Geochemical evolution of the New England seamount chain: Isotopic and trace-element constraints

Abstract

Samples collected by dredge hauls and submersible dives from the New England Seamount (NES) chain, the most prominent of six seamount groups in the Northwest Atlantic Ocean, have been analyzed for Sr, Nd and Pb isotopic compositions and rare-earth and other trace-element contents. Unleached and HCl-leached whole-rock samples, and hornblende and clinopyroxene separates were analyzed in order to obtain isotopic data from the old and altered NES samples. Rare-earth and other trace-element contents were measured on unleached whole-rock samples. The results demonstrate that rimary (unaltered) geochemical data can be derived from older altered oceanic volcanics. The NES have isotopic and trace-element characteristics typical of alkaline volcanics from ocean islands, in particular those characterized by radiogenic Pb isotopic signatures (NES 206 Pb 204 Pb values range up to 20.65). The seamounts exhibit considerable interseamount variation, while intraseamount chemical heterogeneity appears to be substantially less. An increase in radiogenic Pb along the chain towards the southeast is suggested. No other simple geographic trends in chemistry are apparent. The isotopic characteristics of the NES necessitate at least three distinct source components, with substantial involvement of a “radiogenic Pb” type mantle. The isotopic similarities between the NES, Canaries, Azores and Ahaggar imply some type of systematic geographic distribution of this “radiogenic Pb” component.