Monazite U-Pb dating and 40 Ar- 39 Ar thermochronology of metamorphic events in the Central African Copperbelt during the Pan-African Lufilian Orogeny

Abstract

New SHRIMP U-Pb age data on metamorphic monazite, as well as step-heating 40Ar-39Ar ages on metamorphic biotite, muscovite and microcline, from Katangan metasedimentary rocks of the Central African Copperbelt are presented. These rocks were deformed and metamorphosed during the Pan-African Lufilian Orogeny. Three samples of metamorphic monazite from the Chambishi structural basin give ages of 592 ± 22 Ma, 531 ± 12 Ma and 512 ± 17 Ma, which correspond respectively to the ages of eclogite facies metamorphism, high-pressure talc-kyanite whiteschist metamorphism, and of a regional metamorphism/mineralisation pulse elsewhere within the Lufilian Orogen. A biotite population from Luanshya gives a 40Ar/39Ar plateau age of 586.1 ± 1.7 Ma, coinciding with the oldest monazite age. Several samples from the Chambishi basin and the Konkola area give 40 Ar/39Ar biotite plateau ages in the range of 496.6 ± 0.6-485.2 ± 0.9 Ma, and a muscovite plateau age of 483.6 ± 1.1 Ma, which are a manifestation of regional uplift and cooling that affected the whole Katangan basin. The youngest apparent 40Ar/39Ar ages obtained are from microcline at Musoshi and range from 467.0 ± 2.7 Ma to 405.8 ± 3.8 Ma, reflecting continued slow cooling of the Lufilian Orogen.