Early Archaean component (greater than 3.5 Ga) within a 3.05 Ga orthogneiss from northern Nigeria: U-Pb zircon evidence

Details Early Archaean component (greater than 3.5 Ga) within a 3.05 Ga orthogneiss from northern Nigeria: U-Pb zircon evidence Early Archaean component (greater than 3.5 Ga) within a 3.05 Ga orthogneiss from northern Nigeria: U-Pb zircon evidence

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.125...89b&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 125, no. 1-4, p. 89-103

Computer Science

1

Chemical Composition, Geochemistry, Geochronology, Geomorphology, Gneiss, Lead (Metal), Nigeria, Orography, Silicates, Single Crystals, Uranium, Zirconium Compounds, Crystal Growth, Earth Crust, Magma, Mountains

Scientific paper

Conventional U-Pb analyses on selected single zircon grains and on zircon fractions from a granodioritic orthogneiss at Kaduna (northern Nigeria) show that the Nigerian basement contains Archaean components that have not been recognized until now. A distinct U-rich zircon group records an age of 3040 +/- 60 Ma, which is interpreted as the age of emplacement and crystallization of the granodioritic magma. The occurrence of a magmatic event at ca. 3000 Ma is confirmed by the addition of core-free abraded grains (3050 +/- 23 Ma). These ages are identical to the less precise value (2980 +/- 90 Ma) given by zircon fractions. These results also demonstrate that zircons underwent Pb loss during the Pan-African orogeny at 612 +/- 23 Ma, which is well supported by an identical age on a single monazite grain (618 +/- 8 Ma). Moreover, U-Pb analyses of abraded U-poor core-bearing crystals clearly identify the presence of source material of early Archaean age (greater than 3500 Ma), the oldest age for crust initiating processes ever found in this area. In contrast to earlier Rb-Sr geochronology no evidence for an Eburnean (2000 +/- 200 Ma) or Kibaran (1100 +/- 200 Ma) orogeny is present in the U-Pb systems of these zircons.

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