Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galapagos hot spot tracks

[1] We report Hf isotope compositions of 79 lavas that record the early (similar to5-95 Ma) history of the Galapagos plume volcanism. These include lavas from the Caribbean Large Igneous Province (CLIP; similar to95-70 Ma), the accreted Galapagos paleo-hot spot track terranes (54-65 Ma) of Costa Rica (Quepos, Osa and Burica igneous complexes), and the Galapagos hot spot tracks (<20 Ma) located on the Pacific seafloor (Cocos, Carnegie, Malpelo, and Coiba Ridges and associated seamounts). These samples have previously been well characterized in terms of major and trace elements, Sr-Nd-Pb isotopes and Ar/Ar ages. As a result of the relative immobility of the high field strength and rare earth elements during syn- and post-emplacement hydrothermal activity and low-temperature alteration, combined Lu-Hf and Sm-Nd isotope systematics, when used in conjunction with Pb isotopes, provide a particular powerful tool, for evaluating the source compositions of ancient and submarine lavas. The combined Nd-Hf isotope data suggest that three of the isotopically distinct source components found today in the Galapagos Islands (the Floreana-like southern component, the Fernandina-like central component, and the depleted Genovesa-like eastern component) were present in the CLIP already by 95-70 Ma. The fourth Pinta-like northern component is first recorded at about 83-85 Ma by volcanism taking place during the transition from the plume head/CLIP to plume tail stage and has then been present in the hot spot track continuously thereafter. The identification of the unique northern and southern Galapagos Plume Hf-Nd-Pb isotope source signatures within the CLIP and the oldest hot spot track lavas provides direct evidence that the CLIP represents the plume head stage of the Galapagos hot spot. Hafnium isotopes are consistent with the possibility that two types of sediment components may have contributed to the Hf, Nd and Pb isotope compositions of the Galapagos plume lavas. One component, characterized by Delta Pb-207/Pb-204 approximate to 0 and high positive Delta epsilon Hf has an isotope signature indicative of relatively recently recycled pelagic sediment, a signature typical of the southern Galapagos island Floreana. The other component has an EM like isotopic composition resembling modern seafloor sediments with positive Delta Pb-207/Pb-204 and lower Delta epsilon Hf, a signature typical of the northern Galapagos island Pinta.