Unravelling the mantle cargo and magmatic history of ultramafic lamprophyres from the Delitzsch carbonatite complex, Saxony, Germany

The Delitzsch carbonatite complex, located 25 km NW of Leipzig, constitutes a late Cretaceous ultramafic lamprophyre (UML)-carbonatite occurrence covered by Cenozoic sediments [1,2]. We have analysed UML samples from drillcores for their mineral chemistries by electron-probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to better understand their mantle source and magmatic history.

Based on their mineralogy, the rocks can be classified as alnöite, olivine-alnöite, phlogopite-olivine alnöite, and damtjernite [3]. Compositionally, the rocks lie between UMLs and kimberlites with Mg# [= Mg/(Mg+Fe)] ranging from 0.72 to 0.79, and are likely derived from partial melting of carbonated peridotite at pressures of around 5 GPa [4]. Their deep origin is further corroborated by a garnet-peridotite mantle xenolith which equilibrated at 1350 °C and 5.8 GPa.

Olivine is the most common mineral in the studied rocks and exhibits complex zonation. The core compositions show different groups that we attribute to i) mantle xenocrysts (high Mg# and NiO), ii) antecrysts which have crystallized at different levels in the lithosphere (variable Mg# and NiO), and iii) carbonatitic olivines (extremely low NiO). The rims show distinct differentiation trends converging to Mg# of about 0.87 with decreasing NiO contents.

Our results demonstrate the complex magmatic history of the Delitzsch UMLs and provide evidence for a formerly thick lithospheric mantle beneath Central Europe.

[1] Seifert et al. (2000) Lithos 53: 81-100
[2] Krüger et al. (2013) Chem Geol 353: 140-150
[3] Tappe et al. (2005) JPet 46: 1893-1900
[4] Gudfinnsson & Presnall (2005) JPet 8: 1645-1659