Abstract

In a recently mapped region of northern Nigeria, typically syntectonic (“low-level”) granites, surrounded by gneisses, are exposed at the same crustal level as typically late-tectonic (“high-level”) granites, cutting migmatites and metasediments. Comparison with relationships in high-grade metamorphic terranes elsewhere suggests: (1) that low-level granites are root zones of granite masses which rose to comparatively high crustal levels during an orogenic climax; (2) that high-level granites are roof zones of bodies which were emplaced during waning stages of orogenesis and, therefore, did not rise so high. It is our contention that these terms have been inappropriately used to refer to level of granite emplacement, rather than to level of exposure within a granite mass.

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