Geochemistry of Neogene magmatism at Spitsbergen Island

Petrological and geochemical data obtained on Neogene magmatism restricted to a deep fault in Andree Land at Spitsbergen Island, which was related to the overall restyling of the Arctic territory at 25–20 Ma, indicate that the derivation of the Neogene magmas was significantly affected by the continental pyroxenite mantle. The Neogene basalts are noted for a radiogenic isotopic composition of Pb (²⁰⁷Pb/²⁰⁴Pb= 15.5–15.55, ²⁰⁶Pb/²⁰⁴Pb = 18.4–18.6, ²⁰⁸Pb/²⁰⁴ Pb = 38.4–38.6) and Sr(⁸⁷Sr/⁸⁶Sr = 0.7038–0.7048) at low ¹⁴³Nd/¹⁴⁴Nd = 0.5129. Melts of this type are the extremely enriched end member of the isotopic mixing of a depleted and enriched sources and determine a geochemical trend that passes through the compositions of alkaline magmas from Quaternary volcanoes at Spitsbergen and weakly enriched tholeiites of the Knipovich Ridge, which started to develop simultaneously with the onset of Neogene magmatism in the western part of Spitsbergen. The composition of the liquidus olivine (which is rich in NiO) indicates that melting occurred in the olivine-free mantle. Our data thus testify that a significant role in the genesis of the Neogene magmas was played by continental pyroxenite mantle.