Neoproterozoic thermal events and crustal growth in the Zambezi Belt, Zambia: New insights from geothermobarometry, monazite dating, and detrital zircon geochronology of metapelites

The Zambezi Belt located in southern Zambia and northern Zimbabwe forms part of the E-W-trending Kuunga orogen associated with the amalgamation of Gondwana supercontinent. The belt consists of a crystalline basement unconformably overlain by a supracrustal sequence of meta-pelites/psammites, calc-silicates, meta-car-bonates, and magmatic rocks. Monazite-bearing meta-pelites are distinguished by petrography, geothermobarometry, monazite chemistry, and detrital provenance. The studied samples include six garnet-bearing schists with biotite, plagioclase, quartz, muscovite +/- staurolite +/- kyanite from the Nega Formation, and three kyanite-mica schists with chlorite, quartz, and accessory rutile, ilmenite, tourmaline from the Chipongwe Formation. Phase equilibria modelling and isopleth geothermobarometry identified Barrovian-type medium-T/medium-P facies peak conditions of 570-665 degrees C/6.5-9 kbar on garnet-bearing schists, and 600-663 degrees C/similar to 8.8-12 kbar on kyanite-mica schists. Evidence from detrital geochronology suggests that the two formations are stratigraphically equivalent, but electron microprobe dating on monazite suggests they underwent different tectonothermal histories. Monazite ages indicate metamorphism and crustal growth from similar to 650-579 Ma in 3 of the garnet-bearing schists of the Nega Formation, and similar to 550-500 Ma in one of the kyanitemica schists of the Chipongwe Formation. Dating of detrital zircon by LA-ICP-MS indicates local and distal sediment sources including Neoarchean to Paleoproterozoic (2633-1800 Ma) and Meso- to Neoproterozoic (1700-852 Ma). A tectonic cycle of burial metamorphism to exhumation is indicated by clockwise P-T-t paths along different geothermal gradients. The rock units were brought together during collision between the Congo and Kalahari Cratons and final assembly of Gondwana.

Automated summary

The Zambezi Belt in southern Zambia and northern Zimbabwe is part of the Kuunga orogen, associated with the amalgamation of the Gondwana supercontinent. The belt consists of a basement and a supracrustal sequence, with different rock types. Petrographic and geothermobarometry analyses identified the presence of monazite in the crust, and revealed different tectonothermal histories. The rock units were brought together during the collision of the Congo and Kalahari Cratons.