Olivine in ultramafic lamprophyres (alnöites) from the Delitzsch Carbonatite complex, Germany, reveals their mantle cargo and magmatic history

The Delitzsch Carbonatite Complex (DCC) in Saxony, Germany, is a Late Cretaceous ultramafic lamprophyre (UML)‑carbonatite complex covered by Cenozoic sediments. To better understand the mantle cargo and magmatic history of the UMLs, we present a microanalytical investigation of UML samples retrieved from drill cores. All samples are highly silica-undersaturated (whole-rock Mg# of 0.81–0.87), contain melilite, and can thus be classified as alnöites. Fresh and abundant olivine exhibits complex zonation with core compositions revealing different groups including i) mantle xenocrysts (high Mg# and NiO, low CaO and MnO), ii) antecrysts (variable Mg# and NiO, elevated CaO and MnO), and iii) carbonatitic olivines (low Mg# and NiO, high MnO). The magmatic olivine rims show distinct differentiation trends converging to Mg# of ~0.87 at decreasing NiO and increasing CaO and MnO contents. Based on trace element systematics, the xenocrystic cores can further be attributed to spinel-peridotites. The magmatic rims show enrichment in Ti, Li, Al, Zn, Y and depletion in V, Cr, Co, Cu, compared to the cores. The group of high‑iron, low-nickel (HILN) olivines can be linked to carbonatitic olivines based on high Mn, Li, P, Zn, Y, Nb, Sr and low Al, V, Cr, Co, Cu concentrations. Thermobarometry indicates that spinel-peridotitic olivine cores equilibrated at temperatures of ~907–965 °C, and that magmatic temperatures of the alnöites were ~ 1120–1190 °C. Our findings demonstrate the complex magmatic history recorded in UMLs of the DCC and provide further evidence for a formerly thick lithospheric mantle beneath Central Europe.