Abstract

The President (Sir Peter Kent) congratulated Dr Maltman on a clear exposition of the problem. He commented that the Author had observed that no contacts of the ultramafic rocks were exposed, and asked whether it was not possible to produce an exposure by an artificial cut.

Dr R. R. Skelhorn wondered whether two of the main pieces of evidence put forward by the author against the solid emplacement of the ultramafic masses, namely, the absence of shearing and the presence of mesh-textured serpentine, were valid. Was it possible that the rocks were sheared during emplacement and that the later process of serpentinization has masked the evidence; the ultramafic masses had acted as sponges to the water in the adjacent country rocks? If, however, the ultramafic masses were not tectonically emplaced then what evidence is there which indicates the nature of the magma and the process by which it crystallized?

Dr N. H. Woodcock commented that, if the regional and small-scale structures were wholly post-emplacement, their style was largely irrelevant to the emplacement problem. Whilst the weight of evidence supported non-tectonic emplacement, the apparent absence of syn-emplacement structures was itself inconclusive. Detailed work on tectonically emplaced Mesozoic ophiolites in Greece (Smith & Woodcock, Proc. 5th Conf. Aegean Geol., in press) had revealed very little minor or major folding obviously associated with emplacement.

Mr A. H. F. Robertson stated that according to the widely accepted definition of an ophiolite—a complete sequence of ultramafic and gabbroic rocks, sheeted dykes and mafic volcanics

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