Tuff dykes of unusual size invade coarser-grained volcaniclastic rocks of the Jurassic Mawson Formation at Coombs Hills and Allan Hills, Antarctica. We infer that the material for the largest dykes was elutriated from their host's matrix. To our knowledge, this mode of genesis has not been invoked before. In this volcanic setting elutriation was driven by magmatic heat, but the production of relatively finer-grained clastic dykes by elutriation of material from coarser ill-sorted sources may be significant in many settings.

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