Palaeomagnetic results from the late Precambrian Chela Group of southwest Angola

Abstract

Palaeomagnetic results from fourteen sites (56 samples) in the late Precambrian Chela Group of southwest Angola are reported. After alternating field demagnetization eight of the sites have mean directions closely grouped around D = 123°, I = −44 1 2 ° ; the dispersion of these directions increases substantially after tectonic corrections suggesting magnetic overprinting. Intensive thermal demagnetization proved more effective than alternating field demagnetization in resolving magnetic components. After removal of viscous components, samples from five sites (Group I) show a single component, similar to that observed after alternating field demagnetization. At four more sites (Group II) this same component is present together with another higher-temperature component. The mean direction for the component observed at all nine sites is D = 119.7°, I = −45.9° with k = 40.5. Tectonic corrections produced little change in mean direction but reduced k to 4.5; the data supports the magnetic overprint hypothesis. A high blocking temperature component was resolved by remagnetization circle analysis of three flat-lying sites (Group III) and this component is similar to the higher-temperature component observed at site DG (Group II) after tectonic correction has been made. The component observed in Group III samples ( D = 311°, I = 49°), confirmed by some samples from Group II, is similar to that observed in the Nosib Group just to the south in Namibia. It is suggested that the mean Group III result gives the primary direction of the Chela Group, that the data support the correlation of the Nosib and Chela Groups and that the Chela rocks were overprinted magnetically during an event subsequent to their tilting.