Magma source evolution beneath the Caribbean oceanic plateau: New insights from elemental and Sr–Nd–Pb–Hf isotopic studies of ODP Leg 165 Site 1001 basalts
Andrew C. Kerr, D. Graham Pearson, Geoff M. Nowell, 2009. "Magma source evolution beneath the Caribbean oceanic plateau: New insights from elemental and Sr–Nd–Pb–Hf isotopic studies of ODP Leg 165 Site 1001 basalts", The Origin and Evolution of the Caribbean Plate, K. H. James, M. A. Lorente, J. L. Pindell
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Ocean Drilling Project Leg 165 sampled 38 m of the basaltic basement of the Caribbean Plate at Site 1001 on the Hess Escarpment. The recovered section consists of 12 basaltic flow units which yield a weighted mean Ar/Ar age of 80.9±0.9 Ma. The basalts (6.4–8.5 wt% MgO) are remarkably homogeneous in composition and are more depleted in incompatible trace elements than N-MORB. Depleted initial radiogenic isotope ratios (ɛNd +11.1 to +11.9; ɛHf +15.2 to +16.9; 87Sr/86Sr 0.7025–0.7028; 206Pb/204Pb 18.34–18.50; 207Pb/204Pb 15.42–15.51; 208Pb/204Pb 37.64–37.90) reveal a long-term history of depletion. Although the Site 1001 basalts are superficially similar to N-MORB, radiogenic isotopes in conjunction with incompatible trace element ratios show that the basalts have more similarity to the depleted basalts and komatiites of Gorgona Island. This chemical composition strongly implies that the Site 1001 basalts are derived from a mantle plume-depleted component and not from depleted ambient upper mantle. Therefore the Site 1001 basalts are, both compositionally and tectonically, a constituent part of the Caribbean oceanic plateau. Mantle melt modelling suggests that the Site 1001 lavas have a composition which is consistent with second-stage melting of compositionally heterogeneous mantle plume source material which had already been melted, most likely to form the 90 Ma basalts of the plateau. The prolonged residence (>10 Ma) of residual mantle plume source material below the region confirms computational model predictions and places significant constraints on tectonic models of Caribbean evolution in the Late Cretaceous.
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The Origin and Evolution of the Caribbean Plate
This book considers the geology between North and South America. It contributes to debate about the area's evolution, particularly that of the Caribbean. Prevailing understanding is that the Caribbean formed in the Pacific and was engulfed between the Americas as the latter drifted west. Accordingly, the Caribbean Plate comprises internal, Jurassic–Cretaceous oceanic rocks, thickened into a Cretaceous hotspot/plume plateau, with obducted ophiolites and Cretaceous–Palaeogene, subduction-related, intra-oceanic volcanic arc and metamorphosed arc/continental rocks exposed on its margins. An alternative interpretation is that the Caribbean evolved in place. It consists largely of continental crust, extended in the Triassic–Jurassic, which subsided below thick Jurassic–Cretaceous carbonate rocks and flood basalts, and Cenozoic carbonate and clastic rocks. After uplift of ‘oceanic’ and volcanic arc rocks onto (continental) margins, the interior foundered in the Middle Eocene. Papers range from regional overviews and discussions of Caribbean origins to aspects of local geology arranged in a circum-Caribbean tour and ending in the interior. They address tectonics, structure, geochronology, seismicity, igneous and metamorphic petrology, metamorphism, geochemistry, stratigraphy and palaeontology.