Possible Precambrian Obduction and Plate Tectonics in Southeastern Africa

Abstract

IN the theory of plate tectonics, the term “obduction zone” has been introduced recently1,2 to describe a region where slabs or slices of oceanic crust and mantle have been over-thrust onto a continental margin when the edge of the continental plate came into contact with a downward moving subduction zone. According to this concept, the upthrust, onland slices of oceanic crust are represented by rocks of the ophiolite suite, which is characterized by a three-fold sequence of an upper layer of deep-sea sediments—argillite, chert and pelagic limestone; an intermediate layer of pillow lavas; and a lower layer of mafic and ultramafic rocks. Obduction zones are known in several mountain belts including the Alpine-Himalayan belt3, the circum-Pacific belt4 and the Appalachian-Caledonian system2.