LAM-ICPMS U-Pb dating of kimberlitic perovskite: Eocene-Oligocene kimberlites from the Kundelungu Plateau, DR Congo

Kimberlites are small-volume melts whose eruption is related to weak extension of the lithosphere, and their ages can carry important tectonic information. We have carried out in situ LAM-ICPMS U-Pb dating of groundmass perovskite in two kimberlitic pipes (Kambeli and Msipashi) in Kundelungu Plateau (SE Congo). The method is validated by the analysis of perovskites from four previously dated South African Group I kimberlites. Intercepts of regression lines on inverse-Concordia plots yield precise U-Pb ages (2 sigma=2-6 Ma) and a well-constrained value for the Pb-207/Pb-206 of the common-Pb component. The ages of Group I kimberlites in Kimberley District cluster around 87 Ma, similar to those determined by other techniques demonstrating the robustness of the technique. The perovskites from the Kundelungu kimberlites that are intrusive into the Biano Subgroup (Neoproterozoic Katangan Supergroup) yield an age of 32.3 +/- 2.2 Ma. The Eocene-Oligocene age of the Kundelungu kimberlites corresponds to the opening of the northern part of the East African Rift and implies the southward prolongation of this extension. Considering the position of the Kundelungu Plateau and gravity data for the region, the kimberlite intrusion may reflect extension on the Lake Mweru-Luapula graben. The Luizi impact structure in the Kundelungu Plateau, previously described as Pleistocene, pre-dates the kimberlitic event. (C) 2007 Elsevier B.V. All rights reserved.