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Continental flood basalt lavas often contain deeply-sourced, thermo-chemically anomalous material that can provide a potential probe of inaccessible reservoirs. However, continental flood basalts interact with geochemically diverse domains within the continental lithosphere, which may complicate interpretations of deep mantle signatures. We examine the role of continental lithospheric mantle in continental flood basalts erupted as part of the 1.1 Ga Keweenawan large igneous province, centered on the Lake Superior region of North America. We show that flood basalts at Mamainse Point exhibit a range of [epsilon].sub.Hf 1100 from -14.1 to +6, plotting along the global [epsilon].sub.Hf-[epsilon].sub.Nd mantle array. Lithospheric mantle melts represented by alkaline rocks from the Coldwell and Seabrook Lake Complexes yield positive [epsilon].sub.Nd 1100 (+0.7 to +4.3) and [epsilon].sub.Hf 1100 from -6.9 to +2.4, placing them below the mantle array. Mamainse Point lavas are interpreted to be variably crustally contaminated melts of the Keweenawan plume and ambient upper mantle; there is no clear evidence for contributions from an enriched lithospheric mantle., Author(s): Tyrone O. Rooney [sup.1], Jasper G. Konter [sup.2], Valerie A. Finlayson [sup.2] [sup.3], Andrew LaVigne [sup.1], Eric L. Brown [sup.4], Carol A. Stein [sup.5], Seth Stein [sup.6], Robert Moucha [...]

Several magmatic processes contribute to the Fe isotope composition of igneous rocks. Most basalts fall within a limited range of δ 56 Fe ( + 0.10 ± 0.05 ‰ ), although more differentiated lavas trend towards slightly elevated values (up to + 0.3 ‰ ). New data for basalts and olivine crystals from the Samoan Islands show higher δ 56 Fe values than have previously been reported for basalts worldwide. Common magmatic processes – from partial melting of average mantle to subsequent differentiation of melts – cannot sufficiently fractionate the Fe isotopes to explain the elevated δ 56 Fe values ( ∼ + 0.3 ‰ ) in rejuvenated Samoan lavas. Instead, a mantle source with an elevated δ 56 Fe value – in conjunction with effects due to common magmatic processes – is required. The Samoan mantle source is known to be unique in its radiogenic isotope composition and indications that melting of the Samoan mantle source can generate elevated δ 56 Fe values in lavas comes from: (1) High f O 2 values of Samoan lavas and their likely sources affecting Fe isotope fractionation during melting; (2) Metasomatism that caused elevated δ 56 Fe in the Samoan mantle, as observed in xenoliths; and (3) Involvement of a pyroxenite source lithology, based on the Zn/Fe ratios and TiO 2 (and other high field-strength element) abundances of the lavas, that can generate melts with elevated δ 56 Fe values. Two models are presented to explain the elevated δ 56 Fe values in Samoan lavas: a metasomatized source ( ∼ + 0.07 ‰ ) or the presence of a pyroxenite source component ( ∼ + 0.12 ‰ ). Both models subsequently elevate δ 56 Fe values with both partial melting ( ∼ + 0.14 ‰ ) and fractional crystallization ( ∼ + 0.1 ‰ ). These processes may be related to an upwelling mantle plume with a pyroxenite component, or melting of previously metasomatized upper mantle. [ABSTRACT FROM AUTHOR]