Hf Isotopic Variations in Volcanic Rocks From the Caribbean Large Igneous Province and Cocos Ridge (Central East Pacific)

The Caribbean Large Igneous Province (CLIP) consists of the Caribbean oceanic plateau and associated magmatic terranes along the Pacific coast of central America and western Colombia and is interpreted to mark the initiation of the Galapagos hotspot 75-95 Ma ago. New 176Hf/177Hf data show: 1) a depleted end-member (176Hf/177Hf_in= 0.28324) represented by lavas from DSDP site 152 ( ~75 Ma) in the central Caribbean, lavas from the young Osa Peninsula ( ~62 Ma) and basalts from the Cocos and Carnegie Ridges portions of the Miocene Galapagos hotspot track, and 2) an enriched end-member (176Hf/177Hf_in = 0.28298) represented by lavas from DSDP site 151 and by the younger Quepos terrane of Costa Rica ( ~59 Ma). Our results support previous interpretations, based on trace elements and Sr, Nd and Pb isotopic ratios (Hauff et al., 2000) that infer mixing between the regular depleted MORB mantle source, or alternatively a depleted plume component derived from recycled oceanic crust, and an enriched Galapagos plume source. Lavas from the Caribbean Island of Curacao and western Colombia have elevated epsilon Hf for a given epsilon Nd relative to the Nd-Hf mantle array, suggesting influence of a pelagic sediment component. Similar Nd-Hf isotope compositions are observed in lavas from the southern Galapagos island of Floreana (Blichert-Toft and White, 2001). High epsilon Hf relative to the mantle array is also observed in a lava from the Malpelo Ridge, part of the Galapagos hotspot track, ~200 km off the coast of Panama. In addition to the regular depleted MORB and enriched plume source, a crustal source component is required to account for the spatial and temporal isotopic variations in the magmatic products of the Galapagos plume. F. Hauff, K. Hoernle, G. Tilton, D.W. Graham and A.C. Kerr (2000) EPSL 174, p.247-263 J. Blichert-Toft and W.M. White (2001) G-cubed, in press