Subduction and terrane collision stabilize the western Kaapvaal craton tectosphere 2.9 billion years ago

Integrative models of crust and mantle structure, age, and growth of the oldest continental nuclei-the Archean cratons-are critical to understanding the processes that stabilize continental lithosphere. For the Kaapvaal craton of southern Africa, conflicting ages of stabilization have been derived from studies of its crust and underlying mantle. New U-Pb zircon geochronological data from the western Kaapvaal craton reveal that two older (3.7 to 3.1 billion year old) continental masses, the Kimberley and Witwatersrand blocks, were juxtaposed by a significantly younger, previously unresolved episode of subduction and terrane collision between 2.93 and 2.88 billion years ago. Geological evidence indicates that convergence was accommodated by subduction beneath the Kimberley block, culminating in collisional suturing in the vicinity of the present-day Colesberg magnetic lineament. The timing of these convergent margin processes is further shown to correlate with the strong peak in Re-Os age distributions of Kimberley block mantle peridotites, eclogites, and eclogite-hosted diamonds. These data thus support the petrogenetic coupling of continental crust and lithospheric mantle through a model of continental arc magmatism, subduction zone mantle wedge processing and terminal collisional advective thickening to form Archean continental tectosphere. (C) 2004 Elsevier B.V. All rights reserved.