Mesozoic magnetic anomalies in the southern Natal Valley

Abstract

The recognition of Mesozoic magnetic anomalies M0-M12 within the submarine Natal Valley (south-west Indian Ocean) provides a further constraint on the relative motion between South America (Falkland Plateau) and Africa during the early opening phase of West Gondwanaland (Fig. 1). Colinear with M12, magnetic anomaly G (ref. 1) is delineated north of the South Tugela Ridge², an acoustic basement high which is suspected to have been emplaced within continental crust immediately north of the continental–oceanic crust boundary (COB) during the initial rifting phase. Starting from a revised West Gondwana reconstruction³ and using palaeo-poles of rotation^1,3, the Falkland Plateau can be rotated into the Natal Valley superposing the corresponding Georgia Basin and Natal Valley magnetic anomalies. This achieves an optimum continuity of inter-continental structural lineaments³ by overlapping of an anomaly intermediate to M10 and M11 (∑M10N⁴). This suggests that the Natal Valley COB is located between anomalies M10 and M11, implying that in this zone of south-west Gondwana, seafloor spreading commenced at ∼125 Myr.