Continental Material in the Oceans

In recent years there have been diverse reports of material in the lithosphere under the oceans, away from continental shelves, that does not comprise classical oceanic crust underlain by progressively mantle lithosphere that thickens according to plate-cooling models. These reports come from multiple different research approaches including:

• Marine geophysical surveying and sampling, identifying microcontinents, e.g., the Jan Mayen Microcontinent Complex, and ”orogenic bridges”, e.g., the Davis Strait;
• Deep seismic profiling detecting continental material beneath surface basalts, e.g., the Alpha-Mendeleev Rise;
• Large-scale seismic imaging using teleseismic earthquakes, identifying lithosphere with continental characteristics, e.g., in the South Atlantic;
• Aeromagnetic surveying revealing the extent of seafloor-spreading-related anomalies, e.g., in the Fram Strait;
• Broad cross-disciplinary work identifying crust inconsistent with a purely basaltic composition, e.g. the Greenland-Iceland-Faroe Ridge;
• Direct observation, e.g., on the Rio Grande Rise;
• Geochemistry, e.g., on the South West Indian Ridge;
• Dating of zircons from igneous rocks in the oceans that pre-date the time of formation of the local oceanic crust, e.g., Mauritius.

Understanding the extent of continental material in the oceans, and acceptance that hybrid continental/oceanic crust may exist – a third kind of crust – is an emerging field. At present no systematic review has been done of potential continental or hybrid regions in the oceans away from continental margins. It is thus unknown how widespread it might be and there is no broad understanding of or how it got there and why. It is timely for a systematic review of the subject aimed at identifying key research targets for the future.