Intermediate and acid igneous rocks of the late-Mesozoic Okenyenya (Okonjeje) igneous complex, Namibia, are almost exclusively syenitic in composition. Microgranite occurs only as rare dykes and sills. Two rock types, syenite and quartz syenite, are readily distinguishable on petrographical and chemical grounds. They form very numerous intrusions including a circular peripheral ring dyke 4.5 km in diameter and are interpreted as being subvolcanic in origin. A close structural relationship is inferred between the ring dyke and an intricate series of subparallel curved intrusive sheets in the southwestern part of the complex. It is suggested that the latter formed through the injection of syenitic magmas into fractures developed in a foundering central block as a result of cauldron subsidence along the ring fault. Significant variations in composition between the two intrusive rock types, and the markedly heterogeneous character of the quartz syenite, may be explained by the tapping of a differentiated and contaminated magma chamber.