Probing the deep central European lithosphere: In-situ Sr isotope analysis of a sheared garnet peridotite xenolith

Mantle xenoliths give insights into igneous processes in the lithospheric mantle. Although spinel peridotite xenoliths from the Central European Volcanic Province have been studied extensively, the deeper central European sub-continental lithospheric mantle remains poorly understood due to the rarity of xenoliths from greater depths. Notably, the Delitzsch carbonatite complex in Germany hosts alnöite dikes (melilite-bearing ultramafic lamprophyres) that contain garnet-peridotite xenoliths [1]. To better characterise the deep lithosphere beneath central Europe, we investigated the radiogenic Sr isotope composition of a sheared garnet peridotite that was entrained from a depth of 190 km (5.9 GPa) by a Delitzsch complex alnöite [2]. We performed in-situ Sr isotope analyses on clinopyroxenes using a 193 nm Excimer laser ablation system coupled with a Neoma MC-ICPMS/MS. The use of SF₆ in the Neoma reaction cell enables interference-free measurement of SrF⁺ ions [3]. The analysed clinopyroxenes exhibit indistinguishable initial ⁸⁷Sr/⁸⁶Sr of 0.7051 ±16, which largely overlaps with the host alnöite (0.704 and 0.70336) [4,5]. The results are consistent with a scenario where refertilization of the lower lithosphere due to prolonged magmatic activity along with a shift to extensional tectonics during the Cretaceous triggered the destabilization and removal of the lower 50–70 km of northern Bohemian Massif lithosphere [2].

[1] Möckel et al. (2023), Geoprofil des LfULG 17, 82-136

[2] Röper et al., in review

[3] Craig et al. (2021), Anal. Chem. 93, 10519-10527

[4] Wand et al. (1987), Fifth Working Meeting Isotopes in Nature, 421-436

[5] Krüger et al. (2013), Chem. Geol. 353, 140-150