Magma distribution and crustal extension in the Nigerian younger granite province: evidence from the wase area

Abstract

In the Wase area, situated E of the main belt of Jurassic (Younger Granite) ring complexes in Nigeria, the following sequence of events associated with Younger Granite magmatism took place: (1) Emplacement of minor syenite-granite central complexes and local felsite and microgranite dyke swarms; (2) dextral movement on the ENE-trending Dengi shear zone; (3) emplacement of an extensive swarm of mafic dykes. The S-shaped distribution pattern of ring complexes in the Nigerian Younger Granite province resembles a N-S spreading ridge truncated by ENE-trending transform faults. In the Wase area, the Dengi shear zone can be interpreted as an eastward continuation of the southern transform fault, developed in response to crustal extension in the N-S ‘ridge’ sector—the ring complex belt. The later mafic dyke swarm is correlated with a widespread Jurassic thermal event, known from basement rejuvenation ages W of the ring complex belt, and providing evidence for a much wider development of magma than is indicated by the closely grouped ring complexes.