Late Cretaceous ultramafic lamprophyres and carbonatites from the Delitzsch Complex, Germany

The Delitzsch Complex consists of late Cretaceous ultramafic lamprophyres and carbonatitic rocks. They form dikes and diatremes, emplaced into Palaeozoic to lower Permian volcanic and sedimentary rocks, and are covered by up to 120 m thick sequences of Tertiary sedimentary rocks. The complex includes a diversity of magmatic and subvolcanic rocks. The lithologies range from monchiquites and alkali picrites to dolomite– and calcite–carbonatites (rauhaugites, beforsites, and alvikites), and ultramafic lamprophyres (alnöites, aillikites). Contact relationships and the distribution of xenolithic material indicate that phases of carbonatitic and ultramafic lamprophyre magmatism overlapped. New U–Pb ages (72 ± 1 Ma on baddeleyite) from a dolomite–carbonatite (beforsite), Rb–Sr ages (73 ± 2 Ma on phlogopite) from an ultramafic lamprophyre (alnöite) in combination with modeling of the effect of the initial 87Sr/86Sr of phlogopite on the isochron ages of dolomite– and calcite–carbonatites demonstrate: (1) a short duration of magmatic activity for the main phases of the subvolcanic emplacement of the Delitzsch Complex; (2) phlogopite crystals in carbonatites of the Delitzsch Complex are xenocrysts; (3) the calculated initial 87Sr/86Sr composition of xenocrystic phlogopite equals the initial Sr composition of phlogopite from the alnöite.

► 75 Ma–71 Ma age for the ultramafic–carbonatite complex of Delitzsch ► Xenocrystic phlogopite in carbonatites ► Carbonatites and lamprophyres are coeval and cogenetic