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Response to the papers by Bailie et al. concerning the age and deposition of the Bushmanland Group (South African Journal of Geology, 110, 59–86) and single zircon ages of the Aggeneys Granite Suite (South African Journal of Geology, 110, 87–110)

Department of Geological Sciences, University of Cape Town, Private Bag, Rondebosch, 7700, South Africa, Present address: Paleoproterozoic Mineralisation Research Group, Dept. of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg, 2006, South Africa, e-mail: russellb@postgrad.uj.ac.za

Richard Armstrong

Research School of Earth Sciences, The Australian National University, Canberra, 0200, A.C.T., Australia, e-mail: richard.armstrong@anu.edu.au

David Reid

Department of Geological Sciences, University of Cape Town, Private Bag, Rondebosch, 7700, South Africa, e-mail: dlr@geology.uct.ac.za

The first 20% of the full text of this article appears below.

We appreciate the comments by Colliston et al. (2008) on our recent publications concerning the age and deposition of the Bushmanland Group and the age of the Aggeneys Granite Suite (Bailie et al., 2007a; b). We welcome the debate around the geological significance of the analytical results but note that this can vary according to the stratigraphic/structural models that themselves evolve. We agree with Colliston et al. (2008) that the Namaqua mobile belt is highly structurally complex, being divided into a number of terranes bounded by major thrust faults and with complex stratigraphic relationships that require disciplined and detailed study. It has, nevertheless, being shown by previous authors (Rozendaal, 1975; Joubert, 1986; Ryan et al. 1986; Lipson, 1990; Laccasie et al., 2006) that despite the structural complexity of the area that various lithological units are consistent across large areas of Namaqualand, albeit that they have been duplicated by thrusting, faulting, shearing and other tectonic events.

Colliston et al. (2008) argue for a "preferable" stratigraphic framework. This preferable stratigraphic framework is, however, arguable and not factual. We have used a stratigraphic subdivision proposed by previous authors and do not prefer to follow the exceedingly complex proposed stratigraphic framework of Colliston et al. (2008) and previous publications of theses authors. The samples used in our . . . [Full Text of this Article]