Researchers Map Layers of Lava Flows Beneath North Atlantic; New Technique to Further Oil Exploration
|Location of seismic profiles across the North Atlantic. Click to enlarge.|
Scientists have mapped the layers of once molten rock that lie beneath the North Atlantic Ocean and which measure more than eight miles thick in some locations. The research, reported in the journal Nature, provides a better understanding of what may have happened during the break-up of continents to form new mid-ocean ridges. The same volcanic activity in the North Atlantic may also have caused the subsequent release of massive volumes of greenhouse gases which led to a spike in global temperatures 55 million years ago.
The scientists, led by Professor Robert White, FRS at the University of Cambridge (UK), also developed a new method of seeing through the thick lava flows beneath the seafloor to the sediments and structures beneath. The technique is now being employed to further oil exploration of the area which was previously restricted by the inability to image through the lava flows.
The research was funded by a university-industry research group, which included Cambridge and Liverpool Universities, Schlumberger Cambridge Research Ltd and Badley Geoscience Ltd, with major funding input from WesternGeco, the Natural Environment Research Council, the Department of Trade and Industry, and eight oil companies.
When a continent breaks apart, as Greenland and Northwest Europe did 55 million years ago, it is sometimes accompanied by a massive outburst of volcanic activity due to a hot spot in the mantle that lies beneath the crust of the earth. When the North Atlantic broke open, it produced 1–2 million cubic miles (5–10 million cubic kilometers) of molten rock which extended across 300,000 square miles (one million square kilometers). Most of the volcanic rock is now underwater and buried by more recent sediments. However, the edge of this huge volcanic region is visible on land in a few places including the Giant’s Causeway in Northern Ireland.
For the first time scientists mapped the huge quantities of molten rock in the North Atlantic. The rock had been injected into the crust of the earth at a depth of 5–10 miles (10–20 kilometers) beneath the surface along the line of the continental breakup 55 million years ago. Using seismic methods, they were able to map the layers of lava flows both near the surface and deep into the earth.
There is a considerable controversy at present as to whether the large scale volcanism was caused by abnormally hot mantle deep in the earth (a hot spot) or whether it was caused by some other means, such as a compositional change in the mantle that mean it could more easily be melted. The researchers demonstrate in this paper that the volcanic activity requires a temperature anomaly, supporting the hot spot model.
Additionally, the scientists hope that a better understanding of what happened 55 million years ago will also provide insight into the changes that occur to the atmosphere and biosphere during volcanic activity.
At the time of the break-up of the North Atlantic 55 million years ago there was a very sudden increase in global temperatures: in fact the earth has never been as hot since then, although the global warming that humans are now causing is likely to take the earth back to the same high temperatures as existed for a short period then.
The increases in global temperatures are thought to have been caused by a massive release of methane from under the seabed – methane is almost 25 times worse than carbon dioxide as a greenhouse gas. A better understanding of volcanism and the underlying hot spot will help us understand how such activity might have triggered the methane release and subsequent global warming.—Professor Robert White
The researchers’ findings also have implications for oil exploration in the region. Large volumes of oil have already been discovered (and are being extracted) in the sediments under the seabed between the Shetland Islands and the Faroe Islands. If these same sediments extend westward towards the Faroe Islands, as geological models suggest they do, there may be more oil to be found.
Conventional exploration techniques have not been able to penetrate the thick layers of lava flows that poured over them at the time the North Atlantic broke open. Techniques developed in conjunction with the mapping research enable the penetration of the molten rock layer to the sediments and structures that lie beneath them.
R. S. White, et. al.; Lower-crustal intrusion on the North Atlantic continental margin; Nature 452, 460-464 (27 March 2008) | DOI: 10.1038/nature06687