Geophysical characterisation of the ocean–continent transition at magma-poor rifted margins

Geophysical characterisation of the ocean–continent transition (OCT) at magma-poor rifted margins has focused primarily on the determination of P wave velocities using wide-angle seismic techniques. Such experiments have shown that the OCT is heterogeneous, but that typically velocities increase gradually with depth from ∼ 5.0 km/s at top basement to ∼ 8.0 km/s at ∼ 5 km deeper, without a large and abrupt Moho transition. The velocity variation with depth is similar to that of old fracture zone crust, and appears to differ from that of oceanic crust formed at ultraslow spreading rates, though sampling of the latter is limited. Typically, the OCT is characterised by weakly lineated, low amplitude magnetic anomalies; the interpretation of these anomalies remains controversial. The oceanward limit of the OCT remains poorly defined on many margins.