Petrogenesis of Off-Axis, Post-Glacial Basalts from Snaefellsnes, Iceland

Iceland post-glacial magmatism (<13ka) is primarily restricted to three neovolcanic on-axis rift zones. Unlike the rift zones, off-axis flank zones produce small volumes (<2%post-glacial magmatism) of transitional to alkaline lavas. Flank zone basalts are generally more enriched in incompatible trace elements and have higher La/Yb and Dy/Yb, indicating a smaller degree of melting and greater average depth of melting (Kokfeltet al., 2006; Peate et al., 2010). The Snaefellsnes Peninsula is one of three flank zones. Snaefellsnes's distance from the rift zones (40-170 km) and the suggested center of the plume (220-330 km) make it well suited to characterize the enriched component of Iceland. Also, because of the limited decompression melting due to poorly developed extensional tectonics and thickened lithosphere, the mechanism for magma genesis and transport has yet to be elucidated. Elemental and isotopic data can be powerful tools used to characterize the chemical composition, heterogeneity, and dynamics of the mantle. Radiogenic isotope data (Pb-Sr-Nd-Hf), stable isotope data (δ¹⁸O), and trace elemental data are used to investigate and constrain magma genesis and mantle heterogeneity at Snaefellsnes. Representative samples were selected from across Snaefellsnes's three volcanic systems: Ljósufjöll, Lysuskard, and Snaefellsjökull, arranged in an en-echelon pattern from east to west. High precision Pb + Sr-Nd-Hf isotopes were analyzed from hand-picked rock chips, olivine-hosted melt inclusions were analyzed for their trace element concentrations, and high precision oxygen isotopes analyzed from hand-picked olivine grains free of inclusions and secondary alteration. Broad east to west trends have previously been defined across the peninsula: increasing alkalinity, increasing trace element enrichment, decreasing silica content, and decreasing ³He/⁴He (Peate et al., 2019). Improved analytical techniques over the past decade and higher density sampling help to resolve these trends. Combining major elemental data with trace element and isotopic data, coupled with previous depth constraints (Maruszczack, 2018), should lead to a robust chemical characterization of the enriched mantle source and a model for melt generation and transport.