samples 153(7 Ma (van Breemen et al., 1975).
References: 
BADEJOKO, T.A. 1976. Role of adiabatic crystallization and progressive melting in the origin of the Younger Granites - Sara-Fier complex. In C.A. Kogbe (ed) Geology of Nigeria. 195-206. Elizabethan Publishing, Lagos. BORLEY, G.D. 1976a. Ferromagnesian mineralogy and temperatures of formation of the Younger Granites of Nigeria. In C.A. Kogbe (ed) Geology of Nigeria, 159-76. Elizabethan Publishing, Lagos.BOWDEN, P. 1966a. Lithium in Younger granites of northern Nigeria. Geochimica et Cosmochimica Acta, 30: 555-64.BOWDEN, P. 1966b. Zirconium in Younger granites of northern Nigeria. Geochimica et Cosmochimica Acta, 30: 985-93.BUCHANAN, M.S., MACLEOD, W.N., TURNER, D.C., BERRIDGE, N.G. and BLACK, R. 1971. The geology of the Jos Plateau. Volume 2, Younger granite complexes. Bulletin, Geological Survey of Nigeria, 32: 1-159.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.MACLEOD, W.N., TURNER, D.C. and WRIGHT, E.P. 1971. The geology of the Jos Plateau. Volume 1, General geology. Bulletin, Geological Survey of Nigeria, 32: 1-110.TURNER, D.C. 1963. Ring-structures in the Sara-Fier Younger Granite complex, Northern Nigeria. Quarterly Journal of the Geological Society of London, 119: 345-66.TURNER, D.C. 1976. Structure and petrology of the young granite ring complexes. In C.A. Kogbe (ed). Geology of Nigeria. 143-58. Elizabethan Publishing, Lagos.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