THE GEOCHEMISTRY AND TECTONIC SETTING OF LATE CRETACEOUS CARIBBEAN AND COLOMBIAN VOLCANISM

Late Cretaceous mafic volcanic sequences in Western Colombia and in th e 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 mafic la vas are totally unlike those of island are or marginal basin basalts, so the sequences cannot represent accreted are terranes. On the other hand their trace element characteristics closely resemble those of Ice landic/Reykjanes Ridge basalts that represent an oceanic plateau forme d by extensive decompression melting of an uprising deep mantle plume. The occurrence of komatiites on Gorgona and high-MgO picritic lavas i n S.E. Colombia and on Curacao, representing high temperature melts of the plume tail, confirms this analogy. Likewise, late stage rhyolites within the Colombian mafic volcanics may well be the equivalent of th e extensive silicic magmas on Iceland and at Galapagos, possibly forme d by remelting of the deep parts of the overthickened basaltic crust a bove the plume head. These volcanics, plus others around the Caribbean , including the door of the Central Caribbean, probably all represent part of an oceanic plateau that formed rapidly at the Galapagos hotspo t at 88 Ma, and that was too hot and buoyant to subduct beneath the ma rgin of S. America as it migrated westwards with the opening of the So uth Atlantic, and so was imbricated along the continental margin. Mino r are-like volcanics, tonalites and homblende leucogabbro veins may re present the products of subduction-flip of normal ocean crust against the buoyant plateau, or hydrous melts developed during imbrication/obd uction. Copyright (C) 1996 Elsevier Science Ltd & Earth Sciences & Res ources institute