Synkinematic emplacement of the Pan-African Ngondo igneous complex (west Cameroon, central Africa)

The Ngondo Complex is one of the Pan-African plutons intruded in the West C ameroon Pan-African Orogenic Belt. The complex consists of three major grou ps of rocks: basic to intermediate rocks (diorites, granodiorites and minor gabbros), fined-grained granites and coarsed-grained granites successively emplaced in a metamorphic country rock of amphibolite-facies. Synkinematic emplacement of the complex, in relation with a ductile mega shear zone, is documented by a study of microstructures and foliation patterns which indi cate a continuous transition from magmatic to high temperature solid-state deformation. The geometry of the internal foliation trajectories and the jo int orientation in the complex suggest that the emplacement of the three gr oups of rocks was totally controlled by a N30 degrees sinistral shear zone. Emplacement mechanisms, which are related in time and space to a continuum of deformation, may indicate a relative rheological change of the crust fr om ductile to brittle behaviour. (C) 1999 Elsevier Science Limited. All rig hts reserved.