Geochemistry of noble gases and co2 in fluid inclusions from lithospheric mantle beneath wilcza góra (Lower silesia, southwest Poland)

Abstract

Knowledge of the products originating from the subcontinental lithospheric mantle (SCLM) is crucial for constraining the geochemical features and evolution of the mantle. This study investigated the chemistry and isotope composition (noble gases and CO2 ) of fluid inclusions (FI) from selected mantle xenoliths originating from Wilcza Góra (Lower Silesia, southwest Poland), with the aim of integrating their petrography and mineral chemistry. Mantle xenoliths are mostly harzburgites and sometimes bear amphiboles, and are brought to the surface by intraplate alkaline basalts that erupted outside the north-easternmost part of the Eger (Ohře) Rift in Lower Silesia. Olivine (Ol) is classified into two groups based on its forsterite content: (1) Fo88.9−91.5, which accounts for a fertile-to-residual mantle, and (2) Fo85.5−88.1, which indicates large interactions with circulating (basic) melts. This dichotomy is also related to orthopyroxene (Opx) and clinopyroxene (Cpx), which show two ranges of Mg# values (87–90 and 91–93, respectively) and clear evidence of recrystallization. CO2 predominates within FI, followed by N2. The δ13 C of mantle CO2 varies between −4.7‰and −3.1‰, which mostly spans the MORB range (−8‰ < δ13 C