Abstract

T-shaped orogenic triple junctions between mobile belts usually form in two unrelated stages by subsequent and oblique continental collisions separated by a significant time span. Besides these “oblique triple junctions”, another type, named “transverse triple junctions”, may exist. Such junctions are created by a more complex mechanism of partly contemporaneous convergence of three cratons in a restricted time frame, involving strike slip. The Neoproterozoic–Cambrian Kaoko-Damara junction between the Rio de la Plata, Congo, and Kalahari cratons in Namibia is an example of such a transverse orogenic triple junction, formed by at least four subsequent but partly related deformation events. Initial north-south convergence between the Congo and Kalahari cratons was followed by east-west collision of the Rio de la Plata and Congo cratons. Subsequently, the Kalahari and Congo cratons collided, contemporaneous with sinistral strike-slip motion between the Congo and Rio de la Plata cratons and with the intrusion of large granite-syenite plutons, probably associated with slab detachment aided by the strike-slip movement. Other examples of transverse triple junctions may exist in Gondwana. Transcurrent shear zones, some possibly nucleated on transform faults from the pre-collision setting, are essential for the formation of transverse triple junctions.

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