| Summary: | Abstract - Late Cretaceous matic volcanic sequences in Western Colombia and in the southern Caribbean have a striking coherence in their chemistry and compositional range which suggests they are part of the same magmatic province. The chemical characteristics of the majority of the matic lavas are totally unlike those of island arc or marginal basin basal@, so the sequences cannot represent accreted arc terranes. On the other hand their trace element characteristics closely resemble those of IcelandicIReykjanes Ridge basahs that represent an oceanic plateau formed by extensive decompression melting of an uprising deep mantle plume. The occunence of komatiites on Gorgona and high-MgO picritic lavas in SE. Colombia and on Curacao, representing high temperature melts of the plume tail, confirms this analogy. Likewise, late stage rhyolites within the Colombian mafrc volcanics may well be the equivalent of the extensive silicic magmas on Iceland and at Galapagos, possibly formed by remelting of the deep parts of the overthickened basaltic crust above the plume head. These volcanics, plus others around tbe Caribbean, including the floor of the Central Caribbean, probably all represent part of an oceanic plateau that formed rapidly at the Galapagos hotspot at 88 Ma, and that was too hot and buoyant to subduct beneath the margin of S. America as it migrated westwards with the opening of the South Atlantic, and so was imbricated along the continental margin. Minor arc-like volcanics, tonalites and hornblende leucogabbro veins may represent the products of subduction-flip of normal ocean crust against the buoyant plateau, or hydrous melts developed during imbricatiotiobduction. Copyright 0 1996 Elsevier Science Ltd & Earth Sciences & Resources Institute
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