Aeromagnetic tests for continental drift in Africa and South America

Abstract

Aeromagnetic data from parts of the east coast of South America and the west coast of Africa have been compiled and compared. The data available include detailed surveys in Africa over Sierra Leone, the Ivory Coast and Ghana and in South America over Guyana and Surinam. These show a distinct character difference along a boundary between the east and west of the middle of the Ivory Coast. The western pattern is a pronounced, banded pattern of highs and lows trending approximately N 20–40°E, with wavelengths of about 30 km and total amplitudes of 500–800 gammas. To the east, the pattern is quite different as no banding is present and only more local features can be detected. In South America a series of anomalies strike N 45°E, with wavelengths and amplitudes similar to those found in the Ivory Coast. New data from high altitude aeromagnetic surveys have been flown over Africa and South America. These confirm the patterns found in the detailed surveys and show that the Brazilian shield area is quite different magnetically than the Guiana shield. Instead it resembles the eastern part of the African area under study. It therefore appears that the shield in the Ivory Coast in Africa and in the vicinity of the Amazon trough in South America can be divided into two portions. When the two continents are refitted these lines become one continuous ancient geologic “tie line” between the continents. This sort of tie line based on magnetic anomaly character provides yet another constraint in precise pre-drift continental reconstructions.