2.09 Ga old eclogites in the Eburnian-Transamazonian orogen of southern Cameroon: Significance for Palaeoproterozoic plate tectonics

摘要: Abstract Lenses of retrogressed eclogites occur in a 100 km wide zone the Nyong Complex, remnant Eburnian-Transamazonian orogen, marking Palaeoproterozoic suture between Congo and Sao Francisco Cratons. The show trace element pattern (depleted LREE) similar to those mid-ocean ridge basalts, indicating that precursor melts formed depleted mantle source from oceanic crust. Despite numerous plagioclase ‘exsolutions’ up 25 mol% jadeite component is preserved omphacite points minimum pressures 16 kbar at c. 800 °C. Pressures may have been 18–20 kbar as indicated by estimated compositions peak omphacite. age eclogite metamorphism has constrained U-Pb SHRIMP dating zircon 2093 ± 45 Ma. are associated with 2.05 Ga old charnockites mafic granulites containing textures characteristic for near-isobaric cooling. These rocks represent plate above subduction which were tectonically emplaced. With an 2.09 Complex older than other related Ubendian (1.88 Ga) Usagaran belts (2.0 southern border Tanzania Craton. They also Belomorian province (1.9 Ga; Russia) thus oldest known outcropping orogenic belt. African (all MORB chemistry) indicate during formation Nuna supercontinent lithosphere around Congo-Tanzania Craton was thick, cold rigid enough become subducted modern tectonic regime. However, apparent geothermal gradients 12–14 °C/km higher Neoproterozoic Phanerozoic interpreted result warm hotter Earth.